This is to convert tokenized BBC BASIC for Windows files to a human-readable (plain text) format. Note that this will probably not handle tokenized files from other versions of BBC BASIC -- specifically, I know that the RISC OS version uses a different format (see this page and this page at the BB4W wiki).

Two pages that may be of interest at the BB4W wiki are Tokeniser and Detokeniser, both of which discuss this topic using BBC BASIC code.

I believe that the previous issues with line numbers as the targets of GOTO and the like has been fixed, using a QB translation of code on the above-mentioned Detokeniser page at the BB4W wiki. (View the page history for details, if you're interested.)

The VBA code that generates the below program has been moved to its own page.

Licensing

The GNU General Public License (GNU GPL) v2 or, at your option, any later version.
The GNU Free Documentation License (GNU FDL) v1.2 or, at your option, any later version.

The two licenses are not 100% compatible; which license you use, I leave up to you.

Exception

Any source code that is generated by the generated QBasic program (only) is specifically excluded from the above licensing terms, and is instead covered by whatever license(s) cover the original, tokenized sources.

Detoken.bas

This is the code that actually does the work. I chose QBasic for a number of reasons, the most important of which are:

interpreter (no compile time)
simple
ease of including in batch files

Note that since I expect the code to run under QBasic, you don't specify the file(s) to be detokenized on the command line, but instead do it one file at a time, via the DETOKEN environment variable. (This can easily be changed, but I don't care to.)

<lang qbasic>DATA 1,CIRCLE,2,ELLIPSE,3,FILLED,4,MOUSE,5,ORIGIN,6,QUIT,7,RECTANGLE,8,SWAP,9,SYS,10,TINT DATA 11,WAIT,12,INSTALL,14,PRIVATE,15,BY,16,EXIT,128,AND,129,DIV,130,EOR,131,MOD,132,OR DATA 133,ERROR,134,LINE,135,OFF,136,STEP,137,SPC,138,TAB(,139,ELSE,140,THEN,142,OPENIN,143,PTR DATA 144,PAGE,145,TIME,146,LOMEM,147,HIMEM,148,ABS,149,ACS,150,ADVAL,151,ASC,152,ASN,153,ATN DATA 154,BGET,155,COS,156,COUNT,157,DEG,158,ERL,159,ERR,160,EVAL,161,EXP,162,EXT,163,FALSE DATA 164,FN,165,GET,166,INKEY,167,INSTR(,168,INT,169,LEN,170,LN,171,LOG,172,NOT,173,OPENUP DATA 174,OPENOUT,175,PI,176,POINT,177,POS,178,RAD,179,RND,180,SGN,181,SIN,182,SQR,183,TAN DATA 184,TO,185,TRUE,186,USR,187,VAL,188,RND,189,CHR$,190,GET$,191,INKEY$,192,LEFT$,193,MID$( DATA 194,RIGHT$,195,STR$,196,STRING,197,EOF,198,SUM,199,WHILE,200,CASE,201,WHEN,202,OF,203,ENDCASE DATA 204,OTHERWISE,205,ENDIF,206,ENDWHILE,207,PTR,208,PAGE,209,TIME,210,LOMEM,211,HIMEM,212,SOUND,213,BPUT DATA 214,CALL,215,CHAIN,216,CLEAR,217,CLOSE,218,CLG,219,CLS,220,DATA,221,DEF,222,DIM,223,DRAW DATA 224,END,225,ENDPROC,226,ENVELOPE,227,FOR,228,GOSUB,229,GOTO,230,GCOL,231,IF,232,INPUT,233,LET DATA 234,LOCAL,235,MODE,236,MOVE,237,NEXT,238,ON,239,VDU,240,PLOT,241,PRINT,242,PROC,243,READ DATA 244,REM,245,REPEAT,246,REPORT,247,RESTORE,248,RETURN,249,RUN,250,STOP,251,COLOUR,252,TRACE,253,UNTIL DATA 254,WIDTH,255,OSCLI,0

DIM lineNum AS LONG, encoded AS STRING * 1 DIM tmp AS LONG, lineNumDec AS LONG DIM keywords(255) AS STRING DO

   READ t%
   IF 0 = t% THEN EXIT DO
   READ keywords(t%)

LOOP nm$ = ENVIRON$("DETOKEN") OPEN nm$ + ".bbc" FOR BINARY AS 2 OPEN nm$ + ".bas" FOR OUTPUT AS 3 'skip first char GET #2, , encoded GET #2, , lineNum SEEK #2, SEEK(2) - 2 lineNum = (lineNum AND &HFFFF&) IF (CHR$(0) = encoded) AND (&HFFFF& = lineNum) THEN

   CLOSE : SYSTEM

ELSEIF lineNum <> 0 THEN

   PRINT #3, LTRIM$(STR$(lineNum)); " ";

END IF DO UNTIL EOF(2)

   GET #2, , encoded
   i% = ASC(encoded)
   SELECT CASE i%
       CASE 0
           'do nothing
       CASE 13
           PRINT #3,
           'skip first char of next line
           IF NOT EOF(2) THEN
               GET #2, , encoded
               GET #2, , lineNum
               SEEK #2, SEEK(2) - 2
               lineNum = (lineNum AND &HFFFF&)
               IF (CHR$(0) = encoded) AND (&HFFFF& = lineNum) THEN
                   CLOSE : SYSTEM
               ELSEIF lineNum <> 0 THEN
                   PRINT #3, LTRIM$(STR$(lineNum)); " ";
               END IF
           END IF
       CASE &H8D
           'deal with encoded line numbers (GOTO targets)
           IF NOT EOF(2) THEN
               GET #2, , encoded
               IF NOT EOF(2) THEN
                   GET #2, , lineNum
                   SEEK #2, SEEK(2) - 2
                   lineNum = (lineNum AND &HFFFF&)
               ELSE
                   'should NEVER get here
                   lineNum = 0
               END IF
               lo& = ((ASC(encoded) * 4&) AND &HC0) XOR (lineNum AND 255&)           'LEFT SHIFT ASC(encoded), 2
               hi& = ((ASC(encoded) * 16&) AND &HC0) XOR ((lineNum \ 256&) AND 255&) 'LEFT SHIFT ASC(encoded), 4
               tmp = lo& + (hi& * 256&)
               PRINT #3, LTRIM$(RTRIM$(STR$(tmp)));
           END IF
       CASE ELSE
           IF keywords(i%) <> "" THEN
               PRINT #3, keywords(i%);
           ELSE
               PRINT #3, encoded;
           END IF
   END SELECT

LOOP CLOSE SYSTEM</lang>