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  • #3696

Closed
Open
Opened Nov 26, 2009 by spl@trac-spl

Incorrect type inferred with -fwarn-missing-signatures and a type class

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.

Trac metadata
Trac field Value
Version 6.10.1
Type Bug
TypeOfFailure OtherFailure
Priority normal
Resolution Unresolved
Component Compiler (Type checker)
Test case
Differential revisions
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Blocking
CC leather@cs.uu.nl
Operating system
Architecture
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Reference: ghc/ghc#3696