Probably buggy implementation of Lempel-Lev-Welch compression algorithm

compress.rkt

#lang racket

(define (compress uncompressed)
  (let ([table (for*/hash ([i (in-range 256)]
                           [str (in-value (string (integer->char i)))])
                 (values str i))]) 
    (for*/fold ([w ""]
                [size 256]
                [result null]
                [tbl table] #:result `(,result . ,table))
               ([c (in-string uncompressed)]
                [wc (in-value (begin (displayln "hey") (string-append w (string c))))]) 
      (if (hash-has-key? tbl wc)
          (values wc
                  size
                  result
                  tbl) 
          (values (string c)
                  (add1 size)
                  (hash-ref tbl w)
                  (hash-set tbl wc size))))))