Re: [Haskell-cafe] a question about import and parsec...
Am Donnerstag, 21. April 2005 03:58 schrieb Greg Wolff:
I'm new at using Haskell and I'm trying to make use of the parsec
library. I've started by working through the examples in the user guide
which don't work as written in ghci when I run them. I've made
modifications that have gotten them working, up to a point. But now I
have an error one of the examples that has me stumped and looking in the
documentation didn't help.
When I run the following code without the import Data.Char I get an
error that digitToInt is not defined. When I put the import in I get a
large number of errors that weren't there before.
They were there, only ghci stopped on encountering an undefined name and
didn't look for all errors then.
The errors are all of the same kind, 'lexeme', 'identifier', 'symbol' and
'semi' - I hope, I haven't overlooked one - are named fields of a TokenParser
and you try to apply lexeme to a Parser Int. If you insert 'lang' in the code
after the abovementioned, the code will compile -- whether it'll do what is
intended, I've no idea, I'd have to look at the sources to see what
haskellStyle and makeTokenParser actually do (and of course I don't know what
you want to have).
Hope, that's it,
Daniel
Can some one explain this to me? How can I get this code to work?
--- Here is the code ---
module Expressionparser where
import Data.Char
import Text.ParserCombinators.Parsec
import Text.ParserCombinators.Parsec.Expr
import Text.ParserCombinators.Parsec.Token
import Text.ParserCombinators.Parsec.Language
run :: Show a = Parser a - String - IO()
run p input
= case(parse p input) of
Left err - do { putStr parse error at ; print err }
Right x - print x
runLex :: Show a = Parser a - String - IO()
runLex p
= run (do{ whiteSpace lang
; x - p
; eof
; return x
}
)
lang= makeTokenParser
(haskellStyle{ reservedNames = [return,total]})
expr = buildExpressionParser table factor ? expression
table = [ [op * (*) AssocLeft, op / div AssocLeft]
, [op + (+) AssocLeft, op - (-) AssocLeft]
]
where
op s f assoc
= Infix (do{ symbol lang s; return f } ? operator) assoc
factor = parens lang expr
| natural lang
? simple expression
test1 = do{ n - natural lang
; do{ symbol lang +
; m - natural lang
; return (n+m)
}
| return n
}
---
price :: Parser Int -- this is the price in cents
price = lexeme (do{ ds1 - many1 digit
; char '.'
; ds2 - count 2 digit
; return (convert 0 (ds1 ++ ds2))
})
? price
where
convert n [] = n
convert n (d:ds) = convert(10*n + digitToInt d) ds
receipt :: Parser Bool
receipt = do{ ps - many produkt
; p - total
; return (sum ps == p)
}
produkt = do{ symbol return
; p - price
; semi
; return (-p)
}
| do{ identifier
; p - price
; semi
; return p
}
? produkt
total = do{ p - price
; symbol total
; return p
}
--- end code ---
Here are the errors:
___ ___ _
/ _ \ /\ /\/ __(_)
/ /_\// /_/ / / | | GHC Interactive, version 6.2.2, for Haskell
98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/
\/\/ /_/\/|_| Type :? for help.
Loading package base ... linking ... done.
Prelude :l ~/expression-parser.hs
Compiling Expressionparser ( /home/greg//expression-parser.hs,
interpreted )
/home/greg//expression-parser.hs:59:
Variable not in scope: `digitToInt'
Failed, modules loaded: none.
Prelude :r
Compiling Expressionparser ( /home/greg//expression-parser.hs,
interpreted )
/home/greg//expression-parser.hs:51:
Couldn't match
`GenParser tok st a'
against
`CharParser st1 a1 - CharParser st1 a1'
Expected type: GenParser tok st a
Inferred type: CharParser st1 a1 - CharParser st1 a1
Probable cause: `lexeme' is applied to too few arguments in the call
(lexeme (do
ds1 - many1 digit
char '.'
ds2 - count 2 digit
return (convert 0 (ds1 ++ ds2
In the first argument of `(?)', namely
`lexeme (do
ds1 - many1 digit
char '.'
ds2 - count 2 digit
return (convert 0 (ds1 ++ ds2)))'
/home/greg//expression-parser.hs:67:
Couldn't match `GenParser tok st' against `(-) String'
Expected type: GenParser tok st t
Inferred type: String - CharParser st1 String
Probable cause: `symbol'
[Haskell-cafe] Haskell Questions
Hi,
I'm working on a version of Simon Thompson's code from The Craft of Functional
programming to handle polymorhpic data types.
