> I've heard fixed-point view, open datatypes and some others, but I'm >> curious where this pattern comes up in literature and what it is called >> there. >> > > Tim Sheard and Emir Pasalic call this technique "two-level types" in their > JFP'04 paper Two-Level Types and Parameterized Modules: > > http://homepage.mac.com/pasalic/p2/papers/JfpPearl.pdf >
Apparently from reading Section 2 of that paper, they would call ExprF non-recursive type the structure operator. I think, by itself, the type ExprF doesn't mean much. It really matters how it's used to determine what you call it. Martijn already mentioned the fixed-point view, but that only makes since in the context of something like Fix: > data ExprF r = Add r r | Sub r r | Mul r r | Div r r | Num Int > newtype Fix f = In (f (Fix f)) > type Expr = Fix ExprF I believe the F suffix that Martijn used typically means functor, and I sometimes call types like this functors (with an optional but obvious instance of Functor). Regards, Sean
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