『すごい H 本』こと『すごい Haskell たのしく学ぼう！』をざざっと読んだので、実際に手を動かしてみたい。ということで、開発環境を整える。

Stack

Stack というツールで GHC （コンパイラ）のインストールやコードのビルドができるらしい。

まず Homebrew でインストール。

$ brew install stack

新規プロジェクト hello-world を作る。

$ stack new hello-world
Downloading template "new-template" to create project "hello-world" in hello-world/ ...

The following parameters were needed by the template but not provided: author-name
You can provide them in /Users/mimikakimemo/.stack/config.yaml, like this:
templates:
  params:
    author-name: value
Or you can pass each one as parameters like this:
stack new hello-world new-template -p "author-name:value"


The following parameters were needed by the template but not provided: author-email, author-name, category, copyright, github-username
You can provide them in /Users/mimikakimemo/.stack/config.yaml, like this:
templates:
  params:
    author-email: value
    author-name: value
    category: value
    copyright: value
    github-username: value
Or you can pass each one as parameters like this:
stack new hello-world new-template -p "author-email:value" -p "author-name:value" -p "category:value" -p "copyright:value" -p "github-username:value"

Looking for .cabal or package.yaml files to use to init the project.
Using cabal packages:
- hello-world/

Selecting the best among 15 snapshots...

Selected mirror https://s3.amazonaws.com/hackage.fpcomplete.com/
Downloading timestamp
Downloading snapshot
Downloading mirrors
Cannot update index (no local copy)
Downloading index
Updated package index downloaded
Update complete
Populated index cache.
* Matches lts-13.5

Selected resolver: lts-13.5
Initialising configuration using resolver: lts-13.5
Total number of user packages considered: 1
Writing configuration to file: hello-world/stack.yaml
All done.

途中の Downloading index でやたらと時間がかかってフリーズしたかと思ったが、10分ほどで完了した。

$ cd hello-world
$ tree -a
.
├── .gitignore
├── ChangeLog.md
├── LICENSE
├── README.md
├── Setup.hs
├── app/
│   └── Main.hs
├── hello-world.cabal
├── package.yaml
├── src/
│   └── Lib.hs
├── stack.yaml
└── test/
    └── Spec.hs

stack build で GHC のインストールもしてくれる。

$ stack build
Preparing to install GHC to an isolated location.
This will not interfere with any system-level installation.
Downloaded ghc-8.6.3.
Installed GHC.
[1 of 2] Compiling Main             ( /Users/mimikakimemo/.stack/setup-exe-src/setup-mPHDZzAJ.hs, /Users/mimikakimemo/.stack/setup-exe-src/setup-mPHDZzAJ.o )
[2 of 2] Compiling StackSetupShim   ( /Users/mimikakimemo/.stack/setup-exe-src/setup-shim-mPHDZzAJ.hs, /Users/mimikakimemo/.stack/setup-exe-src/setup-shim-mPHDZzAJ.o )
Linking /Users/mimikakimemo/.stack/setup-exe-cache/x86_64-osx/tmp-Cabal-simple_mPHDZzAJ_2.4.0.1_ghc-8.6.3 ...
Building all executables for `hello-world' once. After a successful build of all of them, only specified executables will be rebuilt.
hello-world-0.1.0.0: configure (lib + exe)
Configuring hello-world-0.1.0.0...
hello-world-0.1.0.0: build (lib + exe)
Preprocessing library for hello-world-0.1.0.0..
Building library for hello-world-0.1.0.0..
[1 of 2] Compiling Lib              ( src/Lib.hs, .stack-work/dist/x86_64-osx/Cabal-2.4.0.1/build/Lib.o )
[2 of 2] Compiling Paths_hello_world ( .stack-work/dist/x86_64-osx/Cabal-2.4.0.1/build/autogen/Paths_hello_world.hs, .stack-work/dist/x86_64-osx/Cabal-2.4.0.1/build/Paths_hello_world.o )
Preprocessing executable 'hello-world-exe' for hello-world-0.1.0.0..
Building executable 'hello-world-exe' for hello-world-0.1.0.0..
[1 of 2] Compiling Main             ( app/Main.hs, .stack-work/dist/x86_64-osx/Cabal-2.4.0.1/build/hello-world-exe/hello-world-exe-tmp/Main.o )
[2 of 2] Compiling Paths_hello_world ( .stack-work/dist/x86_64-osx/Cabal-2.4.0.1/build/hello-world-exe/autogen/Paths_hello_world.hs, .stack-work/dist/x86_64-osx/Cabal-2.4.0.1/build/hello-world-exe/hello-world-exe-tmp/Paths_hello_world.o )
Linking .stack-work/dist/x86_64-osx/Cabal-2.4.0.1/build/hello-world-exe/hello-world-exe ...
hello-world-0.1.0.0: copy/register
Installing library in /Users/mimikakimemo/repos/hello-world/.stack-work/install/x86_64-osx/lts-13.5/8.6.3/lib/x86_64-osx-ghc-8.6.3/hello-world-0.1.0.0-NpaWwN61fJ91LUORGYsB
Installing executable hello-world-exe in /Users/mimikakimemo/repos/hello-world/.stack-work/install/x86_64-osx/lts-13.5/8.6.3/bin
Registering library for hello-world-0.1.0.0..

stack exec <プロジェクト名>-exe で実行できるらしい。

$ stack exec hello-world-exe
someFunc

用意されている app/Main.hs の内容。

module Main where

import Lib

main :: IO ()
main = someFunc

インポートされている src/Lib.hs はこうなっている。

module Lib
    ( someFunc
    ) where

someFunc :: IO ()
someFunc = putStrLn "someFunc"

よって、最終行を someFunc = putStrLn "Hello, world!" に書き換えてビルド・実行すれば、

$ stack build
hello-world-0.1.0.0: unregistering (local file changes: src/Lib.hs)
hello-world-0.1.0.0: build (lib + exe)
Preprocessing library for hello-world-0.1.0.0..
Building library for hello-world-0.1.0.0..
[2 of 2] Compiling Lib              ( src/Lib.hs, .stack-work/dist/x86_64-osx/Cabal-2.4.0.1/build/Lib.o )
Preprocessing executable 'hello-world-exe' for hello-world-0.1.0.0..
Building executable 'hello-world-exe' for hello-world-0.1.0.0..
[1 of 2] Compiling Main             ( app/Main.hs, .stack-work/dist/x86_64-osx/Cabal-2.4.0.1/build/hello-world-exe/hello-world-exe-tmp/Main.o ) [Lib changed]
Linking .stack-work/dist/x86_64-osx/Cabal-2.4.0.1/build/hello-world-exe/hello-world-exe ...
hello-world-0.1.0.0: copy/register
Installing library in /Users/mimikakimemo/repos/hello-world/.stack-work/install/x86_64-osx/lts-13.5/8.6.3/lib/x86_64-osx-ghc-8.6.3/hello-world-0.1.0.0-NpaWwN61fJ91LUORGYsB
Installing executable hello-world-exe in /Users/mimikakimemo/repos/hello-world/.stack-work/install/x86_64-osx/lts-13.5/8.6.3/bin
Registering library for hello-world-0.1.0.0..
$ stack exec hello-world-exe
Hello, world!

Hello, world! と表示される。