diff --git a/package.json b/package.json
index ac75816f8..5e2acc4f0 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "js-slang",
-  "version": "1.0.62",
+  "version": "1.0.63",
   "license": "Apache-2.0",
   "description": "Javascript-based implementations of Source, written in Typescript",
   "keywords": [
diff --git a/src/cse-machine/__tests__/__snapshots__/cse-machine-heap.ts.snap b/src/cse-machine/__tests__/__snapshots__/cse-machine-heap.ts.snap
index ae1901f12..d571e7912 100644
--- a/src/cse-machine/__tests__/__snapshots__/cse-machine-heap.ts.snap
+++ b/src/cse-machine/__tests__/__snapshots__/cse-machine-heap.ts.snap
@@ -1,6 +1,6 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`Arrays and closures are correctly added to their respective environment heaps 1`] = `
+exports[`Arrays and closures are correctly added to their respective heaps 1`] = `
 EnvTree {
   "_root": EnvTreeNode {
     "_children": Array [
@@ -3183,7 +3183,7 @@ EnvTree {
 }
 `;
 
-exports[`Arrays created from in-built functions are correctly added to the environment heap 1`] = `
+exports[`Arrays created from built-in functions are correctly added to their respective heaps 1`] = `
 EnvTree {
   "_root": EnvTreeNode {
     "_children": Array [
@@ -4427,7 +4427,7 @@ EnvTree {
 }
 `;
 
