Recursive Descent Parsing II

Expr.om

PROCEDURE ^ Expression() : BOOLEAN; PROCEDURE Factor() : BOOLEAN; (* Factor = "(" Expression ")" | ("+" | "-") Factor | Constant . *) BEGIN IF sy = "(" THEN GetSy; IF ~Expression() OR (sy # ")") THEN RETURN FALSE END; GetSy; RETURN TRUE ELSIF (sy = "+") OR (sy = "-") THEN GetSy; RETURN Factor() ELSE RETURN Constant() END; END Factor; PROCEDURE Term() : BOOLEAN; (* Term = Factor { ("*" | "/") Factor } . *) BEGIN IF ~Factor() THEN RETURN FALSE END; WHILE (sy = "*") OR (sy = "/") DO GetSy; (* skip operator *) IF ~Factor() THEN RETURN FALSE END; END; RETURN TRUE END Term;