(library (ikarus strings)
  (export string-ref)
  (import 
    (except (ikarus) string-ref)
    (only (scheme) $string-ref $fx<= $fx< $string-length))
  (define (string-ref s i)
    (unless (string? s) 
      (error 'string-ref "~s is not a string" s))
    (unless (fixnum? i)
      (error 'string-ref "~s is not a valid index" i))
    (unless (and ($fx< i ($string-length s))
                 ($fx<= 0 i))
      (error 'string-ref "index ~s is out of range for ~s" i s))
    ($string-ref s i)))