(1) show contents of file "fac.txt":
======================================================================

$ cat fac.txt



        fac(n) {
                f = 1;
                while (n > 1) {
                        f = f*n;
                        n = n - 1;
                }
                return(f);
        }

        print fac(4);


(2) interpret & compile file "fac.txt"
======================================================================

$ scryer-prolog -g "run_file('fac.txt')" interp.pl


        tokens:

        [id(fac),(,id(n),),{,id(f),=,num(1),;,while,(,id(n),rop(>),num(1),),{,id(f),=,id(f),mop(*),id(n),;,id(n),=,id(n),aop(-),num(1),;,},return,(,id(f),),;,},print,id(fac),(,num(4),),;]

        AST:

        sequence(function(fac,n,sequence(assign(f,n(1)),sequence(while(bin(>,v(n),n(1)),sequence(assign(f,bin(*,v(f),v(n))),assign(n,bin(-,v(n),n(1))))),return(v(f))))),print(call(fac,n(4))))


        VM code:

            0:   jmp 33
            2:   alloc 1
            4:   pushc 1
            6:   pop 1
            8:   pushv 0
           10:   pushc 1
           12:   jle 30
           14:   pushv 1
           16:   pushv 0
           18:   mul
           19:   pop 1
           21:   pushv 0
           23:   pushc 1
           25:   sub
           26:   pop 0
           28:   jmp 8
           30:   pushv 1
           32:   ret
           33:   pushc 4
           35:   call 2
           37:   print
           38:   halt

        intcode:

        [9,33,1,1,2,1,4,1,3,0,2,1,12,30,3,1,3,0,7,4,1,3,0,2,1,6,4,0,9,8,3,1,15,2,4,13,2,14,0]

        program output:

        24


(3) feed generated integer code to VM implementation in Haskell
======================================================================
$ hugs vm.hs


        Main> main
        [9,33,1,1,2,1,4,1,3,0,2,1,12,30,3,1,3,0,7,4,1,3,0,2,1,6,4,0,9,8,3,1,15,2,4,13,2,14,0]
        24


(4) extract integers
======================================================================

$ echo "[9,33,1,1,2,1,4,1,3,0,2,1,12,30,3,1,3,0,7,4,1,3,0,2,1,6,4,0,9,8,3,1,15,2,4,13,2,14,0]" | tr -d "[]" | sed -e "s/,/ /g"

        9 33 1 1 2 1 4 1 3 0 2 1 12 30 3 1 3 0 7 4 1 3 0 2 1 6 4 0 9 8 3 1 15 2 4 13 2 14 0


(5) feed integer code to VM implementation in J
======================================================================

$ (echo "instrs =: 9 33 1 1 2 1 4 1 3 0 2 1 12 30 3 1 3 0 7 4 1 3 0 2 1 6 4 0 9 8 3 1 15 2 4 13 2 14 0"; cat vm.ijs) | ~/j601/jconsole

                         24