## Type mismatch in local definitions in Haskell 98 code

Here is the affected code with all package dependencies removes:

```
$ cat PairMismatch.hs
module PairMismatch (inverseFrequencyModulationChunk) where
newtype VectorLazy a = VectorLazy a
newtype Vector a = Vector a
newtype Pointer a = Pointer a
empty :: VectorLazy a
empty = undefined
cons :: Vector a -> Pointer a
cons = undefined
unfoldrResult :: (a -> Either c (b, a)) -> a -> (VectorLazy b, c)
unfoldrResult = undefined
switchL :: b -> (a -> Pointer a -> b) -> Pointer a -> b
switchL = undefined
inverseFrequencyModulationChunk ::
(Num t, Ord t) =>
(s -> Maybe (t,s)) -> (t,s) -> Vector v -> (VectorLazy v, Maybe (t,s))
inverseFrequencyModulationChunk nextC (phase,cst0) chunk =
let {-
switch ::
(Maybe (t, s) -> r) ->
((t, v) -> (s, Pointer v) -> r) ->
t ->
(s, Pointer v) -> r
-}
switch l r t (cp0,xp0) =
maybe
(l Nothing)
(\(c1,cp1) ->
switchL
(l (Just (t,cp0)))
(\x1 xp1 -> r (t+c1,x1) (cp1,xp1))
xp0)
(nextC cp0)
{-
go ::
(t,v) -> (s, Pointer v) ->
Either (Maybe (t,s)) (v, ((t,v), (s, Pointer v)))
-}
go (c,x) cxp =
if c<1
then switch Left go c cxp
else Right (x, ((c-1,x),cxp))
in switch ((,) empty)
(curry $ unfoldrResult (uncurry go))
phase (cst0, cons chunk)
$ ghci-8.0.0.20160109 PairMismatch.hs
GHCi, version 8.0.0.20160109: http://www.haskell.org/ghc/ :? for help
[1 of 1] Compiling PairMismatch ( PairMismatch.hs, interpreted )
PairMismatch.hs:35:24: error:
• Couldn't match type ‘a’ with ‘(t, s)’
‘a’ is a rigid type variable bound by
a type expected by the context:
forall a. Maybe a
at PairMismatch.hs:35:24
Expected type: forall a. Maybe a
Actual type: Maybe (t, s)
• In the first argument of ‘l’, namely ‘(Just (t, cp0))’
In the first argument of ‘switchL’, namely ‘(l (Just (t, cp0)))’
In the expression:
switchL
(l (Just (t, cp0))) (\ x1 xp1 -> r (t + c1, x1) (cp1, xp1)) xp0
• Relevant bindings include
cp1 :: s (bound at PairMismatch.hs:33:20)
c1 :: t (bound at PairMismatch.hs:33:17)
cp0 :: s (bound at PairMismatch.hs:30:22)
t :: t (bound at PairMismatch.hs:30:19)
r :: (t, t1) -> (s, Pointer t1) -> b
(bound at PairMismatch.hs:30:17)
switch :: ((forall a. Maybe a) -> b)
-> ((t, t1) -> (s, Pointer t1) -> b) -> t -> (s, Pointer t1) -> b
(bound at PairMismatch.hs:30:8)
inverseFrequencyModulationChunk :: (s -> Maybe (t, s))
-> (t, s) -> Vector v -> (VectorLazy v, Maybe (t, s))
(bound at PairMismatch.hs:22:1)
(Some bindings suppressed; use -fmax-relevant-binds=N or -fno-max-relevant-binds)
Failed, modules loaded: none.
```

It works with GHC-7.10.3 and before. I may try to further simplify the code and choose a better ticket header, if I got an idea what went wrong.

## Trac metadata

Trac field | Value |
---|---|

Version | 8.0.1-rc1 |

Type | Bug |

TypeOfFailure | OtherFailure |

Priority | normal |

Resolution | Unresolved |

Component | Compiler (Type checker) |

Test case | |

Differential revisions | |

BlockedBy | |

Related | |

Blocking | |

CC | |

Operating system | |

Architecture |

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