addn.asm

Instruction Set:
PSH C   push a constant onto the stack
POP N   remove N values from the top of the stack
POP     pop value N, POP N
STO N   pop value, store into Nth slot down in the stack
STO     pop value N, STO N
RCL N   push value in Nth slot down in the stack
RCL     pop value N, RCL N
AND C   logical AND C with the top value
AND     logical AND the top two values
NOT     complement the top value
JMP A   execute at address A
JMP     execute at address in the top two values
EXE A   push address of next instruction, JMP A
EXE     push address of next instruction, JMP
CND     skip following instruction if top value is greater than zero
ADD C   add C to top value
ADD     add top two values
SUB C   subtract C from top value
SUB     subtract top two values
ADR     push address of next instruction

Following is an example program for the ADDN function, which adds N numbers together and returns their sum.
PSH #x01
PSH #x02
PSH #x03 ; arguments to ADDN, (1 2 3)
PSH #x03 ; number of args, 3

PSH #x10
PSH #x00 ; push address of ADDN, call it 
EXE

JMP #x0e ; infinite loop, end of program

RCL #x02 ; start of ADDN, recall # of args
ADD #x04 
STO #x03 ; add 4 and restore to make arg index
PSH #x00 ; addition accumulator

RCL #x03 ; start of loop, recall arg index (used to be # of args)
RCL #x00 ; duplicate it
SUB #x04
CND
JMP #x2e ; goto END if arg index <= 4
RCL
ADD
RCL #x03 ; get num at arg index, add to accumulator (prev 2 lines), recall arg index again
SUB #x01
STO #x04 ; decrement and restore
JMP #x18 ; goto start of loop

RCL #x01 ; END of loop, recall accumulator
STO #x05 ; store underneath return address
POP #x02 ; get rid of remaining locals, jump to return address
JMP