parsingprologdcgmeta-predicate

How to create a higher order DCG parser in Prolog?

I would like to have some more general parsers, like for example paren that would take a parser and wrap it with parentheses:

paren(Parser, Result) -->
  "(", some_magic_dcg_call(Parser, Result), ")".


:- phrase(paren(number, N), "(123)").
123
:- phrase(paren(someatom, A), "(a)").
a

I tried call and dcg_call, but they don't seem to solve the problem. How can I run an arbitrary parser inside another parser?

Solution

  • This solution using call works in SWI-Prolog:

    :- set_prolog_flag(double_quotes, chars).

paren(Parser, Result) -->
    "(",
    call(Parser, Result),
    ")".

number(123) -->
    "123".

someatom(a) -->
    "a".

    Tests: 

    ?- phrase(paren(number, N), "(123)").
N = 123.

?- phrase(paren(someatom, A), "(a)").
A = a.