quiz 2  summer

the asm language

r1 add r2
1 set r3
10 jmp
2 add r1


grammar

asm -> arg asm | EOF
arg -> reg op reg
arg -> num op2
op2 -> op reg
op2 -> JMP
op -> ADD | SUB | SET

parser

asm()
  if match('EOF')
    ret 1
  else
    arg()
    asm()
  
arg()
  if reg()
    op()
    reg()
    ret 1
  if num()
    op2()
    ret 1
  ret 0

op2()
  if op()
    reg()
  if match('JMP')
    ret 1
  ret 0

op()
  if match('ADD')
    ret 1
  if match('SUB')
    ret 1
  if match('SET')
    ret 1
  ret 0

reg()
  recognise r0..r7
  
num() 
  recognise integer

an example of asm program to do 1+2+3

1 set r1
2 set r2
3 set r3
0 set r4
r1 add r4
r2 add r4
r3 add r4

26 june 2018