Not sure if that's what you need: data NodeF f = Node {name :: String, refs :: [f (NodeF f)]} newtype Const a b = Const a newtype Id a = Id a type NodeS = NodeF (Const String) type Node = NodeF Id Отправлено с iPhone Dec 12, 2010, в 20:54, Florian Weimer написал(а):

Suppose I've got some named objects which reference other objects by name:

...

data NodeS = NodeS {nameS :: String, refsS :: [String]}

Through name resolution, the strings are translated to the actual nodes they denote:

...

data Node = Node {name :: String, refs :: [Node]} resolve :: [NodeS] -> Map String Node

NodeS and Node are quite similar, so they should probably be the same parametrized type. However, if I turn the type of the references into a type parameter, I need the type-level Y combinator to avoid an infinite type, and manipulating nodes turns a bit more tedious because of increased syntactic overhead.

Is there a third choice, beyond manually expanding the type definition or using Y?

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe