Add more CycleInDeclaration examples - #333
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| Type class instance for recursive data type: | ||
| ```purs | ||
| data Chain a | ||
| = End a | ||
| | Link a (Chain a) | ||
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| derive instance genericChain :: Generic (Chain a) _ | ||
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| -- This builds, but blows-up call stack and triggers a | ||
| -- "too much recursion error". | ||
| instance showChain :: Show a => Show (Chain a) where | ||
| show = genericShow | ||
| {- | ||
| Fix the issue by replacing the above line with: | ||
| show c = genericShow c | ||
| -} | ||
| ``` | ||
| https://try.purescript.org/?gist=32b78ce065d60427620cdd8d40777a1f |
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Perhaps this could just be a link to the contents being added in #338?
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| ### Additional Examples | ||
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| Mutually recursive functions: |
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If we move the generic deriving example to be a link then we can change this header to be ### Mutual recursion and just focus on this mutual recursion example. I think that fits better with how other errors use the Notes section.
Also, what do you think of trimming the example a little bit to something like this?
isEven :: Int -> Boolean
isEven n
| n == 0 = true
| otherwise = again (n - 1)
again :: Int -> Boolean
again = isEvenwhich also fails, producing this error:
The value of isEven is undefined here, so this reference is not allowed. while checking that expression isEven has type Int -> Boolean in binding group isEven, again
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This PR hasn't been merged because I'm not sure that should be in the Getting Started section if it's in reference to the Book. Shouldn't the Book clarify that instead? (wrong PR) This PR hasn't been merged because while this is about the CycleInDeclaration, it's really explaining places where eta-expansion is needed. However, it doesn't clarify why. So, I feel like it's incomplete. |
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I found the x = x example a bit too minimal to figure out what's required to fix these errors.