関数型プログラミングの基礎 高階関数 filter関数とmap関数、空白、小文字、回文
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 9(高階関数)、9.6(練習問題)Q9-2の解答を求めてみる。
コード
lesson/app/Main.hs
module Main where
import Lib (isPalindrome)
main :: IO ()
main = do
mapM_ print $
isPalindrome
<$> ["A man a plan a canal Panama", "abcde"]
lesson/src/Lib.hs
module Lib
( isPalindrome,
)
where
import Data.Char (isSpace, toLower)
isPalindrome :: String -> Bool
isPalindrome xs =
let text = filter (not . isSpace) $ map toLower xs
in text == reverse text
入出力結果(Terminal, Zsh)
% stack build
lesson-0.1.0.0: unregistering (local file changes: src/Lib.hs)
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..
[1 of 2] Compiling Main [Lib changed]
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/494c7f11ebc566ca0dd51f0cf6ed1f4268c15f68d59cb48ce0d42f2bf991d579/9.0.2/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/494c7f11ebc566ca0dd51f0cf6ed1f4268c15f68d59cb48ce0d42f2bf991d579/9.0.2/bin
Registering library for lesson-0.1.0.0..
% stack exec lesson-exe
True
False
%