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Related to #255 (closed). Given (roughly) the example from that ticket:

f :: (Storable a, Eq a) => T a

g :: T (Ptr a)
g = f

we find that g is not specialised. Adding a SPECIALISE pragma fixes this, but it ought not to be necessary.

The following module is a complete example:

module C where

class C a where f :: a -> a

newtype Id a = Id a
instance C (Id a) where f = id

g :: C a => Int -> a -> a
g 0 a = a
g n a = g (n-1) (f a)

h :: Int -> Id a -> Id a
h = g

j :: Int -> Id Int -> Id Int
j = g

We find that h passes a dictionary to g:

C.h =
  \ (@ a_alq) (w_smq :: Int) (w1_smu :: C.Id a_alq) ->
    case w_smq of _ { I# ww_sms ->
    C.$wg @ (C.Id a_alq) (C.$fCId @ a_alq) ww_sms w1_smu
    }

whereas j is specialised as desired, getting its own worker and no dictionaries:

C.j =
  \ (w_smg :: Int) (w1_smk :: C.Id Int) ->
    case w_smg of _ { I# ww_smi ->
    (C.$wj ww_smi w1_smk)
    `cast` (sym (C.NTCo:Id Int)
            :: Int ~ C.Id Int)
    }

If we add

{-# SPECIALISE g :: Int -> Id a -> Id a #-}

then h is specialised as desired.

Trac metadata

Trac field	Value
Version	7.0.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture