#2597: panic! (the 'impossible' happened) (using TH)
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Reporter: jcab | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Template Haskell | Version: 6.8.3
Severity: major | Resolution:
Keywords: | Difficulty: Unknown
Testcase: | Architecture: x86
Os: Windows |
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Comment (by jcab):
A-ha! I've reduced this to the minimal. It is caused by trying to expand
list comprehensions:
mkBug = returnQ $ CompE [BindS (VarP $ mkName "p") (ListE []), NoBindS
(VarE $ mkName "p")]
That simple template causes the panic (on 6.8.3) when invoked:
bug = $mkBug
My code seems to work correctly if I get the comprehensions eliminated at
template-compile time so there are no comprehensions in the returned
expression tree.
BTW: defining comprehensions as "CompE [Stmt]" is... weird. Putting the
two statements in the opposite order doesn't change the outcome.
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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2597#comment:2>
GHC <http://www.haskell.org/ghc/>
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