[mercury-users] syntax across languages
Ralph Becket
rafe at cs.mu.OZ.AU
Mon Jun 3 10:19:36 AEST 2002
Pixel, Sunday, 2 June 2002:
> Fergus Henderson <fjh at cs.mu.oz.au> writes:
> > Multiple selection: two different syntaxes.
> >
> > (2) disjunctions:
> >
> > ( X = positive, ...
> > ; X = negative, ...
> > ; X = zero, ...
> > )
>
> one thing i try to have for the "switch" entry, is that the val only
> appears once (syntactically).
It seems a small thing to worry about. The Mercury term for a
disjunction where each arm is headed by a unification of a variable with
a different data constructor is `switch', precisely because of its
similarity to the C construct of the same name.
> this would be better in if_then_else where i give the n-ary
> if_then_else. The problem is I don't know if it would better with a
> comment telling the conditions must be separate, or writing explictly
> the cut
A Mercury switch is not the same as an if-then-else chain. For a start,
behaviour depends on the mode. Also (unless the right compiler flags are
given) the compiler is free to reorder the disjuncts.
> > (1) multiple clauses:
> >
> > foo(positive) = ...
> > foo(negative) = ...
> > foo(zero) = ...
>
> i'd prefer an anonymous solution. is there one?
This is it! The variable being switched on isn't even mentioned, so in
that sense it's even more `anonymous' than the C version.
- Ralph
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