CODEWITHSUNDEEP
haskellsyntax
amindfv
amindfv

Reputation: 8448

Parsing from openFile contents

This seems so simple, but for some reason I'm confusing myself. The "thing" line is giving me the error.
The parsing functions are correct (stolen from RWH). I just have a type error.

Thanks!

import Text.ParserCombinators.Parsec
import System.IO

main = do 
   csv_cont <- openFile "aCSV.txt" ReadMode
   csv_cont1 <- hGetContents csv_cont
   thing <- parseCSV csv_cont1
   return () 


csvFile = endBy line eol
line = sepBy cell (char ',')
cell = many (noneOf ",\n")
eol = char '\n'

parseCSV :: String -> Either ParseError [[String]]
parseCSV input = parse csvFile "(unknown)" input

Upvotes: 1

Views: 146

Answers (1)

Don Stewart
Don Stewart

Reputation: 137947

parseCSV is a pure function (note, no IO in the type). So you don't use "do notation" to bind its result. Instead, just regular let is appropriate:

import Text.ParserCombinators.Parsec
import System.IO

main = do
   h <- openFile "aCSV.txt" ReadMode
   s <- hGetContents h
   let thing = parseCSV s
   print thing


csvFile = endBy line eol
line    = sepBy cell (char ',')
cell    = many (noneOf ",\n")
eol     = char '\n'

parseCSV :: String -> Either ParseError [[String]]
parseCSV s = parse csvFile "(unknown)" s

Here, with more idiomatic naming and identation.

Upvotes: 3

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