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 accum関数
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 42-3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 Data.Array.Unboxed
-- import Lib ()
beansInBuckets :: UArray Int Int
beansInBuckets = array (0, 3) $ zip [0 .. 3] $ [2, 7, 2, 8]
updatedBiB = accum (*) beansInBuckets $ zip [0..3] $ repeat 3
main :: IO ()
main = do
mapM_ print
[beansInBuckets,
updatedBiB]
入出力結果(Terminal, Zsh)
% stack runghc app/Main.hs
array (0,3) [(0,2),(1,7),(2,2),(3,8)]
array (0,3) [(0,6),(1,21),(2,6),(3,24)]
%