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prologsubstring

All substring with 'a' character at the end

I received a task to write a Prolog program which can list all of those 'substrings' of a 'string', whose end with an 'a' character and length is at least two character.

For example:

?- avegu("baka", R).
R = "ba";
R = "baka";
R = "aka";
R = "ka";
false.

My idea is that I should split the given character list (string) to [Head|Tail] and call it recursively. When Head is 'a', returns the substring which I iterated over, then continue this until the end of the list. I don't know how to implement this idea.

Solution

  • If I use atoms and not strings then I can use atom_length/2 and sub_atom/5 but there are the same for "string" if you use SWI.

    babakaakaka(X, Sub) :-
    atom_length(X, Len),
    sub_atom(X, _, Sub_len, _, Sub),
    between(2, Len, Sub_len),
    sub_atom(Sub, _, 1, 0, a).

    and then I write:

    ?- babakaakaka(baka, X).
X = ba ;
X = baka ;
X = aka ;
X = ka ;
false.