-exports[`Pre-defined functions are correctly added to prelude environment heap 1`] = `
+exports[`Pre-defined functions are correctly added to prelude heap 1`] = `
 EnvTree {
   "_root": EnvTreeNode {
     "_children": Array [
@@ -5570,3 +5570,6363 @@ EnvTree {
   },
 }
 `;
+
+exports[`Variadic closures correctly add argument array to the function environment heap 1`] = `
+EnvTree {
+  "_root": EnvTreeNode {
+    "_children": Array [
+      EnvTreeNode {
+        "_children": Array [
+          EnvTreeNode {
+            "_children": Array [],
+            "environment": Object {
+              "callExpression": Object {
+                "arguments": Array [
+                  Object {
+                    "loc": undefined,
+                    "type": "Literal",
+                    "value": 1,
+                  },
+                  Object {
+                    "loc": undefined,
+                    "type": "Literal",
+                    "value": 2,
+                  },
+                  Object {
+                    "loc": undefined,
+                    "type": "Literal",
+                    "value": 3,
+                  },
+                ],
+                "callee": Node {
+                  "end": 24,
+                  "loc": SourceLocation {
+                    "end": Position {
+                      "column": 1,
+                      "line": 2,
+                    },
+                    "start": Position {
+                      "column": 0,
+                      "line": 2,
+                    },
+                  },
+                  "name": "f",
+                  "start": 23,
+                  "type": "Identifier",
+                },
+                "end": 33,
+                "loc": SourceLocation {
+                  "end": Position {
+                    "column": 10,
+                    "line": 2,
+                  },
+                  "start": Position {
+                    "column": 0,
+                    "line": 2,
+                  },
+                },
+                "start": 23,
+                "type": "CallExpression",
+              },
+              "head": Object {
+                "x": Array [
+                  1,
+                  2,
+                  3,
+                ],
+              },
+              "heap": Heap {
+                "storage": Set {
+                  Array [
+                    1,
+                    2,
+                    3,
+                  ],
+                },
+              },
+              "id": "2",
+              "name": "f",
+              "tail": Object {
+                "head": Object {
+                  "f": [Function],
+                },
+                "heap": Heap {
+                  "storage": Set {
+                    [Function],
+                  },
+                },
+                "id": "0",
+                "name": "programEnvironment",
+                "tail": Object {
+                  "head": Object {
+                    "Infinity": Infinity,
+                    "NaN": NaN,
+                    "apply_in_underlying_javascript": [Function],
+                    "arity": [Function],
+                    "array_length": [Function],
+                    "call_cc": [Function],
+                    "char_at": [Function],
+                    "display": [Function],
+                    "display_list": [Function],
+                    "draw_data": [Function],
+                    "error": [Function],
+                    "get_time": [Function],
+                    "head": [Function],
+                    "is_array": [Function],
+                    "is_boolean": [Function],
+                    "is_function": [Function],
+                    "is_list": [Function],
+                    "is_null": [Function],
+                    "is_number": [Function],
+                    "is_pair": [Function],
+                    "is_string": [Function],
+                    "is_undefined": [Function],
+                    "list": [Function],
+                    "math_E": 2.718281828459045,
+                    "math_LN10": 2.302585092994046,
+                    "math_LN2": 0.6931471805599453,
+                    "math_LOG10E": 0.4342944819032518,
+                    "math_LOG2E": 1.4426950408889634,
+                    "math_PI": 3.141592653589793,
+                    "math_SQRT1_2": 0.7071067811865476,
+                    "math_SQRT2": 1.4142135623730951,
+                    "math_abs": [Function],
+                    "math_acos": [Function],
+                    "math_acosh": [Function],
+                    "math_asin": [Function],
+                    "math_asinh": [Function],
+                    "math_atan": [Function],
+                    "math_atan2": [Function],
+                    "math_atanh": [Function],
+                    "math_cbrt": [Function],
+                    "math_ceil": [Function],
+                    "math_clz32": [Function],
+                    "math_cos": [Function],
+                    "math_cosh": [Function],
+                    "math_exp": [Function],
+                    "math_expm1": [Function],
+                    "math_floor": [Function],
+                    "math_fround": [Function],
+                    "math_hypot": [Function],
+                    "math_imul": [Function],
+                    "math_log": [Function],
+                    "math_log10": [Function],
+                    "math_log1p": [Function],
+                    "math_log2": [Function],
+                    "math_max": [Function],
+                    "math_min": [Function],
+                    "math_pow": [Function],
+                    "math_random": [Function],
+                    "math_round": [Function],
+                    "math_sign": [Function],
+                    "math_sin": [Function],
+                    "math_sinh": [Function],
+                    "math_sqrt": [Function],
+                    "math_tan": [Function],
+                    "math_tanh": [Function],
+                    "math_trunc": [Function],
+                    "pair": [Function],
+                    "parse": [Function],
+                    "parse_int": [Function],
+                    "prompt": [Function],
+                    "raw_display": [Function],
+                    "set_head": [Function],
+                    "set_tail": [Function],
+                    "stream": [Function],
+                    "stringify": [Function],
+                    "tail": [Function],
+                    "tokenize": [Function],
+                    "undefined": undefined,
+                  },
+                  "heap": Heap {
+                    "storage": null,
+                  },
+                  "id": "-1",
+                  "name": "global",
+                  "tail": null,
+                },
+              },
+            },
+            "parent": [Circular],
+          },
+        ],
+        "environment": Object {
+          "head": Object {
+            "f": [Function],
+          },
+          "heap": Heap {
+            "storage": Set {
+              [Function],
+            },
+          },
+          "id": "0",
+          "name": "programEnvironment",
+          "tail": Object {
+            "head": Object {
+              "Infinity": Infinity,
+              "NaN": NaN,
+              "apply_in_underlying_javascript": [Function],
+              "arity": [Function],
+              "array_length": [Function],
+              "call_cc": [Function],
+              "char_at": [Function],
+              "display": [Function],
+              "display_list": [Function],
+              "draw_data": [Function],
+              "error": [Function],
+              "get_time": [Function],
+              "head": [Function],
+              "is_array": [Function],
+              "is_boolean": [Function],
+              "is_function": [Function],
+              "is_list": [Function],
+              "is_null": [Function],
+              "is_number": [Function],
+              "is_pair": [Function],
+              "is_string": [Function],
+              "is_undefined": [Function],
+              "list": [Function],
+              "math_E": 2.718281828459045,
+              "math_LN10": 2.302585092994046,
+              "math_LN2": 0.6931471805599453,
+              "math_LOG10E": 0.4342944819032518,
+              "math_LOG2E": 1.4426950408889634,
+              "math_PI": 3.141592653589793,
+              "math_SQRT1_2": 0.7071067811865476,
+              "math_SQRT2": 1.4142135623730951,
+              "math_abs": [Function],
+              "math_acos": [Function],
+              "math_acosh": [Function],
+              "math_asin": [Function],
+              "math_asinh": [Function],
+              "math_atan": [Function],
+              "math_atan2": [Function],
+              "math_atanh": [Function],
+              "math_cbrt": [Function],
+              "math_ceil": [Function],
+              "math_clz32": [Function],
+              "math_cos": [Function],
+              "math_cosh": [Function],
+              "math_exp": [Function],
+              "math_expm1": [Function],
+              "math_floor": [Function],
+              "math_fround": [Function],
+              "math_hypot": [Function],
+              "math_imul": [Function],
+              "math_log": [Function],
+              "math_log10": [Function],
+              "math_log1p": [Function],
+              "math_log2": [Function],
+              "math_max": [Function],
+              "math_min": [Function],
+              "math_pow": [Function],
+              "math_random": [Function],
+              "math_round": [Function],
+              "math_sign": [Function],
+              "math_sin": [Function],
+              "math_sinh": [Function],
+              "math_sqrt": [Function],
+              "math_tan": [Function],
+              "math_tanh": [Function],
+              "math_trunc": [Function],
+              "pair": [Function],
+              "parse": [Function],
+              "parse_int": [Function],
+              "prompt": [Function],
+              "raw_display": [Function],
+              "set_head": [Function],
+              "set_tail": [Function],
+              "stream": [Function],
+              "stringify": [Function],
+              "tail": [Function],
+              "tokenize": [Function],
+              "undefined": undefined,
+            },
+            "heap": Heap {
+              "storage": null,
+            },
+            "id": "-1",
+            "name": "global",
+            "tail": null,
+          },
+        },
+        "parent": [Circular],
+      },
+    ],
+    "environment": Object {
+      "head": Object {
+        "Infinity": Infinity,
+        "NaN": NaN,
+        "apply_in_underlying_javascript": [Function],
+        "arity": [Function],
+        "array_length": [Function],
+        "call_cc": [Function],
+        "char_at": [Function],
+        "display": [Function],
+        "display_list": [Function],
+        "draw_data": [Function],
+        "error": [Function],
+        "get_time": [Function],
+        "head": [Function],
+        "is_array": [Function],
+        "is_boolean": [Function],
+        "is_function": [Function],
+        "is_list": [Function],
+        "is_null": [Function],
+        "is_number": [Function],
+        "is_pair": [Function],
+        "is_string": [Function],
+        "is_undefined": [Function],
+        "list": [Function],
+        "math_E": 2.718281828459045,
+        "math_LN10": 2.302585092994046,
+        "math_LN2": 0.6931471805599453,
+        "math_LOG10E": 0.4342944819032518,
+        "math_LOG2E": 1.4426950408889634,
+        "math_PI": 3.141592653589793,
+        "math_SQRT1_2": 0.7071067811865476,
+        "math_SQRT2": 1.4142135623730951,
+        "math_abs": [Function],
+        "math_acos": [Function],
+        "math_acosh": [Function],
+        "math_asin": [Function],
+        "math_asinh": [Function],
+        "math_atan": [Function],
+        "math_atan2": [Function],
+        "math_atanh": [Function],
+        "math_cbrt": [Function],
+        "math_ceil": [Function],
+        "math_clz32": [Function],
+        "math_cos": [Function],
+        "math_cosh": [Function],
+        "math_exp": [Function],
+        "math_expm1": [Function],
+        "math_floor": [Function],
+        "math_fround": [Function],
+        "math_hypot": [Function],
+        "math_imul": [Function],
+        "math_log": [Function],
+        "math_log10": [Function],
+        "math_log1p": [Function],
+        "math_log2": [Function],
+        "math_max": [Function],
+        "math_min": [Function],
+        "math_pow": [Function],
+        "math_random": [Function],
+        "math_round": [Function],
+        "math_sign": [Function],
+        "math_sin": [Function],
+        "math_sinh": [Function],
+        "math_sqrt": [Function],
+        "math_tan": [Function],
+        "math_tanh": [Function],
+        "math_trunc": [Function],
+        "pair": [Function],
+        "parse": [Function],
+        "parse_int": [Function],
+        "prompt": [Function],
+        "raw_display": [Function],
+        "set_head": [Function],
+        "set_tail": [Function],
+        "stream": [Function],
+        "stringify": [Function],
+        "tail": [Function],
+        "tokenize": [Function],
+        "undefined": undefined,
+      },
+      "heap": Heap {
+        "storage": null,
+      },
+      "id": "-1",
+      "name": "global",
+      "tail": null,
+    },
+    "parent": null,
+  },
+  "map": Map {
+    Object {
+      "head": Object {
+        "Infinity": Infinity,
+        "NaN": NaN,
+        "apply_in_underlying_javascript": [Function],
+        "arity": [Function],
+        "array_length": [Function],
+        "call_cc": [Function],
+        "char_at": [Function],
+        "display": [Function],
+        "display_list": [Function],
+        "draw_data": [Function],
+        "error": [Function],
+        "get_time": [Function],
+        "head": [Function],
+        "is_array": [Function],
+        "is_boolean": [Function],
+        "is_function": [Function],
+        "is_list": [Function],
+        "is_null": [Function],
+        "is_number": [Function],
+        "is_pair": [Function],
+        "is_string": [Function],
+        "is_undefined": [Function],
+        "list": [Function],
+        "math_E": 2.718281828459045,
+        "math_LN10": 2.302585092994046,
+        "math_LN2": 0.6931471805599453,
+        "math_LOG10E": 0.4342944819032518,
+        "math_LOG2E": 1.4426950408889634,
+        "math_PI": 3.141592653589793,
+        "math_SQRT1_2": 0.7071067811865476,
+        "math_SQRT2": 1.4142135623730951,
+        "math_abs": [Function],
+        "math_acos": [Function],
+        "math_acosh": [Function],
+        "math_asin": [Function],
+        "math_asinh": [Function],
+        "math_atan": [Function],
+        "math_atan2": [Function],
+        "math_atanh": [Function],
+        "math_cbrt": [Function],
+        "math_ceil": [Function],
+        "math_clz32": [Function],
+        "math_cos": [Function],
+        "math_cosh": [Function],
+        "math_exp": [Function],
+        "math_expm1": [Function],
+        "math_floor": [Function],
+        "math_fround": [Function],
+        "math_hypot": [Function],
+        "math_imul": [Function],
+        "math_log": [Function],
+        "math_log10": [Function],
+        "math_log1p": [Function],
+        "math_log2": [Function],
+        "math_max": [Function],
+        "math_min": [Function],
+        "math_pow": [Function],
+        "math_random": [Function],
+        "math_round": [Function],
+        "math_sign": [Function],
+        "math_sin": [Function],
+        "math_sinh": [Function],
+        "math_sqrt": [Function],
+        "math_tan": [Function],
+        "math_tanh": [Function],
+        "math_trunc": [Function],
+        "pair": [Function],
+        "parse": [Function],
+        "parse_int": [Function],
+        "prompt": [Function],
+        "raw_display": [Function],
+        "set_head": [Function],
+        "set_tail": [Function],
+        "stream": [Function],
+        "stringify": [Function],
+        "tail": [Function],
+        "tokenize": [Function],
+        "undefined": undefined,
+      },
+      "heap": Heap {
+        "storage": null,
+      },
+      "id": "-1",
+      "name": "global",
+      "tail": null,
+    } => EnvTreeNode {
+      "_children": Array [
+        EnvTreeNode {
+          "_children": Array [
+            EnvTreeNode {
+              "_children": Array [],
+              "environment": Object {
+                "callExpression": Object {
+                  "arguments": Array [
+                    Object {
+                      "loc": undefined,
+                      "type": "Literal",
+                      "value": 1,
+                    },
+                    Object {
+                      "loc": undefined,
+                      "type": "Literal",
+                      "value": 2,
+                    },
+                    Object {
+                      "loc": undefined,
+                      "type": "Literal",
+                      "value": 3,
+                    },
+                  ],
+                  "callee": Node {
+                    "end": 24,
+                    "loc": SourceLocation {
+                      "end": Position {
+                        "column": 1,
+                        "line": 2,
+                      },
+                      "start": Position {
+                        "column": 0,
+                        "line": 2,
+                      },
+                    },
+                    "name": "f",
+                    "start": 23,
+                    "type": "Identifier",
+                  },
+                  "end": 33,
+                  "loc": SourceLocation {
+                    "end": Position {
+                      "column": 10,
+                      "line": 2,
+                    },
+                    "start": Position {
+                      "column": 0,
+                      "line": 2,
+                    },
+                  },
+                  "start": 23,
+                  "type": "CallExpression",
+                },
+                "head": Object {
+                  "x": Array [
+                    1,
+                    2,
+                    3,
+                  ],
+                },
+                "heap": Heap {
+                  "storage": Set {
+                    Array [
+                      1,
+                      2,
+                      3,
+                    ],
+                  },
+                },
+                "id": "2",
+                "name": "f",
+                "tail": Object {
+                  "head": Object {
+                    "f": [Function],
+                  },
+                  "heap": Heap {
+                    "storage": Set {
+                      [Function],
+                    },
+                  },
+                  "id": "0",
+                  "name": "programEnvironment",
+                  "tail": Object {
+                    "head": Object {
+                      "Infinity": Infinity,
+                      "NaN": NaN,
+                      "apply_in_underlying_javascript": [Function],
+                      "arity": [Function],
+                      "array_length": [Function],
+                      "call_cc": [Function],
+                      "char_at": [Function],
+                      "display": [Function],
+                      "display_list": [Function],
+                      "draw_data": [Function],
+                      "error": [Function],
+                      "get_time": [Function],
+                      "head": [Function],
+                      "is_array": [Function],
+                      "is_boolean": [Function],
+                      "is_function": [Function],
+                      "is_list": [Function],
+                      "is_null": [Function],
+                      "is_number": [Function],
+                      "is_pair": [Function],
+                      "is_string": [Function],
+                      "is_undefined": [Function],
+                      "list": [Function],
+                      "math_E": 2.718281828459045,
+                      "math_LN10": 2.302585092994046,
+                      "math_LN2": 0.6931471805599453,
+                      "math_LOG10E": 0.4342944819032518,
+                      "math_LOG2E": 1.4426950408889634,
+                      "math_PI": 3.141592653589793,
