; *** Variables ***
; A list of words for each member of the A-Z range.
equ VAR_TBL VAR_RAMSTART
equ VAR_RAMEND @+52
; *** Code ***
varInit:
ld b, VAR_RAMEND-VAR_RAMSTART
ld hl, VAR_RAMSTART
xor a
loop:
ld (hl), a
inc hl
djnz .loop
ret
; Check if A is a valid variable letter (a-z or A-Z). If it is, set A to a
; valid VAR_TBL index and set Z. Otherwise, unset Z (and A is destroyed)
varChk:
call upcase
sub 'A'
ret c ; Z unset
cp 27 ; 'Z' + 1
jr c, .isVar
; A > 'Z'
dec a ; unset Z
ret
isVar:
cp a ; set Z
ret
; Try to interpret line at (HL) and see if it's a variable assignment. If it
; is, proceed with the assignment and set Z. Otherwise, NZ.
varTryAssign:
inc hl
ld a, (hl)
dec hl
cp '='
ret nz
ld a, (hl)
call varChk
ret nz
; We have a variable! Its table index is currently in A.
push ix ; --> lvl 1
push hl ; --> lvl 2
push de ; --> lvl 3
push af ; --> lvl 4. save for later
; Let's put that expression to read in scratchpad
inc hl \ inc hl
ld de, SCRATCHPAD
call rdWord
ex de, hl
; Now, evaluate that expression now in (HL)
call parseExpr ; --> number in DE
jr nz, .exprErr
pop af ; <-- lvl 4
call varAssign
xor a ; ensure Z
end:
pop de ; <-- lvl 3
pop hl ; <-- lvl 2
pop ix ; <-- lvl 1
ret
exprErr:
pop af ; <-- lvl 4
jr .end
; Given a variable **index** in A (call varChk to transform) and a value in
; DE, assign that value in the proper cell in VAR_TBL.
; No checks are made.
varAssign:
push hl
add a, a ; * 2 because each element is a word
ld hl, VAR_TBL
call addHL
; HL placed, write number
ld (hl), e
inc hl
ld (hl), d
pop hl
ret
; Check if value at (HL) is a variable. If yes, returns its associated value.
; Otherwise, jump to parseLiteral.
parseLiteralOrVar:
call isLiteralPrefix
jp z, parseLiteral
; not a literal, try var
ld a, (hl)
call varChk
ret nz
; It's a variable, resolve!
add a, a ; * 2 because each element is a word
push hl ; --> lvl 1
ld hl, VAR_TBL
call addHL
ld e, (hl)
inc hl
ld d, (hl)
pop hl ; <-- lvl 1
inc hl ; point to char after variable
cp a ; ensure Z
ret
