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  • #6022

Closed
Open
Opened Apr 19, 2012 by Simon Peyton Jones@simonpjDeveloper

GHC infers over-general types

Consider

f x = x + head

GHC will (with no flags) will compile this almost-certainly-wrong program, giving f the type

    f :: forall a. Num ([a] -> a) => ([a] -> a) -> [a] -> a

There's nothing wrong with that type, and in principle someone might later define a suitable instance of Num, but (a) it's not Haskell 98, and (b) it's unlikely to be right, so we've deferred a type error from the definition site of f to the (perhaps much later) call site.

I think GHC should complain, and require a type signature if that's what you really want. This came up on Stackoverflow

Trac metadata
Trac field Value
Version 7.4.1
Type Bug
TypeOfFailure OtherFailure
Priority high
Resolution Unresolved
Component Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture
Assignee
Assign to
7.10.1
Milestone
7.10.1 (Past due)
Assign milestone
Time tracking
None
Due date
None
Reference: ghc/ghc#6022