+                      "math_SQRT1_2": 0.7071067811865476,
+                      "math_SQRT2": 1.4142135623730951,
+                      "math_abs": [Function],
+                      "math_acos": [Function],
+                      "math_acosh": [Function],
+                      "math_asin": [Function],
+                      "math_asinh": [Function],
+                      "math_atan": [Function],
+                      "math_atan2": [Function],
+                      "math_atanh": [Function],
+                      "math_cbrt": [Function],
+                      "math_ceil": [Function],
+                      "math_clz32": [Function],
+                      "math_cos": [Function],
+                      "math_cosh": [Function],
+                      "math_exp": [Function],
+                      "math_expm1": [Function],
+                      "math_floor": [Function],
+                      "math_fround": [Function],
+                      "math_hypot": [Function],
+                      "math_imul": [Function],
+                      "math_log": [Function],
+                      "math_log10": [Function],
+                      "math_log1p": [Function],
+                      "math_log2": [Function],
+                      "math_max": [Function],
+                      "math_min": [Function],
+                      "math_pow": [Function],
+                      "math_random": [Function],
+                      "math_round": [Function],
+                      "math_sign": [Function],
+                      "math_sin": [Function],
+                      "math_sinh": [Function],
+                      "math_sqrt": [Function],
+                      "math_tan": [Function],
+                      "math_tanh": [Function],
+                      "math_trunc": [Function],
+                      "pair": [Function],
+                      "parse": [Function],
+                      "parse_int": [Function],
+                      "prompt": [Function],
+                      "raw_display": [Function],
+                      "set_head": [Function],
+                      "set_tail": [Function],
+                      "stream": [Function],
+                      "stringify": [Function],
+                      "tail": [Function],
+                      "tokenize": [Function],
+                      "undefined": undefined,
+                    },
+                    "heap": Heap {
+                      "storage": null,
+                    },
+                    "id": "-1",
+                    "name": "global",
+                    "tail": null,
+                  },
+                },
+              },
+              "parent": [Circular],
+            },
+          ],
+          "environment": Object {
+            "head": Object {
+              "f": [Function],
+            },
+            "heap": Heap {
+              "storage": Set {
+                [Function],
+              },
+            },
+            "id": "0",
+            "name": "programEnvironment",
+            "tail": Object {
+              "head": Object {
+                "Infinity": Infinity,
+                "NaN": NaN,
+                "apply_in_underlying_javascript": [Function],
+                "arity": [Function],
+                "array_length": [Function],
+                "call_cc": [Function],
+                "char_at": [Function],
+                "display": [Function],
+                "display_list": [Function],
+                "draw_data": [Function],
+                "error": [Function],
+                "get_time": [Function],
+                "head": [Function],
+                "is_array": [Function],
+                "is_boolean": [Function],
+                "is_function": [Function],
+                "is_list": [Function],
+                "is_null": [Function],
+                "is_number": [Function],
+                "is_pair": [Function],
+                "is_string": [Function],
+                "is_undefined": [Function],
+                "list": [Function],
+                "math_E": 2.718281828459045,
+                "math_LN10": 2.302585092994046,
+                "math_LN2": 0.6931471805599453,
+                "math_LOG10E": 0.4342944819032518,
+                "math_LOG2E": 1.4426950408889634,
+                "math_PI": 3.141592653589793,
+                "math_SQRT1_2": 0.7071067811865476,
+                "math_SQRT2": 1.4142135623730951,
+                "math_abs": [Function],
+                "math_acos": [Function],
+                "math_acosh": [Function],
+                "math_asin": [Function],
+                "math_asinh": [Function],
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+            "math_imul": [Function],
+            "math_log": [Function],
+            "math_log10": [Function],
+            "math_log1p": [Function],
+            "math_log2": [Function],
+            "math_max": [Function],
+            "math_min": [Function],
+            "math_pow": [Function],
+            "math_random": [Function],
+            "math_round": [Function],
+            "math_sign": [Function],
+            "math_sin": [Function],
+            "math_sinh": [Function],
+            "math_sqrt": [Function],
+            "math_tan": [Function],
+            "math_tanh": [Function],
+            "math_trunc": [Function],
+            "pair": [Function],
+            "parse": [Function],
+            "parse_int": [Function],
+            "prompt": [Function],
+            "raw_display": [Function],
+            "set_head": [Function],
+            "set_tail": [Function],
+            "stream": [Function],
+            "stringify": [Function],
+            "tail": [Function],
+            "tokenize": [Function],
+            "undefined": undefined,
+          },
+          "heap": Heap {
+            "storage": null,
+          },
+          "id": "-1",
+          "name": "global",
+          "tail": null,
+        },
+      },
+    } => EnvTreeNode {
+      "_children": Array [],
+      "environment": Object {
+        "callExpression": Object {
+          "arguments": Array [
+            Object {
+              "loc": undefined,
+              "type": "Literal",
+              "value": 1,
+            },
+            Object {
+              "loc": undefined,
+              "type": "Literal",
+              "value": 2,
+            },
+            Object {
+              "loc": undefined,
+              "type": "Literal",
+              "value": 3,
+            },
+          ],
+          "callee": Node {
+            "end": 24,
+            "loc": SourceLocation {
+              "end": Position {
+                "column": 1,
+                "line": 2,
+              },
+              "start": Position {
+                "column": 0,
+                "line": 2,
+              },
+            },
+            "name": "f",
+            "start": 23,
+            "type": "Identifier",
+          },
+          "end": 33,
+          "loc": SourceLocation {
+            "end": Position {
+              "column": 10,
+              "line": 2,
+            },
+            "start": Position {
+              "column": 0,
+              "line": 2,
+            },
+          },
+          "start": 23,
+          "type": "CallExpression",
+        },
+        "head": Object {
+          "x": Array [
+            1,
+            2,
+            3,
+          ],
+        },
+        "heap": Heap {
+          "storage": Set {
+            Array [
+              1,
+              2,
+              3,
+            ],
+          },
+        },
+        "id": "2",
+        "name": "f",
+        "tail": Object {
+          "head": Object {
+            "f": [Function],
+          },
+          "heap": Heap {
+            "storage": Set {
+              [Function],
+            },
+          },
+          "id": "0",
+          "name": "programEnvironment",
+          "tail": Object {
+            "head": Object {
+              "Infinity": Infinity,
+              "NaN": NaN,
+              "apply_in_underlying_javascript": [Function],
+              "arity": [Function],
+              "array_length": [Function],
+              "call_cc": [Function],
+              "char_at": [Function],
+              "display": [Function],
+              "display_list": [Function],
+              "draw_data": [Function],
+              "error": [Function],
+              "get_time": [Function],
+              "head": [Function],
+              "is_array": [Function],
+              "is_boolean": [Function],
+              "is_function": [Function],
+              "is_list": [Function],
+              "is_null": [Function],
+              "is_number": [Function],
+              "is_pair": [Function],
+              "is_string": [Function],
+              "is_undefined": [Function],
+              "list": [Function],
+              "math_E": 2.718281828459045,
+              "math_LN10": 2.302585092994046,
+              "math_LN2": 0.6931471805599453,
+              "math_LOG10E": 0.4342944819032518,
+              "math_LOG2E": 1.4426950408889634,
+              "math_PI": 3.141592653589793,
+              "math_SQRT1_2": 0.7071067811865476,
+              "math_SQRT2": 1.4142135623730951,
+              "math_abs": [Function],
+              "math_acos": [Function],
+              "math_acosh": [Function],
+              "math_asin": [Function],
+              "math_asinh": [Function],
+              "math_atan": [Function],
+              "math_atan2": [Function],
+              "math_atanh": [Function],
+              "math_cbrt": [Function],
+              "math_ceil": [Function],
+              "math_clz32": [Function],
+              "math_cos": [Function],
+              "math_cosh": [Function],
+              "math_exp": [Function],
+              "math_expm1": [Function],
+              "math_floor": [Function],
+              "math_fround": [Function],
+              "math_hypot": [Function],
+              "math_imul": [Function],
+              "math_log": [Function],
+              "math_log10": [Function],
+              "math_log1p": [Function],
+              "math_log2": [Function],
+              "math_max": [Function],
+              "math_min": [Function],
+              "math_pow": [Function],
+              "math_random": [Function],
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+              "math_sign": [Function],
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+              "math_sqrt": [Function],
+              "math_tan": [Function],
+              "math_tanh": [Function],
+              "math_trunc": [Function],
+              "pair": [Function],
+              "parse": [Function],
+              "parse_int": [Function],
+              "prompt": [Function],
+              "raw_display": [Function],
+              "set_head": [Function],
+              "set_tail": [Function],
+              "stream": [Function],
+              "stringify": [Function],
+              "tail": [Function],
+              "tokenize": [Function],
+              "undefined": undefined,
+            },
+            "heap": Heap {
+              "storage": null,
+            },
+            "id": "-1",
+            "name": "global",
+            "tail": null,
+          },
+        },
+      },
+      "parent": EnvTreeNode {
+        "_children": Array [
+          [Circular],
+        ],
+        "environment": Object {
+          "head": Object {
+            "f": [Function],
+          },
+          "heap": Heap {
+            "storage": Set {
+              [Function],
+            },
+          },
+          "id": "0",
+          "name": "programEnvironment",
+          "tail": Object {
+            "head": Object {
+              "Infinity": Infinity,
+              "NaN": NaN,
+              "apply_in_underlying_javascript": [Function],
+              "arity": [Function],
+              "array_length": [Function],
+              "call_cc": [Function],
+              "char_at": [Function],
+              "display": [Function],
+              "display_list": [Function],
+              "draw_data": [Function],
+              "error": [Function],
+              "get_time": [Function],
+              "head": [Function],
+              "is_array": [Function],
+              "is_boolean": [Function],
+              "is_function": [Function],
+              "is_list": [Function],
+              "is_null": [Function],
+              "is_number": [Function],
+              "is_pair": [Function],
+              "is_string": [Function],
+              "is_undefined": [Function],
+              "list": [Function],
+              "math_E": 2.718281828459045,
+              "math_LN10": 2.302585092994046,
+              "math_LN2": 0.6931471805599453,
+              "math_LOG10E": 0.4342944819032518,
+              "math_LOG2E": 1.4426950408889634,
+              "math_PI": 3.141592653589793,
+              "math_SQRT1_2": 0.7071067811865476,
+              "math_SQRT2": 1.4142135623730951,
+              "math_abs": [Function],
+              "math_acos": [Function],
+              "math_acosh": [Function],
+              "math_asin": [Function],
+              "math_asinh": [Function],
+              "math_atan": [Function],
+              "math_atan2": [Function],
+              "math_atanh": [Function],
+              "math_cbrt": [Function],
+              "math_ceil": [Function],
+              "math_clz32": [Function],
+              "math_cos": [Function],
+              "math_cosh": [Function],
+              "math_exp": [Function],
+              "math_expm1": [Function],
+              "math_floor": [Function],
+              "math_fround": [Function],
+              "math_hypot": [Function],
+              "math_imul": [Function],
+              "math_log": [Function],
+              "math_log10": [Function],
+              "math_log1p": [Function],
+              "math_log2": [Function],
+              "math_max": [Function],
+              "math_min": [Function],
+              "math_pow": [Function],
+              "math_random": [Function],
+              "math_round": [Function],
+              "math_sign": [Function],
+              "math_sin": [Function],
+              "math_sinh": [Function],
+              "math_sqrt": [Function],
+              "math_tan": [Function],
+              "math_tanh": [Function],
+              "math_trunc": [Function],
+              "pair": [Function],
+              "parse": [Function],
+              "parse_int": [Function],
+              "prompt": [Function],
+              "raw_display": [Function],
+              "set_head": [Function],
+              "set_tail": [Function],
+              "stream": [Function],
+              "stringify": [Function],
+              "tail": [Function],
+              "tokenize": [Function],
+              "undefined": undefined,
+            },
+            "heap": Heap {
+              "storage": null,
+            },
+            "id": "-1",
+            "name": "global",
+            "tail": null,
+          },
+        },
+        "parent": EnvTreeNode {
+          "_children": Array [
+            [Circular],
+          ],
+          "environment": Object {
+            "head": Object {
+              "Infinity": Infinity,
+              "NaN": NaN,
+              "apply_in_underlying_javascript": [Function],
+              "arity": [Function],
+              "array_length": [Function],
+              "call_cc": [Function],
+              "char_at": [Function],
+              "display": [Function],
+              "display_list": [Function],
+              "draw_data": [Function],
+              "error": [Function],
+              "get_time": [Function],
+              "head": [Function],
+              "is_array": [Function],
+              "is_boolean": [Function],
+              "is_function": [Function],
+              "is_list": [Function],
+              "is_null": [Function],
+              "is_number": [Function],
+              "is_pair": [Function],
+              "is_string": [Function],
+              "is_undefined": [Function],
+              "list": [Function],
+              "math_E": 2.718281828459045,
+              "math_LN10": 2.302585092994046,
+              "math_LN2": 0.6931471805599453,
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+              "math_PI": 3.141592653589793,
+              "math_SQRT1_2": 0.7071067811865476,
+              "math_SQRT2": 1.4142135623730951,
+              "math_abs": [Function],
+              "math_acos": [Function],
+              "math_acosh": [Function],
+              "math_asin": [Function],
+              "math_asinh": [Function],
+              "math_atan": [Function],
+              "math_atan2": [Function],
+              "math_atanh": [Function],
+              "math_cbrt": [Function],
+              "math_ceil": [Function],
+              "math_clz32": [Function],
+              "math_cos": [Function],
+              "math_cosh": [Function],
+              "math_exp": [Function],
+              "math_expm1": [Function],
+              "math_floor": [Function],
+              "math_fround": [Function],
+              "math_hypot": [Function],
+              "math_imul": [Function],
+              "math_log": [Function],
+              "math_log10": [Function],
+              "math_log1p": [Function],
+              "math_log2": [Function],
+              "math_max": [Function],
+              "math_min": [Function],
+              "math_pow": [Function],
+              "math_random": [Function],
+              "math_round": [Function],
+              "math_sign": [Function],
+              "math_sin": [Function],
+              "math_sinh": [Function],
+              "math_sqrt": [Function],
+              "math_tan": [Function],
+              "math_tanh": [Function],
+              "math_trunc": [Function],
+              "pair": [Function],
+              "parse": [Function],
+              "parse_int": [Function],
+              "prompt": [Function],
+              "raw_display": [Function],
+              "set_head": [Function],
+              "set_tail": [Function],
+              "stream": [Function],
+              "stringify": [Function],
+              "tail": [Function],
+              "tokenize": [Function],
+              "undefined": undefined,
+            },
+            "heap": Heap {
+              "storage": null,
+            },
+            "id": "-1",
+            "name": "global",
+            "tail": null,
+          },
+          "parent": null,
+        },
+      },
+    },
+  },
+}
+`;
+
+exports[`apply_in_underlying_javascript works correctly and adds objects to heaps 1`] = `
+EnvTree {
+  "_root": EnvTreeNode {
+    "_children": Array [
+      EnvTreeNode {
+        "_children": Array [
+          EnvTreeNode {
+            "_children": Array [
+              EnvTreeNode {
+                "_children": Array [],
+                "environment": Object {
+                  "callExpression": Object {
+                    "arguments": Array [
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+                        "loc": undefined,
+                        "type": "Literal",
+                        "value": 0,
+                      },
+                    ],
+                    "callee": Object {
+                      "loc": SourceLocation {
+                        "end": Position {
+                          "column": 1,
+                          "line": 5,
+                        },
+                        "start": Position {
+                          "column": 0,
+                          "line": 2,
+                        },
+                      },
+                      "type": "Literal",
+                      "value": [Function],
+                    },
+                    "loc": undefined,
+                    "optional": false,
+                    "type": "CallExpression",
+                  },
+                  "head": Object {
+                    "x": 0,
+                  },
+                  "heap": Heap {
+                    "storage": Set {
+                      Array [
+                        1,
+                      ],
+                      [Function],
+                    },
+                  },
+                  "id": "50",
+                  "name": "f",
+                  "tail": Object {
+                    "head": Object {
+                      "a": Array [
+                        1,
+                      ],
+                      "f": [Function],
+                    },
+                    "heap": Heap {
+                      "storage": Set {
