PROG	=	FDEF ...
FDEF	=	IDEN '(' [IDEN ... ','] ')' STATS

EXP		=	EXP_3  [('=')									EXP]
EXP_3	=	EXP_2  [('&&' | '||')							EXP_3]
EXP_2	=	EXP_1  [('<' | '>' | '<=' | '>=' | '==' | '!=') EXP_2]
EXP_1	=	EXP_0  [('+' | '-')								EXP_1]
EXP_0	=	FACTOR [('*' | '/' | '%')						EXP_0]

FACTOR	=	'(' EXP ')'								|
			'[' [EXP ... ',' ] ']'					|
			IDEN '[' EXP ']'						|
			IDEN ['(' [EXP... ',' ] ')']			|
			[('-' | '!')]<NUM>						|
			<STR>
			
STAT	=	EXP										|
			STATS									|
			['var'] IDENT ['[' EXP ']'] ['=' EXP]	|
			IF										|
			WHILE									|
			RET
			
STATS	=	'{' [STAT ';' ... ] '}'

IF		=	'if' '(' EXP ')' STAT ['else' STAT]
WHILE	=	'while' '(' EXP ')' STAT
RET		=	'return' [EXP]