関数型プログラミングの基礎 再帰関数の記述 reverseを実装、パターンマッチ、引数
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UNIT1(関数型プログラミングの基礎)、LESSON 8(再帰関数の記述)、8.5(練習問題)Q8-1の解答を求めてみる。
コード
lesson/app/Main.hs
module Main where
import Lib (myReverse)
main :: IO ()
main = do
mapM_ print $
myReverse
<$> [[], [1], [1, 2], [1 .. 5]]
lesson/src/Lib.hs
module Lib
( myReverse,
)
where
myReverse [] = []
myReverse (x:xs) = myReverse xs ++ [x]
入出力結果(Terminal, Zsh)
% stack build
lesson-0.1.0.0: unregistering (local file changes: app/Main.hs src/Lib.hs)
lesson> configure (lib + exe)
Configuring lesson-0.1.0.0...
lesson> build (lib + exe)
Preprocessing library for lesson-0.1.0.0..
Building library for lesson-0.1.0.0..
[2 of 2] Compiling Lib
Preprocessing executable 'lesson-exe' for lesson-0.1.0.0..
Building executable 'lesson-exe' for lesson-0.1.0.0..
[2 of 2] Compiling Main
Linking .stack-work/dist/x86_64-osx/Cabal-3.4.1.0/build/lesson-exe/lesson-exe ...
lesson> copy/register
Installing library in /Users/…/lesson/.stack-work/install/x86_64-osx/b6e8c918185b27e9dcbc52db0653ed10d7a4ac8a88584523c7314e6b50554430/9.0.2/lib/x86_64-osx-ghc-9.0.2/lesson-0.1.0.0-CIOIkpTgcfQI9akDJnwnSd
Installing executable lesson-exe in /Users/…/lesson/.stack-work/install/x86_64-osx/b6e8c918185b27e9dcbc52db0653ed10d7a4ac8a88584523c7314e6b50554430/9.0.2/bin
Registering library for lesson-0.1.0.0..
% stack exec lesson-exe
[]
[1]
[2,1]
[5,4,3,2,1]
%