Hi libraries@, (Let me know if there's a better place for Cabal questions. This list is linked from https://www.haskell.org/cabal/ as a place to ask questions.) I have a project with lots of modules, and lots of executables that use those modules. How should I structure my .cabal file if I want cabal to only build the common modules once? I have found I can do it as follows, but I am wondering if there's a way to do it without step 1: 1. Create a "library_src" directory with the source for all the shared modules. Put the source files for the executables somewhere else. 2. Create a .cabal file with one "library" stanza with "hs-source-dirs: library_source", and several executable stanzas. If I leave out step 1 and put all the source files in the same place, then the compiler builds them separately for each executable, and I get a "missing-home-modules" warning. Is it just a fact of life that I need to separate my source into separate directories if I want this to work properly? Here's a small example, with four files, where I left out step 1 (i.e. put everything in the same directory). It does not behave the way I want it to: it builds the Library module three times if I run "cabal v2-build" and "cabal v2-test", and it shows the "missing-home-modules" warning. It also still builds if I remove "mhm" from build-depends of the executable and test-suite; I'd rather it failed to build if I did that. mhm.cabal: cabal-version: 2.2 name: mhm version: 0 library exposed-modules: Library default-language: Haskell2010 build-depends: base >=4.12 && <4.13 executable e main-is: e.hs build-depends: mhm, base >=4.12 && <4.13 default-language: Haskell2010 test-suite t type: exitcode-stdio-1.0 main-is: t.hs build-depends: mhm, base >=4.12 && <4.13 default-language: Haskell2010 Library.hs: module Library where n :: Int n = 5 e.hs: module Main where import Library main = print n t.hs: module Main where import Library main = print n