string/1

Availability:built-in

string(@Term)

True if Term is bound to a string. Note that string here refers to the built-in atomic type string as described in section 5.2. Starting with version 7, the syntax for a string object is text between double quotes, such as "hello".^{65In
traditional Prolog systems, double quoted text is often mapped to a list
of character codes.} See also the Prolog flag double_quotes.

Examples

Convert a string of 0s and 1s to an integer

This shows how to convert almost any "string" of 0s and 1s to an integer.

It takes advantage of the built-in term reading, thus avoiding an explicit loop and arithmetic.

binary_string_to_int(Str, Int) :-
    (   ( string(Str) ; atom(Str) )
    ->  atomics_to_string(["0b", Str], Literal)
    ;   is_list(Str)
    ->  atomics_to_string(["0b"|Str], Literal)
    ;   type_error(string_type, Str)
    ),
    catch(term_string(Int, Literal, []),
          error(syntax_error(_), _),
          type_error(string_of_0s_and_1s, Str)).

?- binary_string_to_int('101', X).
X = 5.

?- binary_string_to_int([0, 0, 1, 0, 1], X).
X = 5.

?- binary_string_to_int(["1", "1", "0"], X).
X = 6.