[bitc-dev] Pairing convenience syntax

Jonathan S. Shapiro shap at eros-os.org
Thu Aug 25 18:37:33 EDT 2005


The latest specification has a provisional convenience syntax for pair
that is not yet implemented. I would appreciate input.

The specification currently says that

 	(a, b)  =>   (pair a b)
        (a, b, c) => (pair a (pair b c))

PAIR is a value type, so the above syntax can have some strange
repurcusions. In particular:

	(a, (b, c)) => (pair a (pair b c))

and therefore

	(a, b, c) unifies with (a, (b, c))

A possible alternative is to say that the syntax is

	a,b

that is: unparenthesized. I am inclined not to do this, because it
introduces some annoying operator precedence issues. Also, it would
create the following *alternative* anomaly:

	(a, b) => ((pair a b)) => ((pair a b) ())

which is application. Of the two, I think that the nested parenthesis
issue is the lesser surprise.

Can anyone articulate a compelling reason to choose "a,b" over "(a,b)"?

shap



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