Thanks Christian, I adapted the "keyword" parser and now "n" <-> "negi" does not occur. But there are still other problems to solve. If I activate the parseFunction the parser will answer to fact.gml unexpected end of input, expecting space or "}". Any ideas? -----Ursprüngliche Nachricht----- Von: Christian Maeder [mailto:Christian.Maeder@dfki.de] Gesendet: Montag, 7. März 2011 12:23 An: Hauschild, Klaus (EXT) Cc: haskell-cafe@haskell.org Betreff: Re: Overlaping Parsec rules You should parse keywords using: keyword s = try (string s) >> notFollowedBy (letter <|> digit) C. Am 07.03.2011 11:34, schrieb Hauschild, Klaus (EXT):
Hi,
to solve this ICFP task _http://www.cs.cornell.edu/icfp/task.htm_ I'm currnetly working on the parser. With the hint from Thu (reading Phillip Wadlers monadic parser paper) and consulting _http://en.wikibooks.org/wiki/Write_Yourself_a_Scheme_in_48_Hours/Parsing_ I produce a first working version of the parser. After this great moment I completed the token definition and near all parsing rules. For the complete code have a look at _http://code.google.com/p/hgmltracer/source/browse/#svn%2Ftrunk%2FhGmlTracer_
data GmlToken =
-- structures
FunctionToken TokenSequence |
ArrayToken TokenSequence |
-- control operators
ApplyToken |
IfToken |
-- number operators
AddiToken |
AddfToken |
ACosToken |
ASinToken |
ClampfToken |
CosToken |
DiviToken |
DivfToken |
EqiToken |
EqfToken |
FloorToken |
FracToken |
LessiToken |
LessfToken |
ModiToken |
MuliToken |
MulfToken |
NegiToken |
NegfToken |
ToRealToken |
SinToken |
SqrtToken |
SubiToken |
SubfToken |
-- points
GetXToken |
GetYToken |
GetZToken |
PointToken |
-- arrays
GetToken |
LengthToken |
-- environment
IdentifierToken String |
BinderToken String |
-- types
BoolToken Bool |
IntToken Int |
RealToken Double |
StringToken String deriving Show
And
parseGml :: String -> [GmlToken]
parseGml input = case parse parseList "gml" input of
Left err -> error ("Parse error: " ++ (show err))
Right gml -> gml
parseList = sepBy parseGml' spaces
parseGml' =
-- structures
-- parseFunction
-- <|> parseArray
-- control operators
parseControlOperators
-- number operators
<|> parseNumberOperators
-- points
<|> parsePointOperators
-- arrays
<|> parseArrayOperators
-- types
<|> parseBool
<|> parseInteger
<|> parseString
-- environment
<|> parseIdentifier
<|> parseBinder
parseArray = parseSequence '[' ']'
parseFunction = parseSequence '{' '}'
parseSequence start end = do char start
array <- parseList
char end
return $ ArrayToken array
parseControlOperators = parseApply <|> parseIf
parseApply = do string "apply"
return $ ApplyToken
parseIf = do string "if"
return $ IfToken
parseNumberOperators = do string "addi"
return $ AddiToken
<|> do string "addf"
return $ AddfToken
<|> do string "acos"
return $ ACosToken
<|> do string "asind"
return $ ASinToken
<|> do string "clampf"
return $ ClampfToken
<|> do string "cos"
return $ CosToken
<|> do string "divi"
return $ DiviToken
<|> do string "divf"
return $ DivfToken
<|> do string "eqi"
return $ EqiToken
<|> do string "eqf"
return $ EqfToken
<|> do string "floor"
return $ FloorToken
<|> do string "frac"
return $ FracToken
<|> do string "lessi"
return $ LessiToken
<|> do string "lessf"
return $ LessfToken
<|> do string "modi"
return $ ModiToken
<|> do string "muli"
return $ MuliToken
<|> do string "mulf"
return $ MulfToken
<|> do string "negi"
return $ NegiToken
<|> do string "negf"
return $ NegfToken
<|> do string "real"
return $ ToRealToken
<|> do string "sin"
return $ SinToken
<|> do string "Sqrt"
return $ SqrtToken
<|> do string "subi"
return $ SubiToken
<|> do string "subf"
return $ SubfToken
parsePointOperators = do string "getx"
return $ GetXToken
<|> do string "gety"
return $ GetYToken
<|> do string "getz"
return $ GetZToken
<|> do string "point"
return $ PointToken
parseArrayOperators = do string "get"
return $ GetToken
<|> do string "length"
return $ LengthToken
parseInteger = liftM (IntToken . read) $ many1 digit
parseBool = do string "true"
return $ BoolToken True
<|> do string "false"
return $ BoolToken False
parseString = do char '"'
string <- many (noneOf "\"")
char '"'
return $ StringToken string
parseIdentifier = do identifier <- many (noneOf " ")
return $ IdentifierToken identifier
parseBinder = do char '/'
binder <- many (noneOf " ")
return $ BinderToken binder
parseComment = do char '%'
many (noneOf "")
newline
return $ ()
spaces = skipMany1 space
After gluing all this together in my mind all worked well. But it doesn't. The test file for parsing looks like:
{ /self /n n 2 lessi { 1 } { n 1 subi self self apply n muli } if } /fact
12 fact fact apply
* I think there is a problem with overlaping rules. There is a parser rule consuming "negi" and resulting in the NegiToken. A single "n" is a valid identifier. For the example file my parser says: unexpected " ", expecting "negi" * I think the same problem is present for "parseInteger" and "parseReal" (currently no in code but looks like "parseReal = do a <- many1 digit \n char '.' \n b <- many1 digit \n return $ RealToken (read (a ++ "." ++ b)" * Something with "parseFunction" is going really wrong. * All parsig rules are designed with the condition that each "construct" is separated by whitespaces. For this before parsing the input will be preprocessed: insert spaces, removing whitespaces and so on. Now in the parsed result appears (IdentifierToken ""). I think my version is not the best way to parse a identifer:
parseIdentifier = *do* identifier <- many (noneOf " ") return $ *IdentifierToken* identifier
Please help me.
Klaus
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