Heres the question Im working on - Ive tried doing the first part, but i would
really apprecate it if someone could let me know if ive implemented it wrong.
Mike
import Hugs.Prelude;
import Monad;
import System;
import Control.Monad.Error;
import Char;
{--
USEFUL AUXILIARY CONSTRUCTS
--}
list2set :: Eq a = [a] - [a]
list2set [] = []
list2set (x:xs)
| x `elem` xs = list2set xs
| otherwise = x : list2set xs
inBrackets :: String - String
inBrackets str = ( ++ str ++ )
inBrackets2 :: String - String - String
inBrackets2 [] s2 = s2
inBrackets2 s1 [] = s1
inBrackets2 s1 s2 = inBrackets (s1 ++ ++ s2)
joinStrings :: String - [String] - String
joinStrings _ [] =
joinStrings _ [s] = s
joinStrings sep (s:ss) = s ++ sep ++ joinStrings sep ss
char2str :: Char - String
char2str x = [x]
dig2int :: Char - Int
dig2int d = fromEnum d - fromEnum '0'
str2int :: String - Int
str2int s = str2intAux (reverse s)
where str2intAux [x]= dig2int x
str2intAux (x:xs) = dig2int x + 10*(str2intAux xs)
{--
PARSING / PATTERN MATCHING
Code based on Thompson, Section 17.5
--}
infixr 5 *
type Parse a b = [a] - [(b,[a])]
-- Don't match anything
matchNone :: Parse a b
matchNone inp = []
-- Add a symbol into the stream and assert match
matchAndAdd :: b - Parse a b
matchAndAdd val inp = [(val,inp)]
-- Match if next input satisfies a given property
matchProperty :: (a - Bool) - Parse a a
matchProperty p (x:xs)
| p x = [(x,xs)]
| otherwise = []
matchProperty _ [] = []
-- Match the next input symbol
matchInput :: Eq a = a - Parse a a
matchInput t = matchProperty (t==)
-- combine the results of two matchs
-- e.g. (matchLP `alt` matchDigit) checks for an LP or a digit
alt :: (Eq a, Eq b) = Parse a b - Parse a b - Parse a b
alt p1 p2 inp = list2set (p1 inp ++ p2 inp)
-- Chain matches together to recognise strings
(*) :: Parse a b - Parse a c - Parse a (b,c)
(*) p1 p2 inp = [((y,z),rem2) | (y,rem1) - p1 inp, (z,rem2) - p2 rem1 ]
-- Build values from matchd strings
build :: Parse a b - (b - c) - Parse a c
build p f inp = [ (f x, rem) | (x, rem) - p inp ]
-- Match a list of symbols all satisfying the same property
matchList :: (Eq a, Eq b) = Parse a b - Parse a [b]
matchList p = (matchAndAdd []) `alt`
((p * matchList p) `build` (uncurry (:)))
-- Match a single symbols satisfying a property
lift :: (Eq a, Eq b) = Parse a b - Parse a [b]
lift p = (p * matchAndAdd []) `build` (uncurry (:))
-- Match a non-empty list of symbols all satifying the same property
matchNEList :: (Eq a, Eq b) = Parse a b - Parse a [b]
matchNEList p = (p * matchList p) `build` (uncurry (:))
-- Match an alphanumeric string of characters
matchAlphaNums :: Parse Char [Char]
matchAlphaNums = matchList matchAlphaNum
-- Match a non-empty string of inputs, one after the other
matchInputs :: Eq a = [a] - Parse a [a]
matchInputs [] = error matchInputs: Empty test string
matchInputs [x] = matchInput x `build` buildMatch1
where buildMatch1 x = [x]
matchInputs (x:xs) = (matchInput x * matchInputs xs) `build` (uncurry (:))
where buildMatch2 (x,y) = [x,y]
{--
PARTICULAR TOKENS OF INTEREST
--}
matchLP = matchInput '('-- left parenthesis
matchRP = matchInput ')'-- right parenthesis
matchCO = matchInput ','-- comma
matchSP = matchInput ' '-- space
matchLB = matchInput '['-- left bracket
matchRB = matchInput ']'-- right bracket
