[Haskell-cafe] What's this pattern called?

[Martijn van Steenbergen]

Bonjour café,

> data ExprF r
>   =  Add  r  r
>   |  Sub  r  r
>   |  Mul  r  r
>   |  Div  r  r
>   |  Num  Int

This is a well-known pattern that for example allows nice notation of 
morphisms. But what is it called? 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.

Thanks,

Martijn.