[mercury-users] A subtlety about DCG variable threading

Ralph Becket rbeck at microsoft.com
Thu Apr 26 20:38:41 AEST 2001


> It was my understanding that the only terms in a clause which would
> not receive DCG threading were those that were escaped with { }.

That is correct: DCG expansion is purely syntactic.

> My guess is that the process/3's modes are not compatible with those
> of the head of the DCG (specifically, they are not di and uo) and that
> somehow Mercury selectively engages in the biblical act of Passover on
> them because of this, the bloody mark on the door in this case being
> incompatible modes.

No.  Can you tell us what sort of error message you're getting?  Seeing
the signature of process/5 might allow us to offer better help.
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