[GHC] #10764: GHC panic (no skolem info)

11 Aug 2015


      #10764: GHC panic (no skolem info)
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              Reporter:  zardoz      |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.10.2
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
             Test Case:              |        Blocked By:
              Blocking:              |   Related Tickets:
Differential Revisions:              |
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 The attached program causes GHC 7.10.2 to panic with the following output:

 bug.hs:6:19:
     Found hole ‘_’ with type: t1 → t2 → m1 a1 → m1 a1
     Where: ‘t1’ is a rigid type variable bound by
                 the inferred type of
                 whenMultipleOf ∷ MonadPlus m1 ⇒ t1 → t2 → m1 a1 → m1 a1
                 at bug.hs:7:1
            ‘a1’ is a rigid type variable bound by
                 the inferred type of
                 whenMultipleOf ∷ MonadPlus m1 ⇒ t1 → t2 → m1 a1 → m1 a1
                 at bug.hs:7:1
            ‘m1’ is a rigid type variable bound by
                 the inferred type of
                 whenMultipleOf ∷ MonadPlus m1 ⇒ t1 → t2 → m1 a1 → m1 a1
                 at bug.hs:7:1
            ‘t2’ is a rigid type variable bound by
                 the inferred type of
                 whenMultipleOf ∷ MonadPlus m1 ⇒ t1 → t2 → m1 a1 → m1 a1
                 at bug.hs:7:1
     To use the inferred type, enable PartialTypeSignatures
     In the type signature for ‘whenMultipleOf’: _

 bug.hs:7:1:
     No instance for (MonadPlus m)
     When checking that ‘whenMultipleOf’ has the specified type
       whenMultipleOf ∷ ∀ t a (m ∷ * → *) t1. t → t1 → m a → m a
     Probable cause: the inferred type is ambiguous

 bug.hs:10:62:
     Couldn't match type ‘a1’ with ‘t’
       ‘a1’ is a rigid type variable bound by
            the type signature for
              sumOfMultiples ∷ Integral a1 ⇒ [a1] → a1 → [a1]
            at bug.hs:9:19ghci-ng: panic! (the 'impossible' happened)
   (GHC version 7.10.2 for x86_64-unknown-linux):
         No skolem info: t_a7vV[sk]

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10764
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