Re: [GHC] #8625: GHCi does not support some TH elements, while those elemenst are working in hs files

23 Dec 2013

      #8625: GHCi does not support some TH elements, while those elemenst are working in
hs files
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        Reporter:  danilo2           |            Owner:
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  GHCi              |          Version:  7.7
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by danilo2):

 We discovered now, that the error not always appears in GHCi session. It
 appears if we use following commands:

 :set -XTypeFamilies
 :set -XTemplateHaskell
 :set -XUndecidableInstances
 :set -XFlexibleInstances
 :set -XMultiParamTypeClasses
 :m + Language.Haskell.TH

 data Vector = Vector
 let test x = x
 class Member a f where member :: a -> f
 runQ [d| instance ( y ~ (t->t) ) => Member Vector y where member v = test
 |]

 <interactive>:19:6:
     Exotic predicate type not (yet) handled by Template Haskell
       y ~ (t -> t)

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8625#comment:1
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler