[mercury-users] Determinism of if-then-elses

[Nicholas Nethercote]

On Wed, 12 Apr 2006, Mark Brown wrote:

>> So why does the following code from library/lexer.m compile?  The line
>> marked XXX seems to be doing exactly what causes problems in my code.
>
> That goal has no output variables.  In such a case all "solutions" must
> be equivalent, so the compiler (safely) prunes away any solutions after
> the first.  This changes the nondet goal into a semidet one.
>
> In your case, I guess either S or one of the DCG arguments is an output,
> so the pruning cannot happen.

Ah, I see.  Thanks.

Nick
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