+                        [Function],
+                        Array [
+                          0,
+                          null,
+                        ],
+                      },
+                    },
+                    "id": "47",
+                    "name": "programEnvironment",
+                    "tail": Object {
+                      "head": Object {
+                        "$accumulate": [Function],
+                        "$append": [Function],
+                        "$build_list": [Function],
+                        "$enum_list": [Function],
+                        "$filter": [Function],
+                        "$length": [Function],
+                        "$list_to_string": [Function],
+                        "$map": [Function],
+                        "$remove": [Function],
+                        "$remove_all": [Function],
+                        "$reverse": [Function],
+                        "__access_export__": [Function],
+                        "__access_named_export__": [Function],
+                        "accumulate": [Function],
+                        "append": [Function],
+                        "build_list": [Function],
+                        "build_stream": [Function],
+                        "enum_list": [Function],
+                        "enum_stream": [Function],
+                        "equal": [Function],
+                        "eval_stream": [Function],
+                        "filter": [Function],
+                        "for_each": [Function],
+                        "integers_from": [Function],
+                        "is_stream": [Function],
+                        "length": [Function],
+                        "list_ref": [Function],
+                        "list_to_stream": [Function],
+                        "list_to_string": [Function],
+                        "map": [Function],
+                        "member": [Function],
+                        "remove": [Function],
+                        "remove_all": [Function],
+                        "reverse": [Function],
+                        "stream_append": [Function],
+                        "stream_filter": [Function],
+                        "stream_for_each": [Function],
+                        "stream_length": [Function],
+                        "stream_map": [Function],
+                        "stream_member": [Function],
+                        "stream_ref": [Function],
+                        "stream_remove": [Function],
+                        "stream_remove_all": [Function],
+                        "stream_reverse": [Function],
+                        "stream_tail": [Function],
+                        "stream_to_list": [Function],
+                      },
+                      "heap": Heap {
+                        "storage": Set {
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                          [Function],
+                        },
+                      },
+                      "id": "0",
+                      "name": "prelude",
+                      "tail": Object {
+                        "head": Object {
+                          "Infinity": Infinity,
+                          "NaN": NaN,
+                          "apply_in_underlying_javascript": [Function],
+                          "arity": [Function],
+                          "array_length": [Function],
+                          "call_cc": [Function],
+                          "char_at": [Function],
+                          "display": [Function],
+                          "display_list": [Function],
+                          "draw_data": [Function],
+                          "error": [Function],
+                          "get_time": [Function],
+                          "head": [Function],
+                          "is_array": [Function],
+                          "is_boolean": [Function],
+                          "is_function": [Function],
+                          "is_list": [Function],
+                          "is_null": [Function],
+                          "is_number": [Function],
+                          "is_pair": [Function],
+                          "is_string": [Function],
+                          "is_undefined": [Function],
+                          "list": [Function],
+                          "math_E": 2.718281828459045,
+                          "math_LN10": 2.302585092994046,
+                          "math_LN2": 0.6931471805599453,
+                          "math_LOG10E": 0.4342944819032518,
+                          "math_LOG2E": 1.4426950408889634,
+                          "math_PI": 3.141592653589793,
+                          "math_SQRT1_2": 0.7071067811865476,
+                          "math_SQRT2": 1.4142135623730951,
+                          "math_abs": [Function],
+                          "math_acos": [Function],
+                          "math_acosh": [Function],
+                          "math_asin": [Function],
+                          "math_asinh": [Function],
+                          "math_atan": [Function],
+                          "math_atan2": [Function],
+                          "math_atanh": [Function],
+                          "math_cbrt": [Function],
+                          "math_ceil": [Function],
+                          "math_clz32": [Function],
+                          "math_cos": [Function],
+                          "math_cosh": [Function],
+                          "math_exp": [Function],
+                          "math_expm1": [Function],
+                          "math_floor": [Function],
+                          "math_fround": [Function],
+                          "math_hypot": [Function],
+                          "math_imul": [Function],
+                          "math_log": [Function],
+                          "math_log10": [Function],
+                          "math_log1p": [Function],
+                          "math_log2": [Function],
+                          "math_max": [Function],
+                          "math_min": [Function],
+                          "math_pow": [Function],
+                          "math_random": [Function],
+                          "math_round": [Function],
+                          "math_sign": [Function],
+                          "math_sin": [Function],
+                          "math_sinh": [Function],
+                          "math_sqrt": [Function],
+                          "math_tan": [Function],
+                          "math_tanh": [Function],
+                          "math_trunc": [Function],
+                          "pair": [Function],
+                          "parse": [Function],
+                          "parse_int": [Function],
+                          "prompt": [Function],
+                          "raw_display": [Function],
+                          "set_head": [Function],
+                          "set_tail": [Function],
+                          "stream": [Function],
+                          "stringify": [Function],
+                          "tail": [Function],
+                          "tokenize": [Function],
+                          "undefined": undefined,
+                        },
+                        "heap": Heap {
+                          "storage": null,
+                        },
+                        "id": "-1",
+                        "name": "global",
+                        "tail": null,
+                      },
+                    },
+                  },
+                },
+                "parent": [Circular],
+              },
+            ],
+            "environment": Object {
+              "head": Object {
+                "a": Array [
+                  1,
+                ],
+                "f": [Function],
+              },
+              "heap": Heap {
+                "storage": Set {
+                  [Function],
+                  Array [
+                    0,
+                    null,
+                  ],
+                },
+              },
+              "id": "47",
+              "name": "programEnvironment",
+              "tail": Object {
+                "head": Object {
+                  "$accumulate": [Function],
+                  "$append": [Function],
+                  "$build_list": [Function],
+                  "$enum_list": [Function],
+                  "$filter": [Function],
+                  "$length": [Function],
+                  "$list_to_string": [Function],
+                  "$map": [Function],
+                  "$remove": [Function],
+                  "$remove_all": [Function],
+                  "$reverse": [Function],
+                  "__access_export__": [Function],
+                  "__access_named_export__": [Function],
+                  "accumulate": [Function],
+                  "append": [Function],
+                  "build_list": [Function],
+                  "build_stream": [Function],
+                  "enum_list": [Function],
+                  "enum_stream": [Function],
+                  "equal": [Function],
+                  "eval_stream": [Function],
+                  "filter": [Function],
+                  "for_each": [Function],
+                  "integers_from": [Function],
+                  "is_stream": [Function],
+                  "length": [Function],
+                  "list_ref": [Function],
+                  "list_to_stream": [Function],
+                  "list_to_string": [Function],
+                  "map": [Function],
+                  "member": [Function],
+                  "remove": [Function],
+                  "remove_all": [Function],
+                  "reverse": [Function],
+                  "stream_append": [Function],
+                  "stream_filter": [Function],
+                  "stream_for_each": [Function],
+                  "stream_length": [Function],
+                  "stream_map": [Function],
+                  "stream_member": [Function],
+                  "stream_ref": [Function],
+                  "stream_remove": [Function],
+                  "stream_remove_all": [Function],
+                  "stream_reverse": [Function],
+                  "stream_tail": [Function],
+                  "stream_to_list": [Function],
+                },
+                "heap": Heap {
+                  "storage": Set {
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
+                    [Function],
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+            [Circular],
+          ],
+          "environment": Object {
+            "head": Object {
+              "$accumulate": [Function],
+              "$append": [Function],
+              "$build_list": [Function],
+              "$enum_list": [Function],
+              "$filter": [Function],
+              "$length": [Function],
+              "$list_to_string": [Function],
+              "$map": [Function],
+              "$remove": [Function],
+              "$remove_all": [Function],
+              "$reverse": [Function],
+              "__access_export__": [Function],
+              "__access_named_export__": [Function],
+              "accumulate": [Function],
+              "append": [Function],
+              "build_list": [Function],
+              "build_stream": [Function],
+              "enum_list": [Function],
+              "enum_stream": [Function],
+              "equal": [Function],
+              "eval_stream": [Function],
+              "filter": [Function],
+              "for_each": [Function],
+              "integers_from": [Function],
+              "is_stream": [Function],
+              "length": [Function],
+              "list_ref": [Function],
+              "list_to_stream": [Function],
+              "list_to_string": [Function],
+              "map": [Function],
+              "member": [Function],
+              "remove": [Function],
+              "remove_all": [Function],
+              "reverse": [Function],
+              "stream_append": [Function],
+              "stream_filter": [Function],
+              "stream_for_each": [Function],
+              "stream_length": [Function],
+              "stream_map": [Function],
+              "stream_member": [Function],
+              "stream_ref": [Function],
+              "stream_remove": [Function],
+              "stream_remove_all": [Function],
+              "stream_reverse": [Function],
+              "stream_tail": [Function],
+              "stream_to_list": [Function],
+            },
+            "heap": Heap {
+              "storage": Set {
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+                [Function],
+              },
+            },
+            "id": "0",
+            "name": "prelude",
+            "tail": Object {
+              "head": Object {
+                "Infinity": Infinity,
+                "NaN": NaN,
+                "apply_in_underlying_javascript": [Function],
+                "arity": [Function],
+                "array_length": [Function],
+                "call_cc": [Function],
+                "char_at": [Function],
+                "display": [Function],
+                "display_list": [Function],
+                "draw_data": [Function],
+                "error": [Function],
+                "get_time": [Function],
+                "head": [Function],
+                "is_array": [Function],
+                "is_boolean": [Function],
+                "is_function": [Function],
+                "is_list": [Function],
+                "is_null": [Function],
+                "is_number": [Function],
+                "is_pair": [Function],
+                "is_string": [Function],
+                "is_undefined": [Function],
+                "list": [Function],
+                "math_E": 2.718281828459045,
+                "math_LN10": 2.302585092994046,
+                "math_LN2": 0.6931471805599453,
+                "math_LOG10E": 0.4342944819032518,
+                "math_LOG2E": 1.4426950408889634,
+                "math_PI": 3.141592653589793,
+                "math_SQRT1_2": 0.7071067811865476,
+                "math_SQRT2": 1.4142135623730951,
+                "math_abs": [Function],
+                "math_acos": [Function],
+                "math_acosh": [Function],
+                "math_asin": [Function],
+                "math_asinh": [Function],
+                "math_atan": [Function],
+                "math_atan2": [Function],
+                "math_atanh": [Function],
+                "math_cbrt": [Function],
+                "math_ceil": [Function],
+                "math_clz32": [Function],
+                "math_cos": [Function],
+                "math_cosh": [Function],
+                "math_exp": [Function],
+                "math_expm1": [Function],
+                "math_floor": [Function],
+                "math_fround": [Function],
+                "math_hypot": [Function],
+                "math_imul": [Function],
+                "math_log": [Function],
+                "math_log10": [Function],
+                "math_log1p": [Function],
+                "math_log2": [Function],
+                "math_max": [Function],
+                "math_min": [Function],
+                "math_pow": [Function],
+                "math_random": [Function],
+                "math_round": [Function],
+                "math_sign": [Function],
+                "math_sin": [Function],
+                "math_sinh": [Function],
+                "math_sqrt": [Function],
+                "math_tan": [Function],
+                "math_tanh": [Function],
+                "math_trunc": [Function],
+                "pair": [Function],
+                "parse": [Function],
+                "parse_int": [Function],
+                "prompt": [Function],
+                "raw_display": [Function],
+                "set_head": [Function],
+                "set_tail": [Function],
+                "stream": [Function],
+                "stringify": [Function],
+                "tail": [Function],
+                "tokenize": [Function],
+                "undefined": undefined,
+              },
+              "heap": Heap {
+                "storage": null,
+              },
+              "id": "-1",
+              "name": "global",
+              "tail": null,
+            },
+          },
+          "parent": EnvTreeNode {
+            "_children": Array [
+              [Circular],
+            ],
+            "environment": Object {
+              "head": Object {
+                "Infinity": Infinity,
+                "NaN": NaN,
+                "apply_in_underlying_javascript": [Function],
+                "arity": [Function],
+                "array_length": [Function],
+                "call_cc": [Function],
+                "char_at": [Function],
+                "display": [Function],
+                "display_list": [Function],
+                "draw_data": [Function],
+                "error": [Function],
+                "get_time": [Function],
+                "head": [Function],
+                "is_array": [Function],
+                "is_boolean": [Function],
+                "is_function": [Function],
+                "is_list": [Function],
+                "is_null": [Function],
+                "is_number": [Function],
+                "is_pair": [Function],
+                "is_string": [Function],
+                "is_undefined": [Function],
+                "list": [Function],
+                "math_E": 2.718281828459045,
+                "math_LN10": 2.302585092994046,
+                "math_LN2": 0.6931471805599453,
+                "math_LOG10E": 0.4342944819032518,
+                "math_LOG2E": 1.4426950408889634,
+                "math_PI": 3.141592653589793,
+                "math_SQRT1_2": 0.7071067811865476,
+                "math_SQRT2": 1.4142135623730951,
+                "math_abs": [Function],
+                "math_acos": [Function],
+                "math_acosh": [Function],
+                "math_asin": [Function],
+                "math_asinh": [Function],
+                "math_atan": [Function],
+                "math_atan2": [Function],
+                "math_atanh": [Function],
+                "math_cbrt": [Function],
+                "math_ceil": [Function],
+                "math_clz32": [Function],
+                "math_cos": [Function],
+                "math_cosh": [Function],
+                "math_exp": [Function],
+                "math_expm1": [Function],
+                "math_floor": [Function],
+                "math_fround": [Function],
+                "math_hypot": [Function],
+                "math_imul": [Function],
+                "math_log": [Function],
+                "math_log10": [Function],
+                "math_log1p": [Function],
+                "math_log2": [Function],
+                "math_max": [Function],
+                "math_min": [Function],
+                "math_pow": [Function],
+                "math_random": [Function],
+                "math_round": [Function],
+                "math_sign": [Function],
+                "math_sin": [Function],
+                "math_sinh": [Function],
+                "math_sqrt": [Function],
+                "math_tan": [Function],
+                "math_tanh": [Function],
+                "math_trunc": [Function],
+                "pair": [Function],
+                "parse": [Function],
+                "parse_int": [Function],
+                "prompt": [Function],
+                "raw_display": [Function],
+                "set_head": [Function],
+                "set_tail": [Function],
+                "stream": [Function],
+                "stringify": [Function],
+                "tail": [Function],
+                "tokenize": [Function],
+                "undefined": undefined,
+              },
+              "heap": Heap {
+                "storage": null,
+              },
+              "id": "-1",
+              "name": "global",
+              "tail": null,
+            },
+            "parent": null,
+          },
+        },
+      },
+    },
+  },
+}
+`;
diff --git a/src/cse-machine/__tests__/cse-machine-heap.ts b/src/cse-machine/__tests__/cse-machine-heap.ts
index 590b9f8a4..ba5ac8b9c 100644
--- a/src/cse-machine/__tests__/cse-machine-heap.ts
+++ b/src/cse-machine/__tests__/cse-machine-heap.ts
@@ -4,37 +4,45 @@ import { Chapter } from '../../types'
 import { stripIndent } from '../../utils/formatters'
 import { sourceRunner } from '../../runner'
 import Heap from '../heap'
-import { Array } from '../types'
+import { EnvArray } from '../types'
 
