split string on delimiter

[mvolkmann]

How can I split a string on a delimiter in Scryer Prolog?
In SWI-Prolog I use split_string, but it appears that does not exist in Scryer Prolog.

[triska]

In Scryer Prolog, you can easily reason about strings as lists, so the predicates from library(lists) or library(dcgs) may be useful to describe what you want.

For example:

:- use_module(library(lists)).
:- use_module(library(reif)).

split("", _, []).
split(String, Char, Segments0) :-
        if_(memberd_t(Char, String),
            (   Segments0 = [Segment|Segments],
                once(append(Segment, [Char|Rs], String)),
                split(Rs, Char, Segments)
            ),
            Segments0 = [String]
           ).

Yielding:

?- split("hello.all.there", ., Rs).
   Rs = ["hello","all","there"].

[triska]

Regarding correctness: Yes, special consideration may be needed for situations where the string begins or ends with Char! Please modify the predicate if necessary so that it fits your use case, and there may well be better ways to express this!

[mvolkmann]

My particular use case is that I pass a file name into a Prolog program and I want to get the name of the file without its extension. So if I pass in "foo.bar", I want to split on the period and get "foo". Maybe there's an easier way to do that then creating a split predicate.

[mvolkmann]

I didn't consider using DCGs as I'm pretty new to those. But this seems to work great!

split(Delimiter, Prefix, Suffix) --> seq(Prefix), Delimiter, seq(Suffix).
filename_extension(Filename, Extension) --> split(".", Filename, Extension).

[triska]

Maybe append/3?

?- append(Prefix, [.|Suffix], "foo.bar").
   Prefix = "foo", Suffix = "bar"
;  false.

[david-sitsky]

Just be aware of filenames like this: 2023.07.25.txt