grammar

# outdated file
program := (
	|function SEMICOLON?
	|EXTERN IDENTIFIER LPAREN 
		(IDENTIFIER COLON IDENTIFIER)? 
		(COMMA TYPE_ANNOT)* RPAREN ARROW IDENTIFIER
)*

function := 
	DEF IDENTIFIER LPAREN 
	(
		IDENTIFIER COLON IDENTIFIER 
		(COMMA TYPE_ANNOT)* RPAREN ARROW IDENTIFIER LBRACE) 
		|(IDENTIFIER COLON IDENTIFIER)?
	) (
		|expression SEMICOLON
	)* RBRACE

expression :=
	|(MINUS | PLUS | NOT) expression # Unary
	|LPAREN expression RPAREN # Parenthesised expr
	|expression (
		|PLUS|MINUS
		|DIV|MUL
		|LESS|LESSEQ
		|GREATER|GREATEREQ
		|NOTEQ|EQUAL
		|PLUSEQ|MINUSEQ
		|DIVEQ|MULEQ
		|ASSIGN
		) expression # Binary Op
	|IF LPAREN expression RPAREN expression (ELSE expression)? # If else
	|INT
	|STR
	|IDENTIFIER LPAREN expression? (COMMA expression)* RPAREN # Function call
	|IDENTIFIER
	|TRUE
	|FALSE
	|LET expression COLON IDENTIFIER
	|RETURN expression



class :=
	CLASS LBRACE *(function) RBRACE