split(+Pattern, +String, +Options, -Parts)

Pattern

A string (or a compiled pattern handle)

String

A string

Options

List of atoms

Parts

Output: List of strings

Description

Options is a (possibly empty) list of atomic option names, as described in the library(regex) page.

Parts is bound to a list of strings which are consecutive substrings of the input string String (i.e. concatenating this list using concat_strings/2 will yield the original String). The list is constructed such that it has an odd number of elements, where the even numbered elements match the pattern, and the odd numbered elements contains those portions of String that did not match the Pattern. Some of these substrings may be empty.

This partitioning of the String can be used to construct a new string with the matches replaced by something else. Use the following code pattern:

	    split(Pattern, String, Options, Parts),
	    (
		fromto(Parts, [NoMatch,Match|NMs], NMs, [Last]),
		fromto(Repl,  [NoMatch,Subst|NSs], NSs, [Last])
	    do
		%%% compute Subst from Match here %%%
	    ),
	    concat_string(Repl, NewString),
	

Note that the split/4 predicate does not return any information about matching (parenthesised) sub-expressions!

Modes and Determinism

• split(+, +, +, -) is det

Fail Conditions

Examples

    ?- split("cad", "abracadabra", [], Parts).
    Parts = ["abra", "cad", "abra"]
    Yes (0.00s cpu)

    ?- split("bra", "abracadabra", [], Parts).
    Parts = ["a", "bra", "cada", "bra", ""]
    Yes (0.00s cpu)

    ?- split("bla", "abracadabra", [], Parts).
    Parts = ["abracadabra"]
    Yes (0.00s cpu)

    ?- split("a", "aaa", [], Parts).
    Parts = ["", "a", "", "a", "", "a", ""]
    Yes (0.00s cpu)
 
    ?- split("%[a-z]", "format %s %f=%d.", [], Parts).
    Parts = ["format ", "%s", " ", "%f", "=", "%d", "."]
    Yes (0.00s cpu)


    % With the following definition
    replace(Pattern, New, String, NewString) :-
	split(Pattern, String, [], Parts),
	(
	    fromto(Parts, [NoMatch,_Match|NMs], NMs, [Last]),
	    fromto(Repl,  [NoMatch, Subst|NSs], NSs, [Last]),
	    param(New)
	do
	    Subst = New
	),
	concat_string(Repl, NewString).

    ?- replace("2", "to", "2 be or not 2 be", S).
    S = "to be or not to be"
    Yes (0.00s cpu)
    

See Also