I try to use

In this case, it seems extra-1.7.10.

2. *.cabal file -> build-depends: extra >=1.7.10 (among other libs)

3. $ cabal install extra

Error:

cabal: Cannot build the executables in the package extra because it does not contain any executables. Check the .cabal file for the package and make sure that it properly declares the components that you expect.

Well, I did for sure.

4. cabal install extra --lib

Finally works, but the documentation never said this.

Am I correct? ` Is this the only method? or any other smarter way?