A recursive descent parser for ASM language

Let us begin with defining a language, a simple assembly language (invent by Tawan).  We show a sample of the code.

CLRA
MOV R1,100
MOV R2,200
ADD R1
ADD R2
MOVA R1

Grammar of ASM

asm = op oprnd asm | EOF
op = CLRA | MOV | ADD | MOVA
oprnd = reg , num | reg | empty
reg = R[0..31]

Parser

return 0 - error, 1 - OK

reg()
  match('R')
  ret num()

op()
  switch tokentype()
    mov: match('MOV')
    ...
    default: ret 0

oprnd()
  if reg() != 0     
     if token == ','    //  lookahead
        match(',')
        ret num()
     else
        ret 1
   ret 1

asm()
   if token == EOF  ret 1
   if op() != 0
      oprnd()
      asm()
   ret 0

 Actual code in C

I modify my rz33-1 compiler.  I use its scanner which can accept lexemes of ASM easily.  Then, I put ASM parser into work.  Here is the whole package.   Please try to compile and run it. 

Enjoy!

last update 5 Sept 2017