実践Haskell 効率的でステートフルな配列 UArray型を使って効率のよい配列を作成する UArrayを更新する 初期化
入門Haskellプログラミング (Will Kurt(著)、株式会社クイープ(監修、翻訳)、翔泳社)のUNIT7(実践Haskell)、LESSON42(Haskellでの効率的でステートフルな配列)、42.1(UArray型を使って効率のよい配列を作成する)、UArrayを更新する、クイックチェック 42-2の解答を求めてみる。
package.yaml
name: st-lesson
version: 0.1.0.0
github: "githubuser/st-lesson"
license: BSD3
author: "Author name here"
maintainer: "example@example.com"
copyright: "2022 Author name here"
extra-source-files:
- README.md
- ChangeLog.md
# Metadata used when publishing your package
# synopsis: Short description of your package
# category: Web
# To avoid duplicated efforts in documentation and dealing with the
# complications of embedding Haddock markup inside cabal files, it is
# common to point users to the README.md file.
description: Please see the README on GitHub at <https://github.com/githubuser/st-lesson#readme>
dependencies:
- base >= 4.7 && < 5
library:
source-dirs: src
executables:
st-lesson-exe:
main: Main.hs
source-dirs: app
ghc-options:
- -threaded
- -rtsopts
- -with-rtsopts=-N
dependencies:
- st-lesson
- array
tests:
st-lesson-test:
main: Spec.hs
source-dirs: test
ghc-options:
- -threaded
- -rtsopts
- -with-rtsopts=-N
dependencies:
- st-lesson
コード
app/Main.hs
module Main where
import Control.Monad (forM_)
import Data.Array.Unboxed (UArray, array, (!))
-- import Lib ()
beansInBuckets :: UArray Int Int
beansInBuckets = array (0, 3) $ zip [0 .. 3] $ repeat 0
main :: IO ()
main = do
print beansInBuckets
print "forM_"
forM_ [0 .. 3] $ \n -> print $ beansInBuckets ! n
print "mapM_"
mapM_ (\n -> print $ beansInBuckets ! n) [0 .. 3]
入出力結果(Terminal, Zsh)
% stack runghc app/Main.hs
array (0,3) [(0,0),(1,0),(2,0),(3,0)]
"forM_"
0
0
0
0
"mapM_"
0
0
0
0
%