On Tue, May 25, 2010 at 07:59:24PM +0100, Stephen Tetley wrote: > Hi Eugeny > > Its not that GHC thinks you're doing something weird, but that there > is no relation between the type parameters in the Storage class. You > could use either functional dependencies or type families to introduce > a relation / relations, but personally I would look at doing something > simpler - for instance why do you need a map type that is polymorphic > on shape?
Currently I am creating set of objects from name-value pairs, and I decided to use Map for keeping relations between an object id and record with the id. So I will be able to parse the parameter like param_1_propname=value then take the object with ID=1 from Map, and update it's property 'propname' with value, and put it back into the Map. But I faced several cases when a set of name-value pairs describes 2 or even more kinds of objects. And I want to be able to parse them all at one pass, so I would need 2 or more maps. And I simply tried to generalize the solution. Probably I should think in different way. May be a chain of Writer monads or something similar. -- Eugene Dzhurinsky
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