I recently set up Agda on OS X 10.9, and noticed that there was a very minor difference in step 3, as compared to the description on the official page on installing Agda on OSX. The steps are as follows:

1) Install the Haskell Platform

2) Type “cabal update” in the terminal

3) Update the PATH variable in the file .bash_profile, which is to be found in your home directory. If not, create it. Editing .profile had no effect on my OS X installation. Paste this line into bash_profile:

export PATH="$HOME/Library/Haskell/bin:$PATH"

4) Type “cabal install Agda” in the terminal

5) Install Aquamacs

6) Type “agda-mode setup” in the terminal. Note that this step will fail if you didn’t add Haskell to your PATH in .bash_profile.

7) Restart Aquamacs

Now load an .agda file to ensure that the menu ‘Agda’ appears in the menu bar of Aquamacs. Afterwards, you can proceed installing the Agda standard library.