Re: [Haskell-cafe] Basic Parsec float & integer parsing question

5 Jul 2013

      Token parsers are specific to different languages.  Afterall, haskell
parses floats differently than C, which is different from java
(probably).  In order to use it in your code you have to tell it that,
like so:

haskelldef = makeTokenParser haskellDef

header :: Parser LabelFile
header = do
  string headTS1
  start <- fmap double2Float $ float haskelldef
  string "\nxmax = "
  end <- fmap double2Float $ float haskelldef
  string "\ntiers? <exists>\nsize = "
  integer haskelldef
  char '\n'
  return $ LabelFile start end

You'll need to import GHC.Float (double2Float) to get those parsed
values as floats.

On Fri, Jul 5, 2013 at 12:42 PM, Fredrik Karlsson  wrote:
...
Dear list,
Sorry for asking a simple parsec question, but both Parsec and Haskell is
new to me, so please be gentle :-)
I have this code:
------------------------------------------------------------------------------------------------
import Text.ParserCombinators.Parsec
import Text.Parsec.Token
import Text.ParserCombinators.Parsec.Char
data VariableLine = VariableLine String String deriving Show
data TierType = IntervalTier | PointTier deriving Show
data Tier = Tier TierType String Float Float Integer
data Label = Interval Float Float String
data LabelFile = LabelFile Float Float
symbol :: Parser Char
symbol = oneOf "!#$%&|*+-/:<=>?@^_~"
testString = "intervals [1]:\n    xmin = 0 \n    xmax = 0.028199999999999992
\n    text = \"\""
headTS1 = "File type = \"ooTextFile\"\nObject class = \"TextGrid\"\n\nxmin
="
header :: Parser LabelFile
header = do
headTS1
start <- float
string "\nxmax = "
end <- float
string "\ntiers? <exists>\nsize = "
integer
char '\n'
return $ LabelFile start end
------------------------------------------------------------------------------------------------
Loading it into ghci I get :
Prelude> :l parsectest.hs
[1 of 1] Compiling Main             ( parsectest.hs, interpreted )
parsectest.hs:21:9:
    Couldn't match type `[]'
                  with `Text.Parsec.Prim.ParsecT
                          String () Data.Functor.Identity.Identity'
    Expected type: Text.Parsec.Prim.ParsecT
                     String () Data.Functor.Identity.Identity Char
      Actual type: [Char]
    In a stmt of a 'do' block: headTS1
    In the expression:
      do { headTS1;
           start <- float;
           string
             "\
             \xmax = ";
           end <- float;
           .... }
    In an equation for `header':
        header
          = do { headTS1;
                 start <- float;
                 string
                   "\
                   \xmax = ";
                 .... }
parsectest.hs:22:18:
    Couldn't match expected type `Text.Parsec.Prim.ParsecT
                                    String () Data.Functor.Identity.Identity
Float'
                with actual type `GenTokenParser s0 u0 m0
                                  -> Text.Parsec.Prim.ParsecT s0 u0 m0
Double'
    In a stmt of a 'do' block: start <- float
    In the expression:
      do { headTS1;
           start <- float;
           string
             "\
             \xmax = ";
           end <- float;
           .... }
    In an equation for `header':
        header
          = do { headTS1;
                 start <- float;
                 string
                   "\
                   \xmax = ";
                 .... }
parsectest.hs:24:16:
    Couldn't match expected type `Text.Parsec.Prim.ParsecT
                                    String () Data.Functor.Identity.Identity
Float'
                with actual type `GenTokenParser s1 u1 m1
                                  -> Text.Parsec.Prim.ParsecT s1 u1 m1
Double'
    In a stmt of a 'do' block: end <- float
    In the expression:
      do { headTS1;
           start <- float;
           string
             "\
             \xmax = ";
           end <- float;
           .... }
    In an equation for `header':
        header
          = do { headTS1;
                 start <- float;
                 string
                   "\
                   \xmax = ";
                 .... }
parsectest.hs:26:9:
    Couldn't match expected type `Text.Parsec.Prim.ParsecT
                                    String () Data.Functor.Identity.Identity
a0'
                with actual type `GenTokenParser s2 u2 m2
                                  -> Text.Parsec.Prim.ParsecT s2 u2 m2
Integer'
    In a stmt of a 'do' block: integer
    In the expression:
      do { headTS1;
           start <- float;
           string
             "\
             \xmax = ";
           end <- float;
           .... }
    In an equation for `header':
        header
          = do { headTS1;
                 start <- float;
                 string
                   "\
                   \xmax = ";
                 .... }
Failed, modules loaded: none.
I'm sure I'm doing something really stupid here, but I need help to get
through this problem. I've used the predefined "letter" parser at other
places in the code, so I can't understand why "float" and "integer" does not
work.
/Fredrik
--
"Life is like a trumpet - if you don't put anything into it, you don't get
anything out of it."
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Re: [Haskell-cafe] Basic Parsec float & integer parsing question

David McBride