How do I define two types that refer to each other in OCaml?

Question

The code below reports a syntax error message:

type 'a edge = 
  |Empty 
  |End of 'a * 'a vertex * 'a vertex and
type 'a vertex = 
  |Empty
  |Vertex of 'a * 'a edge list;;

How do you define two types that refer to each other?

+3

lkahtz 28 Mar '12 at 1:10

1 answer

Rafe kettler · Accepted Answer · 2012-03-28T01:16:01+0000

The second is type

not syntactically correct:

type 'a edge = 
  |Empty 
  |End of 'a * 'a vertex * 'a vertex
and 'a vertex = 
  |Empty
  |Vertex of 'a * 'a edge list;;