--------------------------------------------------------------------------- -- A simple example for the use of the functional logic parser combinators: -- We define a parser for arithmetic expressions over natural numbers. -- The presentation of this parser is the value of the expression. import Parser import Char expression = term t <*> plus_minus op <*> expression e >>> (op t e) <||> term where op,t,e free term = factor f <*> prod_div op <*> term t >>> (op f t) <||> factor where op,f,t free factor = terminal '(' <*> expression e <*> terminal ')' >>> e <||> num where e free plus_minus = terminal '+' >>> (+) <||> terminal '-' >>> (-) prod_div = terminal '*' >>> (*) <||> terminal '/' >>> div num = some digit l >>> numeric_value l where l free numeric_value ds = foldl1 ((+) . (10*)) (map (\c->ord c - ord '0') ds) digit = satisfy isDigit -- example application: expression val "(10+5*2)/4" =:= [] where val free