Re: [Haskell-cafe] please comment on my parser, can I do this cleaner?

Thanks. It seems my original parser also works against FOO,BAR,BAZ if you only modify atom = string ","           <|> ( many1 $ noneOf "()<>," ) -- add , Indeed, what to call the "thingies" in a parser is a source of some personal consternation. What is a token, what is an atom, what is an expr? It all seems to be somewhat ad hoc.

2009/6/9 Daniel Fischer :

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Am Dienstag 09 Juni 2009 20:29:09 schrieb Thomas Hartman:

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All I want to do is split on commas, but not the commas inside () or <> tags.

I have been wanting to master parsec for a long time and this simple exercise looked like a good place to start.

The code below does the right thing. Am I missing any tricks to make this simpler/neater?

Thanks, thomas.

thartman@ubuntu:~/perlArena>cat splitEm. splitEm.hs   splitEm.hs~  splitEm.pl   splitEm.pl~ thartman@ubuntu:~/perlArena>cat splitEm.hs {-# LANGUAGE ScopedTypeVariables #-} import Text.ParserCombinators.Parsec import Text.ParserCombinators.Parsec.Char import Text.PrettyPrint (vcat, render, text) import Data.List.Split hiding (sepBy, chunk) import Text.ParserCombinators.Parsec.Token

import Debug.Trace import Debug.Trace.Helpers

-- this works, but is there a neater/cleaner way? main = ripInputsXs (toEof splitter) "splitter" [ goodS, badS ]

-- I need a way to split on commas, but not the commas inside '<>' or '()' characters goodS = "<*2>FOO<2,1>,<*3>(SigB<8:0:2>,BAR),<*2>Siga<2:0>,Sigb<8,7,6,5,0>" badS = "<*2)FOO<2,1>,<*3>(SigB<8:0:2>,BAR),<*2>Siga<2:0>,Sigb<8,7,6,5,0>" -- the first < matches a ), so reject this

splitter = do   chunks :: [String] <- toEof (many chunk)   let pieces = map concat $ splitOn [","] chunks   return pieces -- chunks   where     atom = string ","            <|> ( many1 $ noneOf "()<>" )     chunk = parenExpr <|>  atom

I think that does not do what you want.

For input "FOO,BAR,BAZ", chunks is ["FOO,BAR,BAZ"], that won't be split; as far as I can see, it splits only on commas directly following a parenExpr (or at the beginning of the input or directly following another splitting comma).

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    parenExpr :: GenParser Char st [Char]     parenExpr = let paren p = betweenInc (char '(' ) (char ')' ) p                                 <|> betweenInc (char '<' ) (char '>' ) p                 in paren $ option "" $ do ps <- many1 $ parenExpr <|> atom                                           return . concat $ ps

betweenInc o' c' p' = do   o <- o'   p <- p'   c <- c'   return $ [o] ++ p ++ [c]

toEof p' = do         r <- p'         eof         return r

ripInputs prs prsName xs = mapM_ (putStrLn . show . parse prs prsName ) xs ripInputsXs prs prsName xs = mapM_ (putStrLn . showXs . parse prs prsName ) xs where showXs v = case v of           Left e -> show e           Right xs -> render . vcat . map text $ xs

I can offer (sorry for the names, and I don't know if what that does is really what you want):

keepSepBy :: Parser a -> Parser a -> Parser [a] keepSepBy p sep = (do    r <- p    (do s <- sep        xs <- keepSepBy p sep        return (r:s:xs)) <|> return [r])    <|> return []

twain :: Parser a -> Parser a -> Parser [a] -> Parser [a] twain open close list = do    o <- open    l <- list    c <- close    return (o:l++[c])

comma :: Parser String comma = string ","

simpleChar :: Parser Char simpleChar = noneOf "<>(),"

suite :: Parser String suite = many1 simpleChar

atom :: Parser String atom = fmap concat $ many1 (parenExp <|> suite)

parenGroup :: Parser String parenGroup = fmap concat $ keepSepBy atom comma

parenExp :: Parser String parenExp = twain (char '<') (char '>') parenGroup            <|> twain (char '(') (char ')') parenGroup

chunks :: Parser [String] chunks = sepBy atom comma

splitter = do    cs <- chunks    eof    return cs

goodS = "<*2>FOO<2,1>,<*3>(SigB<8:0:2>,BAR),<*2>Siga<2:0>,Sigb<8,7,6,5,0>" badS = "<*2)FOO<2,1>,<*3>(SigB<8:0:2>,BAR),<*2>Siga<2:0>,Sigb<8,7,6,5,0>"

goodRes = parse splitter "splitter" goodS badRes = parse splitter "splitter" badS

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