A Taste of Haskell

Getting Started with Stack

Stack - The Haskell Tool Stack

Cross-platform tool for developing Haskell projects
Installs GHC (Glasgow Haskell Compiler)
Downloads and installs package dependencies
Isolated environments for each project
Commands for building, testing, benchmarking, etc.

Installing Stack

On Linux, MacOs, run from a terminal


curl -sSL https://get.haskellstack.org/ | sh


wget -qO- https://get.haskellstack.org/ | sh

On Windows, download and run installer

Full instructions on https://docs.haskellstack.org

Hello World!

Type the code in a file helloworld.hs


main = putStrLn "Hello, Haskell world!"

Compile and execute it with


> stack ghc helloworld.hs
[1 of 1] Compiling Main         ( helloworld.hs, helloworld.o )
Linking helloworld ...

> ./helloworld
Hello, Haskell world!

Interactive Haskell

Start an interactive session (REPL)


> stack ghci
Configuring GHCi with the following packages:
GHCi, version 8.2.2: http://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from ...
Prelude>

Load your Haskell program and call its main function


Prelude> :load helloworld.hs
[1 of 1] Compiling Main         ( helloworld.hs, interpreted )
Ok, modules loaded: Main.

*Main> main
Hello, Haskell world!

Using GHCi

Create functions and evaluate Haskell expressions


Prelude> 2 + 3 * (4 ^ 5)
3074
Prelude> 1 < 2
True
Prelude> factorial 0 = 1; factorial n = n * factorial (n - 1)
Prelude> factorial 50
30414093201713378043612608166064768844377641568960512000000000000

Multiline Input


Prelude> :{
Prelude| sumList [] = 0
Prelude| sumList (x:xs) = x + sumList xs
Prelude| :}
Prelude> sumList []
0
Prelude> sumList [1,2,3]
6
Prelude> sumList [1..10000]
50005000

Basic GHCi Commands


:load <file> or :l <file> - load Haskell module
:reload or :r             - reload Haskell module
:cd <dir>                 - change directory
:! <cmd>                  - execute shell command
:help or :?               - list available commands
:quit or :q               - quit GHCi