#5380: Too general type with Arrows extension
-------------------------------+--------------------------------------------
Reporter: sebf | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.0.3 | Keywords:
Testcase: | Blockedby:
Os: Linux | Blocking:
Architecture: x86_64 (amd64) | Failure: GHC accepts invalid program
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This is a reduced version of a function posted on
[http://www.haskell.org/pipermail/haskell-cafe/2011-August/094434.html
Haskell Cafe]:
{{{
{-# LANGUAGE Arrows #-}
testB :: not_bool -> (() -> ()) -> () -> not_unit
testB b f = proc () -> if b then f -< () else f -< ()
}}}
There are two problems with the type of this function
* the first argument can be anything but should be {{{Bool}}} and
* the result type can be anything but should be {{{()}}}.
Yet the function is accepted by GHC.
This function can be used to define a value of arbitrary type:
{{{
anythingYouWant :: anything
anythingYouWant = testB () (const ()) ()
}}}
Here are some example calls from my machine:
{{{
ghci> anythingYouWant :: Int
1098066529
ghci> anythingYouWant :: String
""
ghci> anythingYouWant :: Char
'\1098066529'
ghci> anythingYouWant () :: ()
()
ghci> anythingYouWant () :: [()]
[()Segmentation fault
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5380>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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