#7066: isInstance does not work for compound types
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Reporter: edsko | Owner: simonpj
Type: bug | Status: new
Priority: normal | Milestone:
Component: Template Haskell | Version: 7.4.2
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: None/Unknown
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Comment(by edsko):
Oh, I'm sorry. I would expect
{{{
isInstance clss typs
}}}
to return True if and only if I can safely generate code (in my Template
Haskell code) that relies on 'typs' being an instance of 'clss'. In the
example above, I can ''not'' safely generate code that relies on a Show
instance for (Int, A) because there is no Show instance for A. However, I
''can'' safely generate code that relies on a Show instance for (Int,
Bool), say.
Context: In Cloud Haskell when you call 'remotable' on a monomorphic
function f :: T1 -> T2, I automatically generate a top-level definition
{{{
f__sdict :: Static (SerializableDict T1)
}}}
but if T1 is not in fact serializable then this will subsequently cause a
type error. So I would like to check (using isInstance) if T1 is an
instance of Serializable before generating this code.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7066#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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