collapseos/apps/forth/main.asm

; *** Const ***
; Base of the Return Stack
.equ	RS_ADDR		0xf000
; Number of bytes we keep as a padding between HERE and the scratchpad
.equ	PADDING		0x20
; Max length of dict entry names
.equ	NAMELEN		8
; Offset of the code link relative to the beginning of the word
.equ	CODELINK_OFFSET	10

; *** Variables ***
.equ	INITIAL_SP	FORTH_RAMSTART
.equ	CURRENT		@+2
.equ	HERE		@+2
.equ	INPUTPOS	@+2
; Buffer where we compile the current input line. Same size as STDIO_BUFSIZE.
.equ	COMPBUF		@+2
.equ	FORTH_RAMEND	@+0x40

; *** Code ***
forthMain:
	; STACK OVERFLOW PROTECTION:
	; To avoid having to check for stack underflow after each pop operation
	; (which can end up being prohibitive in terms of costs), we give
	; ourselves a nice 6 bytes buffer. 6 bytes because we seldom have words
	; requiring more than 3 items from the stack. Then, at each "exit" call
	; we check for stack underflow.
	push	af \ push af \ push af
	ld	(INITIAL_SP), sp
	ld	hl, CONSTANT		; last entry in hardcoded dict
	ld	(CURRENT), hl
	ld	hl, FORTH_RAMEND
	ld	(HERE), hl
forthRdLine:
	ld	hl, msgOk
	call	printstr
	call	printcrlf
	call	stdioReadLine
	ld	(INPUTPOS), hl
forthInterpret:
	ld	ix, RS_ADDR-2		; -2 because we inc-before-push
	ld	iy, INTERPRET+CODELINK_OFFSET
	jp	executeCodeLink
msgOk:
	.db	" ok", 0
apps/forth: new (WIP) application 2020-03-07 12:13:15 -05:00			`; * Const *`
			`; Base of the Return Stack`
			`.equ RS_ADDR 0xf000`
			`; Number of bytes we keep as a padding between HERE and the scratchpad`
			`.equ PADDING 0x20`
forth: add words "CREATE", "@", "!", "HERE", "QUIT" 2020-03-07 17:09:45 -05:00			`; Max length of dict entry names`
			`.equ NAMELEN 8`
apps/forth: new (WIP) application 2020-03-07 12:13:15 -05:00			`; Offset of the code link relative to the beginning of the word`
			`.equ CODELINK_OFFSET 10`

			`; * Variables *`
			`.equ INITIAL_SP FORTH_RAMSTART`
			`.equ CURRENT @+2`
			`.equ HERE @+2`
			`.equ INPUTPOS @+2`
forth: add words "CREATE", "@", "!", "HERE", "QUIT" 2020-03-07 17:09:45 -05:00			`; Buffer where we compile the current input line. Same size as STDIO_BUFSIZE.`
forth: simplify execution model and handle literals better This scheme of "when we handle line-by-line, compile one word at a time then execute" so that we could allow words like "CREATE" to call "readword" before continuing was a bad scheme. It made things like branching outside of a colon definition impossible. This commit implement a new "litWord". When an undefined word is encountered at compile time, it is included as-is in a string literal word. It is at run time that we decide what to do with it. 2020-03-09 08:49:51 -04:00			`.equ COMPBUF @+2`
forth: add words "CREATE", "@", "!", "HERE", "QUIT" 2020-03-07 17:09:45 -05:00			`.equ FORTH_RAMEND @+0x40`
apps/forth: new (WIP) application 2020-03-07 12:13:15 -05:00
			`; * Code *`
			`forthMain:`
forth: Check for PS underflow 2020-03-07 20:20:11 -05:00			`; STACK OVERFLOW PROTECTION:`
			`; To avoid having to check for stack underflow after each pop operation`
			`; (which can end up being prohibitive in terms of costs), we give`
			`; ourselves a nice 6 bytes buffer. 6 bytes because we seldom have words`
			`; requiring more than 3 items from the stack. Then, at each "exit" call`
			`; we check for stack underflow.`
			`push af \ push af \ push af`
apps/forth: new (WIP) application 2020-03-07 12:13:15 -05:00			`ld (INITIAL_SP), sp`
forth: add "DOES>" and "CONSTANT" 2020-03-07 22:18:14 -05:00			`ld hl, CONSTANT ; last entry in hardcoded dict`
apps/forth: new (WIP) application 2020-03-07 12:13:15 -05:00			`ld (CURRENT), hl`
			`ld hl, FORTH_RAMEND`
			`ld (HERE), hl`
forth: add words "CREATE", "@", "!", "HERE", "QUIT" 2020-03-07 17:09:45 -05:00			`forthRdLine:`
			`ld hl, msgOk`
			`call printstr`
			`call printcrlf`
			`call stdioReadLine`
			`ld (INPUTPOS), hl`
			`forthInterpret:`
forth: simplify execution model and handle literals better This scheme of "when we handle line-by-line, compile one word at a time then execute" so that we could allow words like "CREATE" to call "readword" before continuing was a bad scheme. It made things like branching outside of a colon definition impossible. This commit implement a new "litWord". When an undefined word is encountered at compile time, it is included as-is in a string literal word. It is at run time that we decide what to do with it. 2020-03-09 08:49:51 -04:00			`ld ix, RS_ADDR-2 ; -2 because we inc-before-push`
			`ld iy, INTERPRET+CODELINK_OFFSET`
apps/forth: new (WIP) application 2020-03-07 12:13:15 -05:00			`jp executeCodeLink`
forth: add words "CREATE", "@", "!", "HERE", "QUIT" 2020-03-07 17:09:45 -05:00			`msgOk:`
			`.db " ok", 0`