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parsinghaskellparsec
Gabo
Gabo

Reputation: 35

How to Parse a floating number in Haskell (Parsec.Combinator)

I'm trying to parse a string in haskell using Parsec.Combinator library. But I can't find how to parse a floating value. My function only reads integer (with digit, but digit only parses a integer value).

parsePoint :: Parser Point
parsePoint = do
              string "Point"
              x <- many1 digit
              char ','
              y <- many1 digit
              return $ (Point (read x) (read y))

I searched for Text.Parsec.Number library but didn't find examples to how to use.

thanks for reading

Upvotes: 2

Views: 376

Answers (1)

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 477533

There are several Parsers that can parse floats, for example floating :: (Floating f, Stream s m Char) => ParsecT s u m f. The Parser is just an alias for a special case of Parsec, depending on which module you use. For example type Parser = Parsec Text ().

If your Point thus accepts for example two Floats, you can use the parsec3-numbers package and work with:

import Text.Parsec.Char(char, string)
import Text.Parsec.Number(floating)
import Text.Parsec.Text(Parser)

data Point = Point Float Float

parsePoint :: Parser Point
parsePoint = do
              string "Point "
              x <- floating
              char ','
              y <- floating
              return (Point x y)

This then can parse, in this case a string "Point 3.14,2.718"

Upvotes: 4

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