Difference between revisions of "Untypeable Haskell 98"
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DonStewart (talk | contribs) (categorise) |
Tomjaguarpaw (talk | contribs) (Deleting page that hasn't been updated for over 10 years) |
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| − | Here we document code that looks like it should be valid Haskell98, but |
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| − | isn't typeable without extensions: |
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| − | <haskell> |
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| − | f :: a -> a |
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| − | f x = g x |
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| − | where |
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| − | -- g :: a -> a |
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| − | g y = bind x y |
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| − | |||
| − | bind :: a -> a -> a |
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| − | bind a b = a |
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| − | </haskell> |
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| − | The above Haskell code is Haskell 98, rank-1 types, but cannot be given a type signature. Try commenting out the type signature for g and everything will go wrong. |
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| − | In GHC making the type of f :: forall a . a -> a, and adding -fglasgow-exts will make this code work. No such luck in Hugs. |
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| − | With pattern type annotations, however, the code works in both Hugs and GHC: |
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| − | <haskell> |
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| − | f :: a -> a |
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| − | f (x :: a) = g x |
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| − | where |
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| − | g :: a -> a |
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| − | g y = bind x y |
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| − | |||
| − | bind :: a -> a -> a |
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| − | bind a b = a |
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| − | </haskell> |
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| − | |||
| − | [[Category:Proposals]] |
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