#1813: Strange type representation bug with phantom type synonyms in interactive
mode
----------------------+-----------------------------------------------------
Reporter: guest | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: GHCi | Version: 6.9
Severity: normal | Keywords:
Difficulty: Unknown | Os: Unknown
Testcase: | Architecture: Unknown
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Sorry for the confusing summary
The following module defines a phatom type synonym and a simple function
{{{
module Phantom where
type PhantomSyn a = Int
f = (\_ -> 2) :: PhantomSyn a -> Int
}}}
When running in interactive mode (the bug doesn't seem to be reproducible
otherwise) the typechecker gives a strange error
{{{
./ghc-inplace --interactive /tmp/Phantom.hs
GHCi, version 6.9.20071025: http://www.haskell.org/ghc/ :? for help
Loading package base ... linking ... done.
[1 of 1] Compiling Phantom ( /tmp/Phantom.hs, interpreted )
Ok, modules loaded: Phantom.
*Phantom> f "incorrectParam"
<interactive>:1:2:
Couldn't match expected type `PhantomSyn GHC.Prim.Any'
against inferred type `[Char]'
Expected type: PhantomSyn GHC.Prim.Any
Inferred type: [Char]
In the first argument of `f', namely `"incorrectParam"'
In the expression: f "incorrectParam"
}}}
The typechecker should output
{{{
Expected type: PhantomSyn a
}}}
If I skip the interactive mode (including the erroneous declaration in the
Phantom.hs itself) or I define f as
{{{
f :: PhantomSyn a -> Int
f = (\_ -> 2)
}}}
The incorrect error report disappears.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1813>
GHC <http://www.haskell.org/ghc/>
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