I have tranformation functions of the type: > type transformer= a->Maybe b I have defined the operator ++> as > mbX ++> f = maybe Nothing f mbX So that I can represent a set of transformations on an object that either succeed or fail. e.g. > validObject = lookup "foo" ++> -- lookup foo in hashtable > (decrypt key) ++> -- decrypt string if possible > (acceptIfNormal.read) --check sanity of > --deserialized objet Note that each action could result in Nothing and return Nothing or it returns a value that is passed on to the next command. I have two questions here: 1. What is the standard name for the ++> opertor. Because it is very similar to >>= and the this pattern must be very common, I assume that there is a more standard name for the ++> operator that is in a library or prelude. (I don't want to add obscure opertors that know one recognizes to my code) 2. Initially, I defined ++> as > x ++> f = x ++ f x But that seemed to require that x and (f x) be of the same type. Would existential types allow x and (f x) to be of different type? How would you define ++ for type Maybe to accomplish that? -Alex- ___________________________________________________________________ S. Alexander Jacobson i2x Media 1-212-697-0184 voice 1-212-697-1427 fax
