Re: "maplist" for DCG?

Hi Edison,

Logtalk provides a meta_non_terminal/1 directive that is handy for these cases:

On 23/11/2013, at 16:36, Edison Mera <[email protected]> wrote:

> Once ago I have a similar need, and implemented a set of maplist_dcg//N
> predicates in one of my libraries, basically is the code Richard wrote for
> mapnt, but using the call/(N+1) predicates:
> 
> :- module(maplist_dcg, [maplist_dcg/4,
>                        maplist_dcg/5,
>                        maplist_dcg/6,
>                        maplist_dcg/7,
>                        maplist_dcg/8,
>                        maplist_dcg/9]).

I'm under the impression that SWI-Prolog also supports the notation:

:- module(maplist_dcg, [
    maplist_dcg//2,
    maplist_dcg//3,
    ...
]).

> :- meta_predicate maplist_dcg(3, ?, ?, ?).

:- meta_non_terminal(maplist_dcg(1, ?)).

> maplist_dcg(Goal, List) -->
>    maplist_dcg_(List, Goal).
> 
> :- meta_predicate maplist_dcg_(?, 3, ?, ?).

:- meta_non_terminal(maplist_dcg_(?, 1)).

> maplist_dcg_([],    _) --> [].
> maplist_dcg_([E|T], Goal) -->
>    call(Goal, E),
>    maplist_dcg_(T, Goal).
> 
> :- meta_predicate maplist_dcg(4, ?, ?, ?, ?).

...

The directive is easy to implement and, in the same way as NonTerminal//Arity, it allows to abstract the implicit arguments.

Cheers,

Paulo

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Paulo Moura
Logtalk developer

Email: <mailto:[email protected]>
Web:   <http://logtalk.org/>
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