Generic instance based on ISO 8601 representation #19
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| @@ -36,11 +37,18 @@ foreign import data JSDate :: * | |||
| -- | modules. | |||
| newtype Date = DateTime JSDate | |||
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| instance genericDate :: Generic Date where | |||
| toSpine d = SString (runFn2 jsDateMethod "toISOString" (toJSDate d)) | |||
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This instance doesn't represent what a Date actually is at runtime, so it's an invalid instance. Foreign data types can't have generic instances for this reason.
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So valid instances of Generic have the true representation and not just an isomorphism? That makes sense. I can close the PR if it's nonsensical.
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Yes exactly. If we allowed this, then things like everywhere would apply functions of Strings to Dates which would be bad. This is why it's recommended to derive generic instances, because they're so hard to get right by hand :)
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Ooh, I see! Thanks for the clarification :)
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Thanks for looking at this though. A newtype around String with a smart constructor might be a good way to handle this if a Generic instance is needed for some reason.
This is something I'm really wanting in my own application. I can newtype around, but this seems suitably useful and general that it might want to be included in the date definition.
Another useful instance would be
IsForeign-- I can implement and make a PR for that if wanted :)