Following works for me:
$ brew install readline
$ cabal install readline --configure-option=--with-readline-includes=/usr/local/Cellar/readline/6.2.1/include --configure-option=--with-readline-libraries=/usr/local/Cellar/readline/6.2.1/lib
Following works for me:
$ brew install readline
$ cabal install readline --configure-option=--with-readline-includes=/usr/local/Cellar/readline/6.2.1/include --configure-option=--with-readline-libraries=/usr/local/Cellar/readline/6.2.1/lib