Haskell+Nix, Monorepo

.gitignore

dist/
dist-*/
result
result-*
cabal.project.local
Setup
*~
*#*

README.org

Fixup (work around gist limitations)

mkdir -p app/src lib/src ; git mv app{_slash_,/}example.cabal ; git mv app{_slash_src_slash_,/src/}Main.hs ; git mv lib{_slash_,/}lib.cabal ; git mv lib{_slash_src_slash_,/src/}MyLib.hs

Commands

Clean full build

nix-build

Dev mode

nix-shell

Then you can build with cabal build app or build the library and then the app separately via cd lib && cabal v1-install && cd ../app && cabal v1-build – with or without --nix=True (or $HOME/.cabal/config containing nix: True).

app_slash_example.cabal

cabal-version:      3.0
name:               example
version:            0.1.0.0

build-type:         Simple

executable example
    main-is:          Main.hs

    build-depends:
          base
        , example-lib
    hs-source-dirs:   src
    default-language: Haskell2010

app_slash_src_slash_Main.hs

module Main where

import MyLib (myFunction)

main = myFunction

cabal.project

packages: */*.cabal

default.nix

{ pkgs ? import <nixpkgs> {} }:
let
  gitignore = pkgs.nix-gitignore.gitignoreSourcePure [ ./.gitignore ];
  lib = pkgs.haskellPackages.callCabal2nix "" (gitignore ./lib) {};
  app = gitignore ./app;
in { lib = lib; app = pkgs.haskellPackages.callCabal2nix "" app { example-lib = lib; }; }

lib_slash_lib.cabal

cabal-version:      3.0
name:               example-lib
version:            0.1.0.0

build-type:         Simple

library
    exposed-modules:
          MyLib

    build-depends:
          base
    hs-source-dirs:   src
    default-language: Haskell2010

lib_slash_src_slash_MyLib.hs

module MyLib (myFunction) where

myFunction = putStrLn "Hello, world!"

shell.nix

{ pkgs ? import <nixpkgs> {} }:
pkgs.haskellPackages.shellFor {
  packages = p: builtins.attrValues (import ./. { inherit pkgs; });
  buildInputs = [
    pkgs.cabal-install
  ];
}