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Asked: 2026-06-15T17:42:15+00:00

Premise So I’m trying to break up a given String into a list of

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Premise

So I’m trying to break up a given String into a list of characters, these characters will then be edited/changed and reassigned into the list after which the list will be reconstructed back into a String.

An example:

Given String : "ABCDEFG"

Character list : [A,B,C,D,E,F,G]

Operation changes the list to something like the following:
[E,F,G,H,I,J,K] (Or something similar).

And then gets reconstructed into a String:

"EFGHIJK"

Question

I am looking for a way to access individual elements inside of a String. If it were Java I would use a command like charAt(int i) but I don’t know if such a command exists within prolog.

Note

I am a new prolog programmer so I’m not familiar with most prolog operations.

Thanks for your time.

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1 Answer

  1. Editorial Team

    A string it’s a list of char codes, while an atom it’s, well, atomic, i.e. indivisible, but there is sub_atom/5 to access parts of the atomic data.

    Here some string example:

    1 ?- L = "ABCDEF".
L = [65, 66, 67, 68, 69, 70].

2 ?- L = "ABCDEF", maplist(succ, L, N), format('~s', [N]).
BCDEFG
L = [65, 66, 67, 68, 69, 70],
N = [66, 67, 68, 69, 70, 71].

3 ?- L = "ABCDEF", maplist(succ, L, N), format('~s', [N]), atom_codes(A, N).
BCDEFG
L = [65, 66, 67, 68, 69, 70],
N = [66, 67, 68, 69, 70, 71],
A = 'BCDEFG'.

    If the analysis and transformation require detail then usually it’s better to use DCGs

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