PANIC in Type.Crush.Unify

[erikd]

This function is a variant of the solution to the Man or Boy Test.

a :: Int -> a -> a -> a -> a -> a -> Int
a k x1 x2 x3 x4 x5
 = do   b () = do { k := k - 1 ; nk = k ; a nk b x1 x2 x3 x4 }
        if k <= 0 then x4 () + x5 () else b ()

When trying to compile it, I get:

ddc: PANIC in Type.Crush.Unify
    errorConflict: Couldn't identify the error in class 202
       type: 
            Nothing
        
       queue: 
            [Base.Int32 %3, Base.Int32 %3 :- Base.Mutable %3]
        
       nodes:
            (tTC694_nk, TSV (SVInst ./Test.ds:5:44 nk))
            (Base.Int32 %3, TSV (SVInst ./Test.ds:5:44 nk))
            (@TFetter Class.Num.Num *174, TSV (SVInst ./Test.ds:5:27 (-)))
            (tTS2, TSV (SVInst ./Test.ds:5:27 (-)))
            (nk, TSU SU ./Test.ds:5:33)
            (tTC685_k, TSU SU ./Test.ds:5:33)
            (tTC683_k, TSV (SVInst ./Test.ds:5:25 k))
            (@TFetter Base.MutableT *156, TSV (SVInst ./Test.ds:5:20 (:=)))
            (@TFetter Class.Update.Updatable *156, TSV (SVInst ./Test.ds:5:20 (:=)))
            (tTS0, TSV (SVInst ./Test.ds:5:20 (:=)))
            (tTC679_k, TSV (SVInst ./Test.ds:5:20 k))
            (Base.Int32 %3, TSV SV ./Test.ds:2:2)
            (k, TSV SV ./Test.ds:3:0)

[erikd]

Test is in test/Broken-skip/T149-PanicTypeCrushUnify/

[benl]

Fixed by refactoring of type expressions.