Difficult to use custom database path for search

(Haskell + hoogle newbie here, please be aware!)

What I wanted:
Download hoogle database for offline use.

What I tried:
Generate database (worked fine, the --datadir option was documented in hoogle data --help):

hoogle data --datadir=$HOME/.hoogle-datadir

Search, using my --datadir (didn't work):

$ hoogle --datadir=$HOME/.hoogle-datadir map
Unknown flag: --datadir

Uh oh, why doesn't it understand --datadir now?

I installed hoogle with the nix package manager, so the installation directory is read-only. I need the custom datadir not just for having multiple databases on my system, but it is the only way to use the program:

$ hoogle data
hoogle: /nix/store/mdvxcf25a0gr6lrbnwv6waisanrhbc81-haskell-hoogle-4.2.41/share/x86_64-linux-ghc-7.10.1/hoogle-4.2.41/databases: createDirectory: permission denied (Read-only file system)

Workaround
Because I couldn't find a way to tell hoogle to use --datadir= for searching, I made a wrapper script that uses cd $datadir && exec hoogle ....

Solution
What I think should have been needed to be done. Configure datadir with one of these options:

$ echo "datadir=$HOME/.hoogle-datadir" >> ~/.hooglerc
$ export HOOGLE_DATADIR=$HOME/.hoogle-datadir
(or all commands that use the database/datadir accept the --datadir=... option)

Now search:

$ hoogle data
$ hoogle <search>

Start by comparing the option handling for hoogle data --datadir with the search invocation, then check the configuration examples in the issue. The change is complete when a database in a custom datadir can be generated and searched without changing directories, using either the documented configuration or a supported command-line option.