2010/3/19 国平张
Sorry. The same error, This is new stuff.
Ah indeed - I didn't spot that one as I only read the code rather than ran it. With the change the parser type to use /newtype/ all the primitive parsers have to be encoded inside the newtype's constructor (primitive parsers being ones that have to look directly at the input stream). item :: Parser Char item = Parser $ \inp -> case inp of [] -> [] (x:xs) -> [(x,xs)] Or in a more prosaic style item :: Parser Char item = Parser (\inp -> case inp of [] -> [] (x:xs) -> [(x,xs)]) This is slightly tiresome. Fortunately once you have defined a small set of primitive parsers, many more parsers can be "derived" by combining the primitives rather than looking at the input stream - this is the power of the monadic style. The p parser you defined with the do ... notation is one such derived parser. Best wishes Stephen