#3700: Being instance of Monoid is not checked
----------------------------------------+-----------------------------------
Reporter: boris | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler (Type checker) | Version: 6.10.3
Resolution: | Keywords: Monoid, Writer
Os: Windows | Testcase:
Architecture: x86 | Failure: Other
----------------------------------------+-----------------------------------
Comment (by rwbarton):
I don't think this is a bug. GHCi should accept the first declaration
because later (say in another module) someone might define an instance
`Monoid ((a -> b) -> [a] -> [b])` and then want to call the function `f`.
The second declaration is rejected due to the monomorphism restriction:
since `f` is not defined via a function binding, GHCi must choose a
monomorphic type for `f` immediately and it has no way to satisfy the
`Monoid` instance. If you turn off the monomorphism restriction by
entering `:set -XNoMonomorphismRestriction`, you will find that both
definitions are accepted.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3700#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
_______________________________________________
Glasgow-haskell-bugs mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