 test('Heap works correctly', () => {
-  const heap = new Heap()
-  expect(heap.size()).toMatchInlineSnapshot(`0`)
-  expect(heap.getHeap()).toMatchInlineSnapshot(`Set {}`)
+  const heap1 = new Heap()
+  expect(heap1.size()).toMatchInlineSnapshot(`0`)
+  expect(heap1.getHeap()).toMatchInlineSnapshot(`Set {}`)
 
-  const arr = [0] as Array
-  heap.add(arr)
-  expect(heap.contains([0] as Array)).toMatchInlineSnapshot(`false`)
-  expect(heap.contains(arr)).toMatchInlineSnapshot(`true`)
-  heap.add(arr)
-  expect(heap.size()).toMatchInlineSnapshot(`1`)
-  expect(heap.getHeap()).toMatchInlineSnapshot(`
+  const arr = [0] as EnvArray
+  const closure = mockClosure(true)
+  heap1.add(arr, closure)
+  heap1.add(arr)
+  expect(heap1.contains([0] as EnvArray)).toMatchInlineSnapshot(`false`)
+  expect(heap1.contains(arr)).toMatchInlineSnapshot(`true`)
+  expect(heap1.contains(closure)).toMatchInlineSnapshot(`true`)
+  expect(heap1.size()).toMatchInlineSnapshot(`2`)
+  expect(heap1.getHeap()).toMatchInlineSnapshot(`
     Set {
       Array [
         0,
       ],
+      [Function],
     }
   `)
 
-  const closure = mockClosure()
-  heap.add(closure)
-  expect(heap.contains(closure)).toMatchInlineSnapshot(`true`)
-  expect(heap.size()).toMatchInlineSnapshot(`2`)
-  expect(heap.getHeap()).toMatchInlineSnapshot(`
+  const heap2 = new Heap()
+  expect(heap1.move(mockClosure(true), heap2)).toMatchInlineSnapshot(`false`)
+  expect(heap1.move(arr, heap2)).toMatchInlineSnapshot(`true`)
+  expect(heap1.contains(arr)).toMatchInlineSnapshot(`false`)
+  expect(heap1.getHeap()).toMatchInlineSnapshot(`
+    Set {
+      [Function],
+    }
+  `)
+  expect(heap2.contains(arr)).toMatchInlineSnapshot(`true`)
+  expect(heap2.getHeap()).toMatchInlineSnapshot(`
     Set {
       Array [
         0,
       ],
-      [Function],
     }
   `)
 })
@@ -50,11 +58,11 @@ const expectEnvTreeFrom = (code: string, hasPrelude = true) => {
   ).resolves
 }
 
-test('Pre-defined functions are correctly added to prelude environment heap', () => {
+test('Pre-defined functions are correctly added to prelude heap', () => {
   expectEnvTreeFrom('0;').toMatchSnapshot()
 })
 
-test('Arrays and closures are correctly added to their respective environment heaps', () => {
+test('Arrays and closures are correctly added to their respective heaps', () => {
   expectEnvTreeFrom(
     stripIndent`
     function f(x) {
@@ -70,7 +78,7 @@ test('Arrays and closures are correctly added to their respective environment he
   ).toMatchSnapshot()
 })
 
-test('Arrays created from in-built functions are correctly added to the environment heap', () => {
+test('Arrays created from built-in functions are correctly added to their respective heaps', () => {
   expectEnvTreeFrom(
     stripIndent`
     pair(1, 2);
@@ -80,3 +88,26 @@ test('Arrays created from in-built functions are correctly added to the environm
     `
   ).toMatchSnapshot()
 })
+
+test('Variadic closures correctly add argument array to the function environment heap', () => {
+  expectEnvTreeFrom(
+    stripIndent`
+    const f = (...x) => x;
+    f(1, 2, 3);
+    `,
+    false
+  ).toMatchSnapshot()
+})
+
+test('apply_in_underlying_javascript works correctly and adds objects to heaps', () => {
+  expectEnvTreeFrom(
+    stripIndent`
+    let a = 0;
+    function f(x) {
+      a = [1];
+      return x => x;
+    }
+    apply_in_underlying_javascript(f, list(0));
+    `
+  ).toMatchSnapshot()
+})
diff --git a/src/cse-machine/__tests__/cse-machine-unique-id.ts b/src/cse-machine/__tests__/cse-machine-unique-id.ts
index 6c181ffb0..30ddc2023 100644
--- a/src/cse-machine/__tests__/cse-machine-unique-id.ts
+++ b/src/cse-machine/__tests__/cse-machine-unique-id.ts
@@ -5,26 +5,40 @@ import { stripIndent } from '../../utils/formatters'
 import { sourceRunner } from '../../runner'
 import { createProgramEnvironment } from '../utils'
 
-const getContextFrom = async (code: string) => {
+const getContextFrom = async (code: string, envSteps?: number) => {
   const context = mockContext(Chapter.SOURCE_4)
   const parsed = parse(code, context)
-  await sourceRunner(parsed!, context, false, { executionMethod: 'cse-machine' })
+  await sourceRunner(parsed!, context, false, { envSteps, executionMethod: 'cse-machine' })
   return context
 }
 
-test("Context runtime's objectCount continues after prelude", async () => {
+test("Program environment's id continues after prelude", async () => {
   const context = await getContextFrom('const a = list(1, 2, 3);')
-  // 1 prelude environment + 45 prelude closures in Source 4,
-  // so program environment has id of '46'
+  // 1 prelude environment + 46 prelude closures in Source 4,
+  // so program environment has id of '47'
   expect(context.runtime.environments[0].id).toMatchInlineSnapshot(`"47"`)
 })
 
 test("Context runtime's objectCount continues after prelude", async () => {
   const context = await getContextFrom('const a = list(1, 2, 3);')
-  // 1 program environment + 3 arrays from the list function, so final objectCount is 50
+  // 1 program environment + 3 arrays from the list function, so final objectCount is 51
   expect(context.runtime.objectCount).toMatchInlineSnapshot(`51`)
 })
 
+test("Context runtime's objectCount continues after apply_in_underlying_javascript call", async () => {
+  const context = await getContextFrom(
+    stripIndent`
+      function f(...x) {
+        return [x];
+      }
+      apply_in_underlying_javascript(f, list(1, 2, 3));
+    `
+  )
+  // 1 program environment + 1 closure + 1 function environment
+  // 3 arrays from list + 1 array from variadic argument + 1 array from from function result
+  expect(context.runtime.objectCount).toMatchInlineSnapshot(`55`)
+})
+
 test('Every environment/array/closure has a unique id', async () => {
   const context = await getContextFrom(
     stripIndent`
@@ -43,62 +57,56 @@ test('Every environment/array/closure has a unique id', async () => {
   expect(context.runtime.environmentTree).toMatchSnapshot()
   // Environments: 1 prelude + 1 program + 1 function (c) + 1 block, total: 4
   // Arrays: 4 arrays created manually + 4 arrays from in-built functions (pair, list), total: 8
-  // Closures: 45 prelude closures + 1 closure in program (c) + 1 closure in block, total 47
-  // Total count: 4 + 8 + 47 = 59
+  // Closures: 46 prelude closures + 1 closure in program (c) + 1 closure in block, total 48
+  // Total count: 4 + 8 + 48 = 60
   expect(context.runtime.objectCount).toMatchInlineSnapshot(`60`)
 })
 
 test('CSE Machine stops at the given step number', async () => {
-  const parsed = parse(
+  const context = await getContextFrom(
     stripIndent`
       let x = 0;
       for (let i = 0; i < 10; i = i + 1) {
         x = [x];
       }
     `,
-    mockContext(Chapter.SOURCE_4)
+    100
   )
-  // The above program has a total of 335 steps
-  // Start from steps = 1 so that the program environment always exists
-  for (let steps = 1; steps < 336; steps++) {
-    const context = mockContext(Chapter.SOURCE_4)
-    await sourceRunner(parsed!, context, false, { envSteps: steps, executionMethod: 'cse-machine' })
-    // A simple check to ensure that the the CSE Machine does indeed stop at the given step number
-    if (steps === 100) {
-      // 7 additional environments + 2 arrays created, so object count is 47 + 7 + 2 = 56
-      expect(context.runtime.objectCount).toMatchInlineSnapshot(`57`)
-    }
-  }
+  // 7 additional environments + 2 arrays created at step 100, so object count is 48 + 7 + 2 = 57
+  expect(context.runtime.objectCount).toMatchInlineSnapshot(`57`)
 })
 
-const mockProgramEnv = createProgramEnvironment(mockContext(), false)
+const programEnvName = createProgramEnvironment(mockContext(), false).name
 
 const getProgramEnv = (context: Context) => {
   let env: Environment | null = context.runtime.environments[0]
-  while (env && env.name !== mockProgramEnv.name) {
+  while (env && env.name !== programEnvName) {
     env = env.tail
   }
   return env
 }
 
