🚀 go-pugleaf

In article <MATSC.89Dec8125828@vishnu.sics.se> matsc@sics.se (Mats Carlsson) writes:
> prefix operators
>with precedence > 999 must be parenthesized *in the canonical syntax*
>when they occur in compound terms, as in
>
>	p((public)).

In the NU-Prolog parser parentheses are not needed in this context,
which is certainly an advantage for canonical IO.  Unfortunately, some
input which "standard" parsers can handle is not accepted by NU-Prolog.
The main reason for the nonstandard parser is so we can have prefix
binary operators (for quantifiers).

>The canonical syntax would become independent of op declarations if
>the two (**) rules and the constraint on @var{atom} not being a prefix
>operator were deleted.  Would this measure make it more difficult to
>parse or cause any other bad effects?

Not being an expert in parsing (or Prolog syntax) I don't know
what bad effects there might be (possible ambiguity?).  However, the
grammar modifications suggested by Mats don't correspond to what
NU-Prolog is able to parse.  "not ?- ." causes an error, for example,
even though it is unambiguous.  By adopting Mats' scheme more
unambiguous, currently unparsable terms could be parsed.

	lee