Confusing behavior of sequence//3 and sequence//5 from dcg/high_order

Help!
15

Now that I had to try and motivate my choices, I changed my mind. Greedy parsing is probably more useful if we do not generate a list, by default. Maybe the functionality in my half-baked module detparse is meant to be used with library(intercept). You can still collect all elements to a list using intercept_all/4 and nb_intercept_all/4.

$ cat greedyparse.pl 
:- module(greedyparse, [greedy_sequence//1,
                        greedy_sequence//2,
                        greedy_sequence//4]).
:- meta_predicate greedy_sequence(3, ?, ?).
:- meta_predicate greedy_sequence(3, //, ?, ?).
:- meta_predicate greedy_sequence(//, 3, //, //, ?, ?).

:- use_module(library(intercept)).

greedy_sequence(Goal) -->
    call(Goal, X),
    { send_signal(X) },
    !,
    greedy_sequence(Goal).
greedy_sequence(_) --> [].

greedy_sequence(Goal, Sep) -->
    call(Goal, X),
    { send_signal(X) },
    greedy_sequence_1(Goal, Sep).

greedy_sequence_1(Goal, Sep) -->
    Sep,
    call(Goal, X),
    { send_signal(X) },
    !,
    greedy_sequence_1(Goal, Sep).
greedy_sequence_1(_, _) --> [].

greedy_sequence(Start, Goal, Sep, End) -->
    Start,
    greedy_sequence(Goal, Sep),
    End.

With this, I can still make a list if I wanted to:

?- intercept_all(N, phrase(greedy_sequence("|", integer, "|", "|"), `|1|2|3|`), N, L).
L = [1, 2, 3].

… but I can also parse a large file in constant memory, intercepting only those elements that are interesting to me.

@jan Do you think there is any merit to doing this? How about adding those predicates to a library? Where should they go and what should they be called and so on? Are they useful and is the interface good?