-const parsed = parse(
-  stripIndent`
-      let x = 0;
-      for (let i = 0; i < 10; i = i + 1) {
-        x = [x];
-      }
-    `,
-  mockContext(Chapter.SOURCE_4)
-)
-// The above program has a total of 335 steps
-// Start from steps = 1 so that the program environment always exists
 test('Program environment id stays the same regardless of amount of steps', async () => {
-  let same = true
+  const parsed = parse(
+    stripIndent`
+        let x = 0;
+        for (let i = 0; i < 10; i = i + 1) {
+          x = [x];
+        }
+      `,
+    mockContext(Chapter.SOURCE_4)
+  )
+  let programEnvId = '47'
+  // The above program has a total of 335 steps
+  // Start from steps = 1 so that the program environment always exists
   for (let steps = 1; steps < 336; steps++) {
     const context = mockContext(Chapter.SOURCE_4)
     await sourceRunner(parsed!, context, false, { envSteps: steps, executionMethod: 'cse-machine' })
-    const programEnv = getProgramEnv(context)
-    same &&= programEnv!.id === `"46"`
+    const programEnv = getProgramEnv(context)!
+    if (programEnv.id !== programEnvId) {
+      programEnvId = programEnv.id
+      break
+    }
   }
-  expect(same).toMatchInlineSnapshot(`false`)
+  expect(programEnvId).toMatchInlineSnapshot(`"47"`)
 })
diff --git a/src/cse-machine/closure.ts b/src/cse-machine/closure.ts
new file mode 100644
index 000000000..42084e07a
--- /dev/null
+++ b/src/cse-machine/closure.ts
@@ -0,0 +1,152 @@
+import { generate } from 'astring'
+import * as es from 'estree'
+
+import {
+  currentEnvironment,
+  hasReturnStatement,
+  isBlockStatement,
+  isStatementSequence,
+  uniqueId
+} from '../cse-machine/utils'
+import { Context, Environment, StatementSequence, Value } from '../types'
+import * as ast from '../utils/ast/astCreator'
+import { Control, Stash, generateCSEMachineStateStream } from './interpreter'
+import { envInstr } from './instrCreator'
+
+const closureToJS = (value: Closure, context: Context) => {
+  function DummyClass(this: Closure) {
+    const args: Value[] = [...arguments]
+    const node = ast.callExpression(
+      ast.literal(value as any, value.node.loc),
+      args.map(arg => ast.primitive(arg))
+    )
+    // Create a new CSE Machine with the same context as the current one, but with
+    // the control reset to only contain the call expression, and the stash emptied.
+    const newContext = { ...context, runtime: { ...context.runtime, debuggerOn: false } }
+    newContext.runtime.control = new Control()
+    // Also need the env instruction to return back to the current environment at the end.
+    // The call expression won't create one as there is only one item in the control.
+    newContext.runtime.control.push(envInstr(currentEnvironment(context), node), node)
+    newContext.runtime.stash = new Stash()
+    const gen = generateCSEMachineStateStream(
+      newContext,
+      newContext.runtime.control,
+      newContext.runtime.stash,
+      -1,
+      -1
+    )
+    // Run the new CSE Machine fully to obtain the result in the stash
+    for (const _ of gen) {
+    }
+    // Also don't forget to update object count in original context
+    context.runtime.objectCount = newContext.runtime.objectCount
+    return newContext.runtime.stash.peek()
+  }
+  Object.defineProperty(DummyClass, 'name', {
+    value: value.functionName
+  })
+  Object.setPrototypeOf(DummyClass, () => undefined)
+  Object.defineProperty(DummyClass, 'Inherits', {
+    value: (Parent: Value) => {
+      DummyClass.prototype = Object.create(Parent.prototype)
+      DummyClass.prototype.constructor = DummyClass
+    }
+  })
+  DummyClass.toString = () => generate(value.originalNode)
+  DummyClass.call = (thisArg: Value, ...args: Value[]): any => {
+    return DummyClass.apply(thisArg, args)
+  }
+  return DummyClass
+}
+
+class Callable extends Function {
+  constructor(f: any) {
+    super()
+    return Object.setPrototypeOf(f, new.target.prototype)
+  }
+}
+
+/**
+ * Models function value in the CSE machine.
+ */
+export default class Closure extends Callable {
+  public static makeFromArrowFunction(
+    node: es.ArrowFunctionExpression,
+    environment: Environment,
+    context: Context,
+    dummyReturn?: boolean,
+    predefined?: boolean
+  ) {
+    const functionBody: es.BlockStatement | StatementSequence =
+      !isBlockStatement(node.body) && !isStatementSequence(node.body)
+        ? ast.blockStatement([ast.returnStatement(node.body, node.body.loc)], node.body.loc)
+        : dummyReturn && !hasReturnStatement(node.body)
+        ? ast.blockStatement(
+            [
+              ...node.body.body,
+              ast.returnStatement(ast.identifier('undefined', node.body.loc), node.body.loc)
+            ],
+            node.body.loc
+          )
+        : node.body
+
+    const closure = new Closure(
+      ast.blockArrowFunction(node.params as es.Identifier[], functionBody, node.loc),
+      environment,
+      context,
+      predefined
+    )
+
+    // Set the closure's node to point back at the original one
+    closure.originalNode = node
+
+    return closure
+  }
+
+  /** Unique ID defined for closure */
+  public readonly id: string
+
+  /** Name of the constant declaration that the closure is assigned to */
+  public declaredName?: string
+
+  /** String representation of the closure, e.g. `x => ...` */
+  public functionName: string
+
+  /** Fake closure function */
+  public fun: Function
+
+  /** Keeps track of whether the closure is a pre-defined function */
+  public predefined: boolean
+
+  /** The original node that created this Closure */
+  public originalNode: es.Function
+
+  constructor(
+    public node: es.ArrowFunctionExpression,
+    public environment: Environment,
+    context: Context,
+    isPredefined?: boolean
+  ) {
+    super(function (this: any, ...args: any[]) {
+      return funJS.apply(this, args)
+    })
+    this.originalNode = node
+    this.id = uniqueId(context)
+    currentEnvironment(context).heap.add(this)
+    const params = this.node.params.map((o: es.Identifier | es.RestElement) =>
+      o.type === 'RestElement' ? '...' + (o.argument as es.Identifier).name : o.name
+    )
+    this.functionName = params.join(', ')
+    if (params.length !== 1 || params[0].startsWith('...')) {
+      this.functionName = '(' + this.functionName + ')'
+    }
+    this.functionName += ' => ...'
+    const funJS = closureToJS(this, context)
+    this.fun = funJS
+    this.predefined = isPredefined ?? false
+  }
+
+  public toString(): string {
+    return generate(this.originalNode)
+  }
+}
diff --git a/src/cse-machine/heap.ts b/src/cse-machine/heap.ts
index f74e3cbaa..09b4887ec 100644
--- a/src/cse-machine/heap.ts
+++ b/src/cse-machine/heap.ts
@@ -15,16 +15,30 @@ export default class Heap {
     }
   }
 
+  /** Checks the existence of `item` in the heap. */
   contains(item: any): boolean {
     return this.storage?.has(item) ?? false
   }
 
+  /** Gets the number of items in the heap. */
   size(): number {
     return this.storage?.size ?? 0
   }
 
+  /**
+   * Removes `item` from current heap and adds it to `otherHeap`.
+   * If the current heap does not contain `item`, nothing happens.
+   * @returns whether the item transfer is successful
+   */
+  move(item: HeapObject, otherHeap: Heap): boolean {
+    if (!this.contains(item)) return false
+    this.storage!.delete(item)
+    otherHeap.add(item)
+    return true
+  }
+
+  /** Returns a copy of the heap's contents. */
   getHeap(): Set<HeapObject> {
-    // return a copy of the heap's contents
     return new Set(this.storage)
   }
 }
diff --git a/src/cse-machine/interpreter.ts b/src/cse-machine/interpreter.ts
index 2cb8ea637..a7f3f6a7f 100644
--- a/src/cse-machine/interpreter.ts
+++ b/src/cse-machine/interpreter.ts
@@ -7,13 +7,12 @@
 
 /* tslint:disable:max-classes-per-file */
 import * as es from 'estree'
-import { isArray, reverse } from 'lodash'
+import { isArray, isFunction, reverse } from 'lodash'
 
 import { IOptions } from '..'
 import { UNKNOWN_LOCATION } from '../constants'
 import * as errors from '../errors/errors'
 import { RuntimeSourceError } from '../errors/runtimeSourceError'
-import Closure from '../interpreter/closure'
 import { checkEditorBreakpoints } from '../stdlib/inspector'
 import { Context, ContiguousArrayElements, Result, type StatementSequence, Value } from '../types'
 import * as ast from '../utils/ast/astCreator'
@@ -33,6 +32,7 @@ import {
   makeDummyContCallExpression
 } from './continuations'
 import * as instr from './instrCreator'
+import { Stack } from './stack'
 import {
   AppInstr,
   ArrLitInstr,
@@ -71,6 +71,7 @@ import {
   hasDeclarations,
   hasImportDeclarations,
   isBlockStatement,
+  isEnvArray,
   isInstr,
   isNode,
   isSimpleFunction,
@@ -78,9 +79,9 @@ import {
   pushEnvironment,
   reduceConditional,
   setVariable,
-  Stack,
   valueProducing
 } from './utils'
+import Closure from './closure'
 
 type CmdEvaluator = (
   command: ControlItem,
@@ -735,7 +736,6 @@ const cmdEvaluators: { [type: string]: CmdEvaluator } = {
     stash: Stash,
     isPrelude: boolean
   ) {
-    // Reuses the Closure data structure from legacy interpreter
     const closure: Closure = Closure.makeFromArrowFunction(
       command,
       currentEnvironment(context),
@@ -743,7 +743,6 @@ const cmdEvaluators: { [type: string]: CmdEvaluator } = {
       true,
       isPrelude
     )
-    currentEnvironment(context).heap.add(closure)
     stash.push(closure)
   },
 
@@ -947,11 +946,6 @@ const cmdEvaluators: { [type: string]: CmdEvaluator } = {
       // Check for number of arguments mismatch error
       checkNumberOfArguments(context, func, args, command.srcNode)
 
-      // Display the pre-defined functions on the global environment if needed.
-      if (func.preDefined) {
-        context.runtime.environments[1].heap.add(func)
-      }
-
       const next = control.peek()
 
       // Push ENVIRONMENT instruction if needed - if next control stack item
@@ -986,17 +980,37 @@ const cmdEvaluators: { [type: string]: CmdEvaluator } = {
       return
     }
 
