|
|
| Line 1: |
Line 1: |
| − | Here we document code that looks like it should be valid Haskell98, but
| |
| − | isn't typeable without extensions:
| |
| | | | |
| − | <haskell>
| |
| − | f :: a -> a
| |
| − | f x = g x
| |
| − | where
| |
| − | -- g :: a -> a
| |
| − | g y = bind x y
| |
| − |
| |
| − | bind :: a -> a -> a
| |
| − | bind a b = a
| |
| − | </haskell>
| |
| − |
| |
| − | 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.
| |
| − |
| |
| − | 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.
| |
| − |
| |
| − | With pattern type annotations, however, the code works in both Hugs and GHC:
| |
| − |
| |
| − | <haskell>
| |
| − | f :: a -> a
| |
| − | f (x :: a) = g x
| |
| − | where
| |
| − | g :: a -> a
| |
| − | g y = bind x y
| |
| − |
| |
| − | bind :: a -> a -> a
| |
| − | bind a b = a
| |
| − | </haskell>
| |
| − |
| |
| − | [[Category:Proposals]]
| |