CONST lzw_data$ = "TOBEORNOTTOBEORTOBEORNOT"

PRINT "LZWData: ", lzw_data$
encoded$ = Encode_LZW$(lzw_data$)
PRINT "Encoded: ", encoded$
PRINT "Decoded: ", Decode_LZW$(encoded$)

'----------------------------------------------------------

FUNCTION Encode_LZW$(sample$)

    LOCAL dict ASSOC int
    LOCAL ch$, buf$, result$
    LOCAL nr, x

    FOR nr = 0 TO 255
        dict(CHR$(nr)) = nr
    NEXT

    FOR x = 1 TO LEN(sample$)

        ch$ = MID$(sample$, x, 1)

        IF dict(buf$ & ch$) THEN
            buf$ = buf$ & ch$
        ELSE
            result$ = APPEND$(result$, 0, STR$(dict(buf$)))
            dict(buf$ & ch$) = nr
            INCR nr
            buf$ = ch$
        END IF
    NEXT

    result$ = APPEND$(result$, 0, STR$(dict(buf$)))

    RETURN result$

END FUNCTION

'----------------------------------------------------------

FUNCTION Decode_LZW$(sample$)

    LOCAL list$ ASSOC STRING
    LOCAL old$, ch$, x$, out$, result$
    LOCAL nr

    FOR nr = 0 TO 255
        list$(STR$(nr)) = CHR$(nr)
    NEXT

    old$ = TOKEN$(sample$, 1)

    ch$ = list$(old$)
    result$ = ch$

    FOR x$ IN LAST$(sample$, 1)

        IF NOT(LEN(list$(x$))) THEN
            out$ = list$(old$)
            out$ = out$ & ch$
        ELSE
            out$ = list$(x$)
        END IF

        result$ = result$ & out$
        ch$ = LEFT$(out$, 1)
        list$(STR$(nr)) = list$(old$) & ch$

        INCR nr
        old$ = x$
    NEXT

    RETURN result$

END FUNCTION