On Mon, May 5, 2008 at 3:40 AM, Ross Boylan
I am new to Haskell and Parsec, and am trying to understand both. I tried to follow the example of how to use Parsec to parse TeX begin/end groups, but can't get it to run. I'm using HUGS -98 on Debian.
When I copied the code I got errors about unknown terms (reserved and braces). I've tried to get them from the lexer, but now get this error :load grammar.hsl ERROR "grammar.hsl":21 - Type error in explicitly typed binding *** Term : envEnd *** Type : String -> GenParser Char a [Char] *** Does not match : String -> Parser ()
Can anyone help me understand what the problem is?
Here's the code the caused the above error; I believe the part after --TeX example is verbatim from the Parsec documentation. I picked haskell as the language for to lexer "arbitrarily."
import Text.ParserCombinators.Parsec import qualified Text.ParserCombinators.Parsec.Token as P import Text.ParserCombinators.Parsec.Language(haskell) reserved = P.reserved haskell braces = P.braces haskell
-- TeX example environment = do{ name <- envBegin ; environment ; envEnd name } <|> return ()
envBegin :: Parser String envBegin = do{ reserved "\\begin" ; braces (many1 letter) }
envEnd :: String -> Parser () envEnd name = do{ reserved "\\end" ; braces (string name) }
My guess is the following: string :: String -> Parser String braces :: Parser a -> Parser a Meaning braces (string name) :: Parser String Which is not the same as your declared return type Parser (). Add a return () at the end of envEnd.
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