Unison 2.48.4 を Mac OS X に Homebrew を用いてインストール

以下でうまくいった．

# Get rid of existing Unison
brew uninstall --force unison

# Checkout version of homebrew with Unison 2.48.4
cd /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core
git checkout 05460e0bf3ae5f1a15ae40315940b2d39dd6ac52 Formula/unison.rb

# Install
brew install --force-bottle unison

# Set homebrew-core back to normal
git checkout master
git reset HEAD .
git checkout -- .

参考リンク