Just find out

The installation failed at the end

It failed because I did not install the command line tools in XCode. After installing the tool, the gem command ran fine.

erlware-mode is deprecated.

Use erlang-mode in erlang distribution instead

Currently the version of erlang in homebrew is defaulted to version R15B03-1 even though a more recent version, R16B, is available.

To install R16B, it is what I did:

Find out the current emac.d location

C-H v init-user-file <RET>