.if cond statments .elsif statments .endif
cond: | exp
      | cond || exp (logical or)

exp: | term
     | exp && term (logical and)

term: | abs
      | !abs (logical not)

abs: | (cond)
     | group

group: | expr BinOp expr
       | flag
       | expr

BinOp: | == 
       | != 
       | > 
       | >= 
       | < 
       | <= 
       | &

flag: | zero?
      | carry?
      | overflow?
      | sign?
      | parity?