-    // Value is a function
+    // Value is a built-in function
     // Check for number of arguments mismatch error
     checkNumberOfArguments(context, func, args, command.srcNode)
     // Directly stash result of applying pre-built functions without the CSE machine.
     try {
       const result = func(...args)
-      // Attach array properties and add to heap for any arrays created from built-in functions,
-      // examples: pair, list
-      if (isArray(result)) {
-        handleArrayCreation(context, result)
+
+      // Recursively adds `environment` and `id` properties to any arrays created,
+      // and also adds them to the heap starting from the arrays that are more deeply nested.
+      const attachEnvToResult = (value: any) => {
+        // Built-in functions don't instantly create arrays with circular references, so
+        // there is no need to keep track of visited arrays.
+        if (isArray(value) && !isEnvArray(value)) {
+          for (const item of value) {
+            attachEnvToResult(item)
+          }
+          handleArrayCreation(context, value)
+        } else if (isFunction(value) && !{}.hasOwnProperty.call(value, 'environment')) {
+          // This is a special case for the `stream` built-in function, since it returns pairs
+          // whose last element is a function. The CSE machine on the frontend will still draw
+          // these functions like closures, and the tail of the "closures" will need to point
+          // to where `stream` was called.
+          //
+          // TODO: remove this condition if `stream` becomes a pre-defined function
+          Object.defineProperties(value, {
+            environment: { value: currentEnvironment(context), writable: true }
+          })
+        }
       }
+      attachEnvToResult(result)
+
       stash.push(result)
     } catch (error) {
       if (!(error instanceof RuntimeSourceError || error instanceof errors.ExceptionError)) {
diff --git a/src/cse-machine/stack.ts b/src/cse-machine/stack.ts
new file mode 100644
index 000000000..00dacce31
--- /dev/null
+++ b/src/cse-machine/stack.ts
@@ -0,0 +1,58 @@
+/**
+ * Stack is implemented for control and stash registers.
+ */
+interface IStack<T> {
+  push(...items: T[]): void
+  pop(): T | undefined
+  peek(): T | undefined
+  size(): number
+  isEmpty(): boolean
+  getStack(): T[]
+}
+
+export class Stack<T> implements IStack<T> {
+  // Bottom of the array is at index 0
+  private storage: T[] = []
+
+  public constructor() {}
+
+  public push(...items: T[]): void {
+    for (const item of items) {
+      this.storage.push(item)
+    }
+  }
+
+  public pop(): T | undefined {
+    return this.storage.pop()
+  }
+
+  public peek(): T | undefined {
+    if (this.isEmpty()) {
+      return undefined
+    }
+    return this.storage[this.size() - 1]
+  }
+
+  public size(): number {
+    return this.storage.length
+  }
+
+  public isEmpty(): boolean {
+    return this.size() == 0
+  }
+
+  public getStack(): T[] {
+    // return a copy of the stack's contents
+    return [...this.storage]
+  }
+
+  public some(predicate: (value: T) => boolean): boolean {
+    return this.storage.some(predicate)
+  }
+
+  // required for first-class continuations,
+  // which directly mutate this stack globally.
+  public setTo(otherStack: Stack<T>): void {
+    this.storage = otherStack.storage
+  }
+}
diff --git a/src/cse-machine/types.ts b/src/cse-machine/types.ts
index 89b2a09a1..e613cdd26 100644
--- a/src/cse-machine/types.ts
+++ b/src/cse-machine/types.ts
@@ -1,7 +1,7 @@
 import * as es from 'estree'
 
-import Closure from '../interpreter/closure'
 import { Environment, Node } from '../types'
+import Closure from './closure'
 
 export enum InstrType {
   RESET = 'Reset',
@@ -96,13 +96,13 @@ export type Instr =
 export type ControlItem = Node | Instr
 
 // Every array also has the properties `id` and `environment` for use in the frontend CSE Machine
-export type Array = any[] & {
+export type EnvArray = any[] & {
   readonly id: string
   environment: Environment
 }
 
 // Objects in the heap can only store arrays or closures
-export type HeapObject = Array | Closure
+export type HeapObject = EnvArray | Closure
 
 // Special class that cannot be found on the stash so is safe to be used
 // as an indicator of a breakpoint from running the CSE machine
diff --git a/src/cse-machine/utils.ts b/src/cse-machine/utils.ts
index 88d811482..0792d3197 100644
--- a/src/cse-machine/utils.ts
+++ b/src/cse-machine/utils.ts
@@ -4,73 +4,14 @@ import { isArray } from 'lodash'
 import { Context } from '..'
 import * as errors from '../errors/errors'
 import { RuntimeSourceError } from '../errors/runtimeSourceError'
-import Closure from '../interpreter/closure'
 import type { Environment, Node, StatementSequence, Value } from '../types'
 import * as ast from '../utils/ast/astCreator'
 import { isContinuation } from './continuations'
 import Heap from './heap'
 import * as instr from './instrCreator'
 import { Control } from './interpreter'
-import { AppInstr, Array, ControlItem, Instr, InstrType } from './types'
-
-/**
- * Stack is implemented for control and stash registers.
- */
-interface IStack<T> {
-  push(...items: T[]): void
-  pop(): T | undefined
-  peek(): T | undefined
-  size(): number
-  isEmpty(): boolean
-  getStack(): T[]
-}
-
-export class Stack<T> implements IStack<T> {
-  // Bottom of the array is at index 0
-  private storage: T[] = []
-
-  public constructor() {}
-
-  public push(...items: T[]): void {
-    for (const item of items) {
-      this.storage.push(item)
-    }
-  }
-
-  public pop(): T | undefined {
-    return this.storage.pop()
-  }
-
-  public peek(): T | undefined {
-    if (this.isEmpty()) {
-      return undefined
-    }
-    return this.storage[this.size() - 1]
-  }
-
-  public size(): number {
-    return this.storage.length
-  }
-
-  public isEmpty(): boolean {
-    return this.size() == 0
-  }
-
-  public getStack(): T[] {
-    // return a copy of the stack's contents
-    return [...this.storage]
-  }
-
-  public some(predicate: (value: T) => boolean): boolean {
-    return this.storage.some(predicate)
-  }
-
-  // required for first-class continuations,
-  // which directly mutate this stack globally.
-  public setTo(otherStack: Stack<T>): void {
-    this.storage = otherStack.storage
-  }
-}
+import { AppInstr, EnvArray, ControlItem, Instr, InstrType } from './types'
+import Closure from './closure'
 
 /**
  * Typeguard for Instr to distinguish between program statements and instructions.
@@ -162,47 +103,36 @@ export const uniqueId = (context: Context): string => {
   return `${context.runtime.objectCount++}`
 }
 
-/**
- * Helper function for `handleArrayCreation`, with an extra argument: `visited`.
- *
- * @param context the context used to provide the current environment and new unique id
- * @param array the array to add the properties to, and to add to the current environment heap to
- * @param visited a set of arrays which are already handled before,
- *                used to keep track of circular references
- */
-const arrayCreationHelper = (context: Context, array: any[], visited: Set<any[]>): void => {
-  if (visited.has(array) || array.hasOwnProperty('id')) {
-    return
-  }
-  visited.add(array)
-  // Nested arrays are always created first, so outer arrays are handled after nested ones
-  // to preserve creation order in the environment heap
-  for (const item of array) {
-    if (isArray(item)) {
-      arrayCreationHelper(context, item, visited)
-    }
-  }
-  // Properties are defined this way to prevent them from being enumerable
-  Object.defineProperties(array, {
-    id: { value: uniqueId(context) },
-    // Make environment writable as there are still cases where the frontend might need to
-    // change the environment of an array, like when the prelude environment is merged
-    // into the global environment in the visualisation of the CSE Machine
-    environment: { value: currentEnvironment(context), writable: true }
-  })
-  currentEnvironment(context).heap.add(array as Array)
+export const isEnvArray = (item: any): item is EnvArray => {
+  return (
+    isArray(item) &&
+    {}.hasOwnProperty.call(item, 'id') &&
+    {}.hasOwnProperty.call(item, 'environment')
+  )
 }
 
 /**
  * Adds the properties `id` and `environment` to the given array, and adds the array to the
- * current environment's heap. Recursively does this for any nested arrays first, before
- * handling the current one.
+ * current environment's heap. Adds the array to the heap of `envOverride` instead if it's defined.
  *
  * @param context the context used to provide the current environment and new unique id
- * @param array the array to add the properties to, and to add to the current environment heap to
+ * @param array the array to attach properties to, and for addition to the heap
  */
-export const handleArrayCreation = (context: Context, array: any[]): void => {
-  arrayCreationHelper(context, array, new Set<any[]>())
+export const handleArrayCreation = (
+  context: Context,
+  array: any[],
+  envOverride?: Environment
+): void => {
+  const environment = envOverride ?? currentEnvironment(context)
+  // Both id and environment are non-enumerable so iterating
+  // through the array will not return these values
+  Object.defineProperties(array, {
+    id: { value: uniqueId(context) },
+    // Make environment writable as there are cases on the frontend where
+    // environments of objects need to be modified
+    environment: { value: environment, writable: true }
+  })
+  environment.heap.add(array as EnvArray)
 }
 
 /**
@@ -325,7 +255,9 @@ export const createEnvironment = (
   callExpression: es.CallExpression
 ): Environment => {
   const environment: Environment = {
-    name: isIdentifier(callExpression.callee) ? callExpression.callee.name : closure.functionName,
+    name: isIdentifier(callExpression.callee)
+      ? callExpression.callee.name
+      : closure.declaredName ?? closure.functionName,
     tail: closure.environment,
     head: {},
     heap: new Heap(),
@@ -337,7 +269,9 @@ export const createEnvironment = (
   }
   closure.node.params.forEach((param, index) => {
     if (isRestElement(param)) {
-      environment.head[(param.argument as es.Identifier).name] = args.slice(index)
+      const array = args.slice(index)
+      handleArrayCreation(context, array, environment)
+      environment.head[(param.argument as es.Identifier).name] = array
     } else {
       environment.head[(param as es.Identifier).name] = args[index]
     }
@@ -466,6 +400,10 @@ export function defineVariable(
     return handleRuntimeError(context, new errors.VariableRedeclaration(node, name, !constant))
   }
 
+  if (constant && value instanceof Closure) {
+    value.declaredName = name
+  }
+
   Object.defineProperty(environment.head, name, {
     value,
     writable: !constant,
diff --git a/src/mocks/context.ts b/src/mocks/context.ts
index 30e59780b..7e19650ad 100644
--- a/src/mocks/context.ts
+++ b/src/mocks/context.ts
@@ -1,7 +1,8 @@
 import * as es from 'estree'
 
 import createContext, { EnvTree } from '../createContext'
-import Closure from '../interpreter/closure'
+import OldClosure from '../interpreter/closure'
+import Closure from '../cse-machine/closure'
 import { createBlockEnvironment } from '../interpreter/interpreter'
 import { Chapter, Context, Environment, Variant } from '../types'
 
@@ -63,19 +64,21 @@ export function mockRuntimeContext(): Context {
   return context
 }
 
-export function mockClosure(): Closure {
+export function mockClosure(cseMachineClosure: true): Closure
+export function mockClosure(cseMachineClosure?: false): OldClosure
+export function mockClosure(cseMachineClosure?: boolean): Closure | OldClosure {
   const context = createContext()
-  return new Closure(
+  return new (cseMachineClosure ? Closure : OldClosure)(
     {
-      type: 'FunctionExpression',
+      type: 'ArrowFunctionExpression',
+      expression: true,
       loc: null,
-      id: null,
       params: [],
       body: {
         type: 'BlockStatement',
         body: []
       }
-    } as es.FunctionExpression,
+    } as es.ArrowFunctionExpression,
     mockEnvironment(context),
     context
   )