matchPT = matchInput '.'-- point (dot)
matchSQ = matchInput '\'' -- single quote
matchDQ = matchInput ''-- double quote
matchSL = matchInput '\\' -- slash
matchAny = matchProperty (\_ - True)
matchAlphaNum = matchProperty isAlphaNum
matchUpper= matchProperty isUpper
matchLower= matchProperty isLower
matchDigit= matchProperty isDigit
matchWhiteSpace = matchList matchSP
matchArrow = (matchWhiteSpace * matchInputs - * matchWhiteSpace)
`build` buildArrow
where buildArrow _ = -
matchInt = matchNEList matchDigit
matchFloat = (matchInt * matchPT * matchInt) `build` buildFloat
where buildFloat (x,(_,y)) = (x ++ . ++ y)
matchChar = (matchSQ *
((matchInputs \\' ) `alt` ((matchProperty ('\'' /=)) `build`
char2str))
* matchSQ)
`build` buildChar
where buildChar
[Haskell-cafe] a newbie's question
Hi, I'm beginning to study Haskell, For the following a = [1,2,3] b = "there" do x - a y - b return (x , y) Winhugs cannot run it. Gives Syntax error in input (unexpected backslash (lambda)) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] a newbie's question
On Apr 21, 2005, at 3:47 PM, SCOTT J. wrote: Hi, I'm beginning to study Haskell, For the following a = [1,2,3] b = there do x - a y - b return (x , y) Winhugs cannot run it. Gives Syntax error in input (unexpected backslash ( lambda)) Your problem is that you're using monads to grab the contents of a and b, while a and b are not monadic... You probably if you're only just setting out don't want to pay attention to any of the do notation or monadic code. To get the result it looks like you want, all you need to do is this: (a, b) you can then define this as a new constant: c = (a, b) Hope that helps Bob ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] a newbie's question
Thomas Davie wrote: On Apr 21, 2005, at 3:47 PM, SCOTT J. wrote: Hi, I'm beginning to study Haskell, For the following a = [1,2,3] b = there do x - a y - b return (x , y) Winhugs cannot run it. Gives Syntax error in input (unexpected backslash ( lambda)) Your problem is that you're using monads to grab the contents of a and b, while a and b are not monadic... You probably if you're only just setting out don't want to pay attention to any of the do notation or monadic code. To get the result it looks like you want, all you need to do is this: (a, b) you can then define this as a new constant: c = (a, b) Hope that helps Bob On the other hand, perhaps he wanted all possible combinations of values in the lists a and b. Since a list is a monad, this, for example, works fine: a = [1,2,3] b = there abs = do x - a y - b return (x,y) In Hugs: abs == [(1,'t'),(1,'h'),(1,'e'),(1,'r'),(1,'e'),(2,'t'),(2,'h'),(2,'e'),(2,'r'),(2,'e') ,(3,'t'),(3,'h'),(3,'e'),(3,'r'),(3,'e')] -Paul ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] a newbie's question
Hi, I'm trying to investigate the list monad. I
program
instance Monad [] where
xs = f = concat ( map f xs )
return x = [x]
a = [1,2,3]
b = "there"
do { x - a
y -
b
return (x , y) }
And I get the error
Syntax error in input (unexpected backslash
(lambda))
Jan
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Re: [Haskell-cafe] a newbie's question
Thanks for your assistance. I'm using now
Notepad.exe . Before I did it in Wordpad. I use Windows XP. I'm trying to solve
this nasty problem
- Original Message -
From:
SCOTT J.
