On Tue, Feb 12, 2013 at 4:38 PM, Sean Cormican
name :: Expression name = ID "string"
number :: Expression number = Num 123
whileParser :: Parser Expression whileParser = whiteSpace >> expr8
expr8 :: Parser Expression expr8 = name <|> number
You have defined name to be an Expression. But <|> composes *parsers*, not expressions. To create a Parser Expression, you would be composing (Parser Expression)s, not simply (Expression)s; so you don't want "name" to be simply an Expression, but a Parser that parses an input String and produces an Expression, something like name :: Parser Expression name = ID <*> identifier -- parse an identifier, wrap it in an ID number :: Parser Expression number = Num <*> integer -- parse an integer, wrap it in a Num -- brandon s allbery kf8nh sine nomine associates allbery.b@gmail.com ballbery@sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net