#6065: Suggested type signature causes a type error (even though it appears
correct)
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Reporter: tvynr | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler (Type
checker)
Version: 7.4.1 | Keywords: type signature
typeclass instance forall
Os: Linux | Architecture: x86_64 (amd64)
Failure: GHC rejects valid program | Testcase:
Blockedby: | Blocking:
Related: |
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The attached file, MWE.hs, contains an experiment attempting a rudimentary
encoding of extensible ASTs in Haskell (without using compdata or a
similar package relying upon OverlappingInstances and so forth). The
definition of the upcast function appears to be correct. Compiling
without a type signature produces a warning and the suggestion to include
a type signature. Including the suggested type signature (which appears
to be the correct one) causes a type error.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6065>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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