#7856: Wrong error message for unknown Instance
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Reporter: bas | Owner:
Type: feature request | Status: new
Priority: normal | Component: Compiler (Type
checker)
Version: 7.6.3 | Keywords: Instance
Os: Unknown/Multiple | Architecture:
Unknown/Multiple
Failure: Incorrect warning at compile-time | Blockedby:
Blocking: | Related:
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This type-incorrect program gives a wrong error message:
{{{
main = tmp "hello"
where tmp :: String -> IO ()
tmp = sequence_ lst
lst = [putStrLn "hi"]
}}}
Namely:
{{{
Couldn't match expected type `IO ()' with actual type `()'
Expected type: String -> IO ()
Actual type: String -> ()
In the return type of a call of `sequence_'
In the expression: sequence_ lst
}}}
I would not expect the "actual type" to be "String -> ()", but rather "IO
()". Note: GHC expects that "(->) String" is a monad.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7856>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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