guile-examples/web-development/example-03-serve-static-assets/string-utils.scm

(define-module (string-utils)
  #:export (char->string
            string->char
            has-prefix?))


(use-modules
 (ice-9 exceptions))


(define char->string
  (λ (c)
    (list->string
     (list c))))


(define string->char
  (λ (str)
    "Convert a string, which has only one single character
into a character. This is useful, because some functions
expect a characters as input instead of a string."
    (cond
     [(= (string-length str) 1)
      (car (string->list str))]
     [else
      (raise-exception
       (make-exception
        (make-non-continuable-error)
        (make-exception-with-message "trying to convert string of more than 1 character to char")
        (make-exception-with-irritants (list str))
        (make-exception-with-origin 'string->char)))])))


(define has-prefix?
  (λ (str prefix)
    (= (string-prefix-length str prefix)
       (string-length prefix))))