$ cabal new-build
Build profile: -w ghc-8.6.5 -O1
In order, the following will be built (use -v for more details):
 - wordnumber-0.1.0.0 (lib) (first run)
 - wordnumber-0.1.0.0 (exe:wordnumber) (first run)
Preprocessing library for wordnumber-0.1.0.0..
Building library for wordnumber-0.1.0.0..
cabal: The program 'ar' is required but it could not be found.

cabal: Failed to build wordnumber-0.1.0.0 (which is required by exe:wordnumber
from wordnumber-0.1.0.0).