project-template

Template for a Haskell project.

Prerequisites

This project relies on the Haskell Stack tool.

It is recommended to get Stack with batteries included by installing Haskell Platform.

Build

To build this project simply run

stack build

This will install all dependencies, including a proper version of GHC (which should be there already if you have Haskell Platform 8.6.5).

Run

This project has one executable that you can run with

stack exec my-project-exe

During development it is recommended a combination of build and exec:

stack build && stack exec my-project-exe

Alternatively, you can run

stack build file-watch

For continuous builds in the background.

Interpreter

You can run GHCi (GHC interpreter) for the whole project with

stack ghci

or

stack repl

During development it might be beneficial to work using an interpreter for quick reloads, interacting with various parts of code and trying out things.

Note that you can run executable from GHCi by invoking main.

GHCi commands

There are some useful commands in GHCi that might help you with the development process:

• :t or :type — show the type of an expression:

>>> :t map (+1)
map (+1) :: Num b => [b] -> [b]

• :l or :load — load file or module:

>>> :load src/MyProject.hs
[1 of 1] Compiling MyProject        ( src/MyProject.hs, interpreted )
Ok, one module loaded.

• :set and :unset — turn an option on/off:

>>> :set -XOverloadedStrings
>>> :set -Wall -fno-warn-type-defaults

ghcid

For faster feedback from the compiler it is recommended to use ghcid (GHCi deamon).

Install ghcid with stack:

stack install ghcid

Now you can run ghcid with Stack using

ghcid -c "stack repl"

This will run GHCi with the entire project loaded and will quickly reload all modules when you modify them to tell you if you have any errors or warnings.

Note: you can also run ghcid without parameters and it will detect Stack project, but you'll have to use system-wide .ghci. See ndmitchell/ghcid#72 for more details.

Here's a sample development enviroment with a text editor (left), ghcid (top right) and stack repl (bottom right):