Re: more version 7 woes re phrase/3

Hi Samer,

"Abdallah, Samer" <[email protected]> writes:

> I often use DCG notation to write all sorts of stateful code where the
> threaded value is not a list, but, e.g. a pair (X,Y) or a number. Is
> there any work around for this restriction?

Consider using a single-element list that contains the term you want to
pass around. This introduces only a very small overhead, keeps your DCG
completely portable and still exclusively describes lists. For example:

   phrase(nt, [(X,Y)], [Result])

You can use call//1 from within DCGs to pass the implicit arguments to
regular Prolog predicates in a portable way that does not rely on any
particular DCG expansion method and is backwards-compatible with the
traditional expansion method which is also used in SWI.

Useful nonterminals for accessing the state with semicontext notation:

   state(S), [S] --> [S].

   state(S0, S), [S] --> [S0].

state(S) in a DCG body can be read as: "The current state is S".

state(S0, S) can be read as: "The current state is S0, and henceforth it
is S".

All the best,
Markus