計算機科学のブログ

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

module Main where

import Control.Monad (forM_, when)
import Data.Array.ST (readArray, runSTUArray, thaw, writeArray)
import Data.Array.Unboxed (IArray (bounds), UArray, array)

-- import Lib ()

replaceZeros :: UArray Int Int -> UArray Int Int
replaceZeros a = runSTUArray $ do
  stArray <- thaw a
  let end = (snd . bounds) a
  forM_ [0 .. end] $ \i -> do
    val <- readArray stArray i
    when (val == 0) $ do
      writeArray stArray i (-1)
  return stArray

a :: UArray Int Int
a = array (0, 9) $ zip [0 .. 9] [0, 5, 1, 0, 0, 4, 0, 2, 0, 3]

main :: IO ()
main = do
  mapM_ print [a, replaceZeros a]

% stack runghc app/Main.hs
array (0,9) [(0,0),(1,5),(2,1),(3,0),(4,0),(5,4),(6,0),(7,2),(8,0),(9,3)]
array (0,9) [(0,-1),(1,5),(2,1),(3,-1),(4,-1),(5,4),(6,-1),(7,2),(8,-1),(9,3)]
%