Use untap

brew untap sethdeckard/proj

They provide an official uninstall script you can download and run:

ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/uninstall)"

Homebrew once recommended an older script, also linked in their FAQ.

Here is a copy of the old script, for historical purposes:

cd `brew --prefix`
git checkout master
git ls-files -z | pbcopy
rm -rf Cellar
bin/brew prune
pbpaste | xargs -0 rm
rm -r Library/Homebrew Library/Aliases Library/Formula Library/Contributions 
test -d Library/LinkedKegs && rm -r Library/LinkedKegs
rmdir -p bin Library share/man/man1 2> /dev/null
rm -rf .git
rm -rf ~/Library/Caches/Homebrew
rm -rf ~/Library/Logs/Homebrew
rm -rf /Library/Caches/Homebrew

This should also revert your /usr/local folder to its pre-Homebrew days. See the Homebrew installation wiki for more information.

Note: You may also need to remove ~/.homebrew as well. If you happen to have ~/.rvm, then you should delete ~/.rvm/bin/brew. If any of your brew package had brew services that are running, you should turn them off. If any packages installed their own libraries (like Python's pip) you'll have to uninstall those manually.

Taps are sources of formulae. A formula is a file that describes how to install software. The main tap is homebrew/core but anybody can create one. Taps are managed with the brew tap and brew untap commands.

When Homebrew tells you it’s "searching local taps", it means it’s looking for an ocaml formula in one of the taps you have locally. If one of the formula it finds is installed locally, it’ll show it in bold with a little checkmark next to it:

# OCaml is installed
$ brew search ocaml
==> Searching local taps...
ocaml ✔  ocamlbuild  ocamlsdl

# Ocaml is NOT installed
$ brew search ocaml
==> Searching local taps...
ocaml  ocamlbuild  ocamlsdl

As you can see in your case, you don’t get that checkmark so Ocaml is not installed. You can be sure by typing brew info ocaml:

$ brew info ocaml
ocaml: stable 4.05.0 (bottled), HEAD
General purpose programming language in the ML family
https://ocaml.org/
Not installed  <--------- look here
...

As for taps you can list those you have locally using brew tap:

$ brew tap
homebrew/core
homebrew/services
homebrew/fuse
homebrew/nginx
homebrew/php
...

The exact output may vary but you’ll always have at least homebrew/core.

To add a new tap, use brew tap <tap>:

 brew tap homebrew/science

To remove a tap, use brew untap <tap>:

 brew untap homebrew/science

Note you can’t remove homebrew/core.