#4499: "skolem type variable" is bad for usability (and beginners)
----------------------------------------+-----------------------------------
Reporter: guest | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler (Type checker) | Version: 7.0.1
Keywords: skolem | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
----------------------------------------+-----------------------------------
Comment(by simonpj):
For this porgram
{{{
{-# LANGUAGE RankNTypes #-}
module Foo where
f :: (forall a. a->a) -> Int
f = error "urk"
g x = f (\v -> x)
}}}
currently we get
{{{
Foo.hs:8:7:
Couldn't match type `t' with `a'
because this skolem type variable would escape: `a'
This skolem is bound by the polymorphic type `forall a. a -> a'
The following variables have types that mention t
x :: t (bound at Foo.hs:8:3)
...
}}}
what about
{{{
Couldn't match type `t' with `a'
because the type variable 'a' would escape its scope
The (rigid, skolem) type variable 'a' is is bound by
the polymorphic type `forall a. a -> a'
The following variables have types that mention t
x :: t (bound at Foo.hs:8:3)}}}
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4499#comment:3>
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
