Remove all substrings in a string

Help! Algorithm
7

Never underestimate append/3:

subst(This, That, MyStr, Result) :-
    append(This, After, Rest),
    append(Before, Rest, MyStr),
    !,
    subst(This, That, After, AfterResult),
    append([Before,That,AfterResult], Result).
subst(_, _, S, S).

To test:

103 ?- portray_text(true).
true.

104 ?- subst(`this`,`that`,`athishellothis`,R).
R = `athathellothat`.

But yes, especially if you have atoms or strings to begin with and portability is not a goal, re_replace/4 is probably a simpler and more efficient choice.

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