SWI-Prolog -- sub

Availability:built-in

sub_string(+String, ?Before, ?Length, ?After, ?SubString)

This predicate is functionally equivalent to sub_atom/5, but operates on strings. Note that this implies the string input arguments can be either strings or atoms. If SubString is unbound (output) it is unified with a string. The following example splits a string of the form <name>=<value> into the name part (an atom) and the value (a string).

name_value(String, Name, Value) :-
    sub_string(String, Before, _, After, "="),
    !,
    sub_atom(String, 0, Before, _, Name),
    sub_string(String, _, After, 0, Value).

The next example defines a predicate that inserts a value at a position. See sub_atom/5 for more examples.

string_insert(Str, Val, At, NewStr) :-
    sub_string(Str, 0, At, A1, S1),
    sub_string(Str, At, A1, _, S2),
    atomics_to_string([S1,Val,S2], NewStr).