interpreter

Basic stack-based interpreter for APT Lecture.

Runs with one stack, and a program counter (pc), that starts at 0.

Running

Compile all three classes, then run Interpreter with one argument, your input file.

For example: java Interpreter myfile.swl

Instructions

Name	Description
PRINT	Prints the top element
INT x	Pushes integer x to stack
ADD	Adds the top two elements
SUB	Subtracts the top two elements
SWAP	Swaps the two top elements
DUP	Duplicates top element
POP	Pops top element from stack (effectively just removes it)
JGE x	If top element is >=0, jump to x
JEQ x	If top element is ==0, jump to x
CALL x	Push pc+1 to stack, jump to x
RET	Pop top element, jump to it

Lines can also be preceded by labels, the format for this is LABEL: INSTRUCTION

(note the space between the colon and the instruction)

Example file

INT 100
L1: PRINT
INT 1
SUB
JGE L1