Also the original paper by Phil Wadler - it is very readable: http://homepages.inf.ed.ac.uk/wadler/papers/marktoberdorf/baastad.pdf http://homepages.inf.ed.ac.u

Also the original paper by Phil Wadler - it is very readable: http://homepages.inf.ed.ac.uk/wadler/papers/marktoberdorf/baastad.pdf http://homepages.inf.ed.ac.uk/wadler/papers/marktoberdorf/ba...