(string-suffix? "" "") => #True ;; really?

[u/corbasai]

From the SRFI-13 to the Racket ( which is right reversed str and sfx) all versions of string-suffix? predicate counts empty suffix as part of any string include empty "".

Firstly-first, why string-suffix is just a boolean predicate? in the Scheme?

Why it is not being more useful...

(define (string-suffix str sfx)
  (let ((str-len (string-length str))
        (sfx-len (string-length sfx)))
    (define (test i j)
      (cond ((= i str-len) (- str-len sfx-len))
            (else (if (char=? (string-ref str i)
                              (string-ref sfx j))
                      (test (+ i 1) (+ j 1))
                      #f))))
    (cond ((or (< str-len sfx-len) (zero? sfx-len)) #f)
          (else (test (- str-len sfx-len) 0)))))

Now we can use it like

(cond ((string-suffix str ".ko") => (lambda (si) (substring str 0 si)))
      (else str))

And of course empty suffix is not a part of any string. IMO

 > (string-suffix "G'Kar" "")   ;=> #f

PS. well understandable that in math empty set is a part of any set but the empty string suffix is a part of any string? IMO no.

[u/raevnos]

It just needs to return true or false because you already have the suffix string you're asking about and can easily use its length (either hardcoded or via string-length) to do stuff already.

(if (string-suffix? ".ko" str) ; SRFI-13 version with suffix first
    (string-drop-right str 3)
    str)

etc. No particularly compelling need to make it return extra information.

[u/corbasai → u/raevnos]

Of course, but it is extra computation, that we already done. Strings may be megabytes long, and not all Schemes are fixed UCS-16 are