Here is a new assembly language:  (don't worry about comment)

R1 add R2	;   R1 + R2 -> R2
10 set R3	;   10 -> R3
20 Jmp		;   jump to address 20
R4 sub R1	;   R4 - R1 -> R1
1 add R2	;   R2 + 1 -> R2


1) write Grammar for this language
2) write pseudo code for recursive descent parser of this grammar
3) use this language to write a program to add 1 + 2 + 3