[m-dev.] Replacing pairs with 2-tuples

[Ralph Becket]

I was wondering whether it might be wise to consider migrating from
the pair type to 2-tuples by changing to...

:- type pair(T1, T2) == {T1, T2}.

:- func T1 - T2 = pair(T1, T2).
:- mode in - in = out is det.
:- mode out - out = in is det.
X - Y = {X, Y}.

:- func fst(pair(T1, T2)) = T1.
fst(Pair) = X :-
	X - _ = Pair.

:- func snd(pair(T1, T2)) = T2.
snd(Pair) = Y :-
	_ - Y = Pair.

We could mark -/2 as being deprecated and eventually do away with it
altogether.

The motivation for doing this is
(a) to avoid having two pairing types and
(b) to reduce pollution of the name-space and
(c) to steal back fst/1 and snd/1 for 2-tuples.

Objections?  Problems?

--
Ralph Becket      |      MSR Cambridge      |      rbeck at microsoft.com 
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