計算機科学のブログ

name:                lesson
version:             0.1.0.0
github:              "githubuser/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/lesson#readme>

dependencies:
- base >= 4.7 && < 5
- split

library:
  source-dirs: src

executables:
  lesson-exe:
    main:                Main.hs
    source-dirs:         app
    ghc-options:
    - -threaded
    - -rtsopts
    - -with-rtsopts=-N
    dependencies:
    - lesson

tests:
  lesson-test:
    main:                Spec.hs
    source-dirs:         test
    ghc-options:
    - -threaded
    - -rtsopts
    - -with-rtsopts=-N
    dependencies:
    - lesson

module Main where

import Lib

main :: IO ()
main = do
  userInput <- getContents
  print $ calc userInput

module Lib where

import Data.List.Split (splitOn)

trim :: String -> String
trim = filter (/= ' ')

addOrMul :: String -> String
addOrMul x
  | length (filter (== '+') x) == 1 = "+"
  | length (filter (== '*') x) == 1 = "*"
  | otherwise = error "Invalid input"

calc :: (Num a, Read a) => String -> a
calc line =
  let op = addOrMul line
      [x, y] = map (read . trim) $ splitOn op line
   in if op == "+"
        then x + y
        else
          if op == "*"
            then x * y
            else error "invalid op"

% stack exec lesson-exe
1+2
3D
% stack exec lesson-exe
1 +  2
3D
% stack exec lesson-exe
2 * 5
10
%