Highlist by Alberto Apostolo

H I G H L I S T : HAVING A LIST WITH COLORFUL SPECCY TOKENS!
          ===========================================================
(By Alberto Apostolo 2021/02/05)

1. Getting Started
------------------

This utility for ZX Spectrum (coded without "GO TO"s) lists a program showing
 colorful BASIC tokens.
It could be appended to another BASIC program in order to have a colorful list,
 running the command "RUN 9000" or "GO TO 9000".
At line 9010, you can set different values to the variables "ls" (line-start)
 and "le" (line-end) in order to list just few lines and not an entire program. 
Because it's coded without "GO TO"s, it also possible renumber this utility
 as you like.

2. Program Structure
--------------------

Line  9000     : Remarks

Line  9010     : Initialization of variables ls (line-start), le (line-end).
                 Calculation of s (program start address)  and e 
                                  (program end address/variables start address)
                 pointed by Spectrum system variables PROG (addr. LSB-MSB 23635/6)
                 and VARS (addr. LSB-MSB 23627/8).
                 Set foreground and background default colors.
                 Begin main n-loop.

Line  9020     : Initialization of a$, needed to store a line of BASIC program.
                 Each line of BASIC program has the form:
                    - Line number                : 2 bytes (HSB,LSB)
                    - Length text included ENTER : 2 bytes (LSB,HSB)
                    - Text                       : 1 or more bytes
                    - ENTER                      : 1 byte.
                 Calculation of q (line number) and w (length text).
                 Increase of n by 3.

Line  9030     : If q greater than ls then "break;" the n-loop (by means of that "weird" FOR)
                 (the limit value has been exceeded)

Line  9040     : If q greater or equal ls then initialize a$ with q (converted in
                 string and justified right when q < 1000).

Line  9050     : Begin "Parsing Text" m-loop (performed if a$ is not empty).
                 Store in z the content of memory cell addressed by n+m.
                 Choose a color for the BASIC token (black for other characters):
                    - Magenta for functions (coded from 165 to 194)
                    - Red     for binary operators (coded from 195 to 201)
                    - Blue    for commands (coded from 202 to 255)
                    - Green   for REM (coded 234).

Lines 9060-9070: Deploy of a kind of "CASE-WHEN" ("weird" FOR even here):
                     CASE WHEN z>164 THEN add a colored BASIC token (coded z) to a$
                                     (chr 16 represents INK control, chr in variabile c 
                                                                     represents a color,
                                      chr 0  represents black, the foreground default color)
                          WHEN z=14  THEN skip next 5 bytes after a numeric literal 
                                     ( chr 14 is a delimiter)
                          WHEN z=13  then print a$ on screen
                          ELSE add the character (coded z) to a$
                      END-CASE.
                 End of m-loop.   
                                  
Line  9080     : Increase of n by w (length of text).
                 End of main n-loop.
                 Restore background and foreground default colors.
                 End of utility.

3. Listing
----------

9000 REM HIGHLIST (apoalb 2021)
9010 LET ls=1: LET le=9999: LET s=23635: LET s=256*PEEK (s+1)+PEEK s: LET e=23627:
     LET e=256*PEEK (e+1)+PEEK e: CLS: INK 0: PAPER 7: FOR n=s TO e-1
9020 LET a$="": LET q=PEEK (n+1)+256*PEEK n: LET w=256*PEEK (n+3)+PEEK (n+2):n=n+3
9030 IF q>le THEN FOR n=1 TO 0
9040 IF q>=ls THEN LET a$=STR$ q: LET a$="   "( TO 4-LEN a$)+a$
9050 FOR m=1 TO w*(a$<>""): LET z=PEEK (n+m): LET c=3*(z>=165 AND z<=194) +2*(z>=
     195 AND z<=201)+(z>=202): LET c=c+3*(z=234)
9060 LET k=3*(z>164)+2*(z=14)+(z=13): FOR g=1 TO K=3: LET a$=a$+CHR$ (16)+ CHR$(c)
     +CHR$ (z) +CHR$ (16)+ CHR$(0): NEXT g: FOR g=1 TO k=2: LET m=m+5: NEXT g
9070 FOR g=1 TO k=1: PRINT a$: NEXT g: FOR g=1 TO k=0: LET a$=a$+CHR$ (z): NEXT g:
     NEXT m
9080 LET n=n+w: NEXT n: PAPER 7: INK 0: STOP