Shunting-Yard

#define bcall(x) rst 28h \ .dw x
saveSScreen = 86ECh
scrap=saveSScreen
outhead=8000h
stackhead = 8002h
.db $BB,$6D
.org $9D95
    ld hl,test
    ld bc,test_end-test
    call shuntingyard
    call rpn
    ld hl,scrap
    bcall(450Ah)
    bcall(452Eh)
    ret
shuntingyard:
    ld de,scrap
    ld (outhead),de
    ld d,(scrap/256)+3
    ld (stackhead),de
_:
    ld a,(hl)
    call +_
    cpi
    jp pe,-_
    ld hl,scrap+768
    ld de,(stackhead)
    or a
    sbc hl,de
    ld b,h
    ld c,l
    ld hl,(outhead)
    ex de,hl
    jr z,$+3
    ldir
    dec de
    xor a
    ld (de),a
    ret
_:
    cp '.'
    jp z,num_dec
    cp 30h
    jr c,+_
    cp 3Ah
    jp c,num
_:
    cp '('
    jp nz,+_
    ex de,hl
    ld hl,(stackhead)
    dec hl
    ld (hl),','
    dec hl
    ld (hl),a
    ld (stackhead),hl
    ex de,hl
    ret
_:
    cp ')'
    jp nz,checkunops
    push hl
    push bc
    ld hl,scrap+768
    ld de,(stackhead)
    sbc hl,de
    jp z,ERR_Unmatched_lparens
    ld b,h
    ld c,l
    ex de,hl
    ld de,(outhead)
;BC is the size of the stack. Use this in case there is a missing ')' so we don't read garbage.
;basically search for the matching '(' while piping out the stack to the output.
outerloop:
    ld a,(hl)
    cp '('
    jr z,parens_found
    ld a,','
_:
    cp (hl)
    ldi
    jp po,ERR_Unmatched_lparens
    jr z,outerloop
    jp -_
parens_found:
    inc hl
    inc hl
    ld (outhead),de
    ld (stackhead),hl
    pop bc
    pop hl
    ret
checkunops:
checkbinops:
;;  if the token is an operator, then:
;;      while there is an operator at the top of the operator stack with
;;          greater than or equal to precedence and the operator is left associative:
;;              pop operators from the operator stack, onto the output queue.
;;      push the read operator onto the operator stack.
;;
;;
    push bc
    ex de,hl
    call getprecedence
    ld a,c
    pop bc
    ex de,hl
    jp c,search_function
    ;now C is the precedence, with lower bit = 1 if left-associative
    push bc
    push hl
    ld de,(stackhead)
    ld hl,scrap+768
    sbc hl,de
    ld b,h
    ld c,l
    ld hl,(outhead)
    ex de,hl
    jr z,pushop
    ;a is the precedence against which to compare
_:
    push hl
    push bc
    push af
    ld a,(hl)
    call getprecedence
    jr c,+_
    pop hl
    ld a,h      ;incoming
    cp c
    jr nz,$+4
    rra \ nop

    pop bc
    pop hl

 ;======================================================
    jr nc,pushop
.echo "The following code only works until we have to add >1 byte tokens."
 ldi
 ldi
    jp pe,-_
    jp $+6
_:
    pop af
    pop bc
    pop hl
pushop:
    ld (outhead),de
    pop de
    dec hl
    ld (hl),','
    dec hl
    ld a,(de)
    ld (stackhead),hl
    ld (hl),a
    ex de,hl
    pop bc
    ret
search_function:
    jp ERR_Func_Not_Found
getprecedence:
    ld hl,binops
    ld b,(binops_end-binops)/2
_:
    cp (hl)
    inc hl
    ld c,(hl)
    ret z
    inc hl
    djnz -_
    scf
    ret
binops:
    .db 4,  $01
    .db '=',$50
    .db '|',$60
    .db '&',$70
    .db '-',$81     ;right associative
    .db '+',$80     ;left associative
    .db '/',$83     ;right associative
    .db '*',$82     ;left associative
    .db '^',$85     ;right associative
binops_end:
num:
    ld de,(outhead)
_:
    ldi
    jp po,+_
    ld a,(hl)
    cp '.'
    jr z,num_dec+4
    cp 30h
    jr c,+_
    cp 3Ah
    jr c,-_
_:
    ld a,','
    ld (de),a
    inc de
    ld (outhead),de
    dec hl
    inc bc
    ret
num_dec:
    ld de,(outhead)
_:
    ldi
    jp po,+_
    ld a,(hl)
    cp 30h
    jr c,+_
    cp 3Ah
    jr c,-_
_:
    cp '.'
    jp z,ERR_Syntax_00
    ld a,','
    ld (de),a
    inc de
    ld (outhead),de
    dec hl
    inc bc
    ret
ERR_Syntax_00:      ;Too many decimal points.
ERR_Func_Not_Found:
ERR_Unmatched_lparens:
    ret
rpn:
    ret
test:
;    .db "(3.1415926535)"
.db "(3.142+6/2-7)*3^6*3"
test_end: