haskell 中非记录数据构造函数的术语

Question

data A b c = B | C b | H { b :: b, c :: c }

AFAIK, B is called nullary constructor C is called unary constructor, while H is called record.

But what is the term for arbitrary-arity constructors including both B and C ? Is there something better than non-record constructors?

Answer 1

I'm not sure they deserve a special name. A record constructor is basically just a non-record constructor with some automatically defined accessor functions and convenient syntactic support. In your example above, I would consider H a binary constructor or a constructor of arity 2, since I can construct and destruct it like any other binary constructor:

let H a b = H (1+1) (2+2) in (a,b)

For what it's worth, the Haskell98 report just calls them "constructors with field labels" and "constructors without field labels" and makes it pretty clear that even with field labels they are still "data constructors of arity k".