To: haskell-cafe@haskell.org
Sent: Thursday, April 21, 2005 5:16
PM
Subject: [Haskell-cafe] a newbie's
question
Hi, I'm trying to investigate the list monad. I
program
instance Monad [] where
xs = f = concat ( map f xs )
return x = [x]
a = [1,2,3]
b = "there"
do { x - a
y -
b
return (x , y) }
And I get the error
Syntax error in input (unexpected backslash
(lambda))
Jan
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Re: [Haskell-cafe] a newbie's question
[sorry if you receive this twice; mailing list problems] SCOTT J. wrote: Thanks for your assistance. I'm using now Notepad.exe . Before I did it in Wordpad. I use Windows XP. I'm trying to solve this nasty problem WordPad probably saved your file in RTF rather than TXT. Keep using Notepad for now, but you really should find yourself a decent programmer's editor - I use Emacs, but maybe some Windows people can recommend what they use on that platform. Also, if you want more helpful error messages, use GHC rather than Hugs. HTH. --KW 8-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] a newbie's question
You may want to have a look there : http://www.haskell.org/libraries/#ide It references some tools to develop in haskell ... Pierre Keith Wansbrough a écrit : [sorry if you receive this twice; mailing list problems] SCOTT J. wrote: Thanks for your assistance. I'm using now Notepad.exe . Before I did it in Wordpad. I use Windows XP. I'm trying to solve this nasty problem WordPad probably saved your file in RTF rather than TXT. Keep using Notepad for now, but you really should find yourself a decent programmer's editor - I use Emacs, but maybe some Windows people can recommend what they use on that platform. Also, if you want more helpful error messages, use GHC rather than Hugs. HTH. --KW 8-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Pierre Barbier de Reuille INRA - UMR Cirad/Inra/Cnrs/Univ.MontpellierII AMAP Botanique et Bio-informatique de l'Architecture des Plantes TA40/PSII, Boulevard de la Lironde 34398 MONTPELLIER CEDEX 5, France tel : (33) 4 67 61 65 77fax : (33) 4 67 61 56 68 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] a newbie's question
Well I think one of the best tools to programme on for Windows is UltraEdit, it will give you colors and other stuff (provided you get the correct file for it which is out on the net). Emacs also exists for windows and is not bad, but I don't know if that is the best tool (I sure like it but I hate when you try tabbing and it does it all wrong). Best Regards NooK - Original Message - From: Keith Wansbrough [EMAIL PROTECTED] To: SCOTT J. [EMAIL PROTECTED] Cc: haskell-cafe@haskell.org Sent: Thursday, April 21, 2005 9:13 PM Subject: Re: [Haskell-cafe] a newbie's question [sorry if you receive this twice; mailing list problems] SCOTT J. wrote: Thanks for your assistance. I'm using now Notepad.exe . Before I did it in Wordpad. I use Windows XP. I'm trying to solve this nasty problem WordPad probably saved your file in RTF rather than TXT. Keep using Notepad for now, but you really should find yourself a decent programmer's editor - I use Emacs, but maybe some Windows people can recommend what they use on that platform. Also, if you want more helpful error messages, use GHC rather than Hugs. HTH. --KW 8-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] read with pattern
It's not really clear to me what you're asking. The function read is a method of the typeclass Read, and it has type Read a = String - a. There are a number of instances of the typeclass Read in the standard prelude (http://www.haskell.org/onlinereport/standard-prelude.html) Notably, instance Read Int where ... instance (Read a, Read b) = Read (a,b) where ... instance (Read a) = Read [a] where ... which, taken together, imply that the type [(Int,Int)] is in the typeclass Read, and so there is a suitable implementation of read :: String - [(Int,Int)] If you want to see how that might be implemented (though haskell implementations are allowed to do the same thing in a different way), see the link to the prelude there. hope this helps, - Cale On 4/21/05, Walt Potter [EMAIL PROTECTED] wrote: I'd like to find a reference to reading with patterns such as read::[(Int,Int)] Thanks, Walt ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
