型の紹介 型の基礎 foldl関数、型シグネチャ
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UNIT2(型の紹介)、LESSON 11(型の基礎)、11.5(練習問題)Q11-3の解答を求めてみる。
コード
lesson/app/Main.hs
module Main where
import Lib
( myFoldl,
)
main :: IO ()
main = do
mapM_
print
[ myFoldl (-) 10 [-5 .. 10],
foldl (-) 10 [-5 .. 10]
]
lesson/src/Lib.hs
module Lib
( myFoldl,
)
where
myFoldl :: (a -> b -> a) -> a -> [b] -> a
myFoldl f init [] = init
myFoldl f init (x : xs) = myFoldl f (f init x) xs
入出力結果(Terminal, Zsh)
% stack build
lesson> build (lib + exe)
Preprocessing library for lesson-0.1.0.0..
Building library for lesson-0.1.0.0..
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/7091f650d3dd5d7cbe41c419933d22622a88b13592d474a4616bbcad00d1cf98/9.0.2/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/7091f650d3dd5d7cbe41c419933d22622a88b13592d474a4616bbcad00d1cf98/9.0.2/bin
Registering library for lesson-0.1.0.0..
% stack exec lesson-exe
-30
-30
%