>It sounds to me as if the problem is with negative numbers.
>So, one more time ... What about the *natural* numbers?
>Doesn't anyone else program with these? (Maybe just occasionally? :-)
The problem is only partly to do with naturals. Having these would
certainly improve matters but I suspect the Num class is big enough
already. However, some other problems of (n+k) patterns are
* syntax: + is the only nonconstructor constant allowed in patterns.
* generality: mathematics commonly uses (bn+k) patterns, but Haskell doesn't
allow this. It has one series of special cases only.
* construction: laws were thrown out of Miranda because of the confusion
created when something built one way, was taken apart another way. All our
patterns *except (n+k)* have the property that the deconstruction reverses
construction. If I build (a:as) then take it apart with pattern (x:xs) then
x is a, and xs is as. If I build (a+b) then take it apart with pattern
(n+1) then I cannot deduce that n is a (nor that 1 is b).
John.
