I found 'Learn You a Haskell's' treatment to be very good. After it, you have have some taste for mathematics, is Moggi's paper http://www.disi.unige.it/person/

I found 'Learn You a Haskell's' treatment to be very good. After it, you have have some taste for mathematics, is Moggi's paper http://www.disi.unige.it/person/MoggiE/ftp/ic91.pdf http://www.disi.unige.it/person/MoggiE/ftp/ic91.pdf