Micro assembly using scheme

mass.scm

;;(load "mass.scm")
(require-extension anaphora)
(require-extension holes)
(require-extension s)
(require-extension srfi-69)

(define program "MOV a 3
ADD a a -1
JNE 1 a 1")

;;; extract assembly instructions from the program
;;; s-split splits the instruction by space
;;; s-lines splits the program by line
(define asses (map (@> s-split " ") (s-lines program)))

(define registers (make-hash-table))

(define (set-dest register value)
  (hash-table-set! registers register value))

(define (get-src key)
  (aif (string->number key) ; try to convert string to number
       it ; succeeded. It must have been a number
       (hash-table-ref/default registers key 0))) ; must have been a register

;;; define the actions for an instruction
(define (MOV dest src)
  (set-dest dest (get-src src)))

(define (ADD dest src1 src2)
  (set-dest dest (+ (get-src src1) (get-src src2))))

(define (SUB dest src1 src2)
  (set-dest dest (- (get-src src1) (get-src src2))))

(define (JNE address src1 src2)
  (if (= (get-src src1) (get-src src2))
      #f ; no branching required, so just return false
      (string->number address))) ; branch required, return the address

;; run the machine
(let loop ((pc 0)) ; pc is the program counter
  (when (< pc (length asses)) ; keep running until the pc goes out of bounds
	(define ass (list-ref asses pc)) ; retrieve the instruction
	(define args (cdr ass)) ; ; the arguments of the instruction
	(case (string->symbol (car ass)) ; extract the command to be performed
	  [(MOV) (apply MOV args)]
	  [(ADD) (apply ADD args)]
	  [(SUB) (apply SUB args)]
	  [(JNE) (awhen (apply JNE args) (loop it))]
	  [else (print "didn't understand instruction")])
	(loop (+ 1 pc))))

(display "Register dump:")
(write (hash-table->alist registers))
(newline)

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