[Haskell-cafe] Parsec problem

[Neil Mitchell]

Hi,

I'm using parsec to parse something which is either a "name" or a
"type". The particular test string I'm using is a type, but isn't a
name. I want things to default to "name" before "type".

Some examples of the parsec function, and the result when applied to a
test string:

> parsecQuery = do spaces ; types
Right Query {scope = [], names = [], typeSig = Just [a], items = [], flags = []}

> parsecQuery = do spaces ; names
Left (line 1, column 1):
unexpected "["
expecting white space, "--", "/", "(", letter, "::" or end of input

> parsecQuery = do spaces ; try names <|> types
Left (line 1, column 1):
unexpected "["
expecting white space, "--", "/", "(", letter, "::" or end of input

I would have expected try names <|> types to return a Right (since
types matches), but it doesn't. I assumed this would be a property of
Parsec, but it doesn't appear to hold. Can anyone shed any light?

Thanks

Neil