add option to use already installed ghc

[Paczesiowa]

e.g. custom, hacked version of ghc

[rmoorman]

Does this mean that it will be possible to point the hsenv to a directory where a specific ghc version is installed?

I can imagine that sharing different ghc installations between several hsenvs could greatly reduce space/installation overhead in case you have to deal with a lot of applications with different requirements regarding to ghc.

Imagine the following apps app1 -> /usr/local/ghc/ghc-7.0.2 app2 -> /usr/local/ghc/ghc-7.0.2 app2_testing -> /usr/local/ghc/ghc-7.2.2 app3 -> /usr/local/ghc/ghc-7.0.2 old_app -> /usr/local/ghc/ghc-6.10.4

If one could use hsenv to point app1, app2 and app3 to the same ghc installation directory this would already prevent 2 additional downloads + extraction/installation procedures.

In this case would really appreciate this feature!

Keep up the good work.

[drewr]

I could use this too. I would like to install ghc-7.6.1-x86_64-unknown-linux.tar.bz2 to one place and just refer to it as rmoorman describes. I would rather each project not take 1G.