#3696: Incorrect type inferred with -fwarn-missing-signatures and a type class
---------------------------------+------------------------------------------
Reporter: spl | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler (Type checker)
Version: 6.10.1 | Keywords:
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: Incorrect warning at
compile-time
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The inferred type using -fwarn-missing-signatures and a type class is too
general for top-level values.
Here is a simplified example:
{{{
{-# OPTIONS -Wall #-}
class C a where c :: a
instance C Int where c = 37
def = c
use :: Int
use = def
}}}
The inferred type reported by GHCi when -fwarn-missing-signatures is
enabled is:
{{{
Ex.hs:7:0:
Warning: Definition but no type signature for `def'
Inferred type: def :: a
}}}
The most general possible type here is {{{C a => a}}}. When asking GHCi
for the type of {{{def}}}, it reports {{{Int}}}.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3696>
GHC <http://www.haskell.org/ghc/>
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