如何在Haskell中编写函数?

好吧,这真的很愚蠢,但我不明白如何在Haskell中编写主do区域之外的函数。我有一个脚本,它读取一个文件,找到该文件中某个单词的位置,然后将结果放入10个箱子中:

{-# LANGUAGE OverloadedStrings #-}
import Data.Text as T
import Data.Text.Internal.Search
import qualified Data.Vector as V
import qualified Data.Text.IO as TIO
import Statistics.Sample.Histogram

main :: IO ()
main = do
  rawText <- TIO.readFile "jane-eyre.asciidoc"
  let locations = indices "morning" rawText
      vec =  V.fromList $ Prelude.map fromIntegral locations
      (_, sizes) = histogram 10 vec
      histSizes = V.toList sizes
  print histSizes

这很好用。但是现在,当我试图把一些东西抽象成函数时,我做不到 rawText 转换为其自身的功能,例如:

{-# LANGUAGE OverloadedStrings #-}
import Data.Text as T
import Data.Text.Internal.Search
import qualified Data.Vector as V
import qualified Data.Text.IO as TIO
import Statistics.Sample.Histogram

rawText = TIO.readFile "jane-eyre.asciidoc"

main :: IO ()
main = do
  let locations = indices "morning" rawText
      vec =  V.fromList $ Prelude.map fromIntegral locations
      (_, sizes) = histogram 10 vec
      histSizes = V.toList sizes
  print histSizes

我得到:

 • Couldn't match expected type ‘Text’ with actual type ‘IO Text’
 • In the second argument of ‘indices’, namely ‘rawText’

下面是我尝试的另一个例子:

{-# LANGUAGE OverloadedStrings #-}
import Data.Text as T
import Data.Text.Internal.Search
import qualified Data.Vector as V
import qualified Data.Text.IO as TIO
import Statistics.Sample.Histogram

hist text = V.toList sizes where
  locations = indices "morning" text
  vec =  V.fromList $ Prelude.map fromIntegral locations
  (_, sizes) = histogram 10 vec

main :: IO ()
main = do
  rawText <- TIO.readFile "jane-eyre.asciidoc"
  histSizes <- hist rawText
  print histSizes

但我得到:

• Couldn't match type ‘[]’ with ‘IO’
  Expected type: IO Integer
    Actual type: [Integer]
• In a stmt of a 'do' block: histSizes <- hist rawText
  In the expression:
    do { rawText <- TIO.readFile "jane-eyre.asciidoc";
         histSizes <- hist rawText;
         print histSizes }
  In an equation for ‘main’:
      main
        = do { rawText <- TIO.readFile "jane-eyre.asciidoc";
               histSizes <- hist rawText;
               print histSizes }