## #189 closed bug (Fixed)

# Malformed Predicate w/ Template Haskell

Reported by: | jcast | Owned by: | nobody |
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Priority: | normal | Milestone: | |

Component: | Compiler (Type checker) | Version: | 6.0.1 |

Keywords: | Cc: | ||

Operating System: | Architecture: | ||

Type of failure: | None/Unknown | Test Case: | |

Blocked By: | Blocking: | ||

Related Tickets: | Differential Rev(s): | ||

Wiki Page: |

### Description

The following two modules: --- Cut --- module ScratchTemplates where import Language.Haskell.THSyntax newtype Interaction a = Interaction a deriving Show ret = Interaction instance Monad Interaction where return = Interaction Interaction x >>= f = f x instance Functor Interaction where fmap f x = x >>= return . f interactionT t = tcon (TconName "Interaction") `tapp` t class Flatten a b | a -> b where flatten :: a -> b flattenT :: TypQ -> TypQ -> TypQ flattenT t t' = tvar "Flatten" `tapp` t `tapp` t baseType t = sequence [ inst (return []) (flattenT t t) [val (pvar "flatten") (normal (var "id")) []], inst (return []) (flattenT (interactionT t) (interactionT t)) [val (pvar "flatten") (normal (var "id")) []]] instance Flatten a b => Flatten (Interaction (Interaction a)) (Interaction b) where flatten a = a >>= id >>= return . flatten module Main where import Monad import ScratchTemplates import Language.Haskell.THSyntax $(baseType (tcon (Tuple 0))) instance Flatten String String where flatten a = a instance Flatten (Interaction String) (Interaction String) where flatten a = a instance Flatten b c => Combine String b (String, c) where combine a b = liftM2 (,) a (fmap flatten b) instance Flatten Int Int where flatten a = a class Combine a b c | a b -> c where combine :: Interaction a -> Interaction b -> Interaction c instance Combine () b b where combine a b = b instance Flatten b c => Combine Int b (Int, c) where combine a b = do x <- a y <- fmap flatten b return (x, y) instance (Flatten b c, Combine a c d) => Flatten (Interaction a, Interaction b) (Interaction d) where flatten (a, b) = combine a (fmap flatten b) main = main --- Cut here --- loaded into ghci -fglasgow-exts produce the following error message: Compiling ScratchTemplates ( ScratchTemplates.hs, interpreted ) Compiling Main ( scratch.hs, interpreted ) ghc-6.0.1: panic! (the `impossible' happened, GHC version 6.0.1): Malformed predicate Please report it as a compiler bug to glasgow-haskell-bugs@haskell.org, or http://sourceforge.net/projects/ghc/.

### Change History (2)

### comment:2 Changed 13 years ago by

Status: | assigned → closed |
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Logged In: YES user_id=50165 Fixed in the HEAD

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