r2000-analyze-basic

Analyze BASIC Tokens Workflow

Use this skill when the user asks to:

• "analyze this BASIC code"
• "decode basic commands from memory"
• "create side comments for BASIC lines"
• "parse basic pointer address and line number"

1. Determine Memory Range

Identify the starting and ending addresses of the Commodore BASIC sequence from the user's request or cross-references. If unspecified, prompt the user for clarification.

2. Read Memory Buffer

Invoke the r2000_read_region tool to read the requested sequence:

• start_address: The sequence start address (decimal).
• end_address: The sequence end address (decimal).
• view: "hexdump"

3. Process BASIC Lines

Commodore BASIC programs follow a strict structured sequence in memory. Iterate through the lines starting from the initial address, following the "Next Line Pointer" until you reach the end of the program.

Line Anatomy

1. Bytes 0–1 (Next Line Pointer): Pointer to the memory address where the next BASIC line begins, stored in Little Endian format (e.g., 24 04 $\rightarrow$ `$0424$).
2. Bytes 2–3 (Line Number): The BASIC line number as a 16-bit integer in Little Endian format (e.g., 0A 00 $\rightarrow$ 10).
3. Bytes 4–N (Tokens): The tokenized BASIC command. This sequence of bytes continues until a $00 (null) terminator is encountered.
4. Termination: The program ends when the "Next Line Pointer" (Bytes 0–1) of a line is $00 $00.

Keyword Token Table (V2)

Bytes in step 3 with the high-bit set ($80 to $CB) are keyword tokens. Decode them against this table:

Hex	Keyword	Hex	Keyword	Hex	Keyword	Hex	Keyword
$80	END	$93	LOAD	$A6	SPC(	$B9	POS
$81	FOR	$94	SAVE	$A7	THEN	$BA	SQR
$82	NEXT	$95	VERIFY	$A8	NOT	$BB	RND
$83	DATA	$96	DEF	$A9	STEP	$BC	LOG
$84	INPUT#	$97	POKE	$AA	+	$BD	EXP
$85	INPUT	$98	PRINT#	$AB	-	$BE	COS
$86	DIM	$99	PRINT	$AC	*	$BF	SIN
$87	READ	$9A	CONT	$AD	/	$C0	TAN
$88	LET	$9B	LIST	$AE	^	$C1	ATN
$89	GOTO	$9C	CLR	$AF	AND	$C2	PEEK
$8A	RUN	$9D	CMD	$B0	OR	$C3	LEN
$8B	IF	$9E	SYS	$B1	>	$C4	STR$
$8C	RESTORE	$9F	OPEN	$B2	=	$C5	VAL
$8D	GOSUB	$A0	CLOSE	$B3	<	$C6	ASC
$8E	RETURN	$A1	GET	$B4	SGN	$C7	CHR$
$8F	REM	$A2	NEW	$B5	INT	$C8	LEFT$
$90	STOP	$A3	TAB(	$B6	ABS	$C9	RIGHT$
$91	ON	$A4	TO	$B7	USR	$CA	MID$
$92	WAIT	$A5	FN	$B8	FRE	$CB	GO