Question

I’m just starting with Scheme.

I’m trying to use some procedures from String Library.

Here’s what I need:

input: “ccaAaAaAa”

function: generate all strings substituting all possible aAa to aBa, one substitution only

output: “ccaBaAaAa” and “ccaAaBaAa” and “ccaAaAaBa”

Is there any easy way to do that? Maybe a procedure that return a list of index of pattern found?

Apparently the searching function string-contains only returns the first occurrence.

What I thought is: after producing the first string “ccaBaAaAa”, trim to the first index of the pattern found: the original “ccaAaAaAa” becomes “AaAaAa”. Repeat (recursively).

Thanks.

Answer 1

I thought there could be better string libraries that I didn’t know about. But I end up doing what I’d proposed in the question. (For a general input case)

(define (aplicarRegra cadeia cadeiaOriginal regra n)
  (let* ((antes (car regra))
         (depois (cdr regra))
         (index (string-contains cadeia antes))
         (tamanho (string-length antes))
         (diferenca (- (string-length cadeiaOriginal) (string-length cadeia))))

    (if index
       (let* ((cadeiaGerada (string-replace cadeiaOriginal depois (+ index diferenca) (+ index diferenca tamanho))))

          (if(<= (string-length cadeiaGerada) n)
             (lset-union equal? (list cadeiaGerada) (aplicarRegra(substring cadeia (+ 1 index)) cadeiaOriginal regra n))
             (aplicarRegra (substring cadeia (+ 1 index)) cadeiaOriginal regra n)))
       (list))))

But thanks anyway!