🚀 go-pugleaf

Andrew Butterfield writes:

>Can anyone explain the following aspect of the Miranda and Haskell type
>systems that I find annoying ? Is there a theoretical reason for it ?

>pairs, triples, quintuples, etc.. are _distinct_ types. In particular,
>(a,(b,c)) != ((a,b),c) != (a,b,c).

Fergus James HENDERSON replies:

>Theoretically I see no reason why (a,b,c) should be required to be
>equal to say (a,(b,c)). That seems like implementation details to me.
>It's also very assymetric - you have to require either left-pairing
>or right-pairing, and there is no obvious reason to prefer one over the
>other. It makes perfect sense to me that (a,b,c) is quite simply not a
>pair!

Of course, it is also impossible to let ((a,b),c) = (a,(b,c)), unless
you want to end up having a nondeterministic language. For if a
function expecting a pair were applied to such a thing, you would never
know whether to match its argument with ((a,b),c) or (a,(b,c)).

                                                               Vincent.