signatures are too permissive
ghc should reject the following (accidentally mistyped) signature, unless -XFlexibleContexts
is used.
flex :: Int -> Show a => a -> String
flex i a = show a ++ show i
hugs and ghc version below 7 rejected this correctly:
All of the type variables in the constraint `Show a'
are already in scope (at least one must be universally quantified here)
(Use -XFlexibleContexts to lift this restriction)
In the type signature for `flex':
flex :: Int -> (Show a) => a -> String
It is not Haskell98 nor Haskell2010 (I believe).
Trac metadata
Trac field | Value |
---|---|
Version | 7.4.1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler (Type checker) |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |