F# Circular Type Definition Loop

Question

I want to have a type A which has a property which is an instance of type B. And type B has a property of an instance of type A. The problem is, F# reads the source files in order. So if I define type A first, then it won't recognize type B. And if I define type B first, I can't make it have an instance of A. Is there a way around this, or is this just bad design on my part?

`type a() ... and b() ` - almost certainly a duplicate of something — John Palmer, Jun 19 '15 at 13:05
Not exactly an answer to your question but this article gives a nice overview of the issue: http://fsharpforfunandprofit.com/posts/cyclic-dependencies/ — PiotrWolkowski, Jun 19 '15 at 13:13

score 8 · Accepted Answer · answered Jun 19 '15 at 13:07

8

You can a define mutually recursive type if they are in the same file like this

type Chicken =
   | Eggs of Egg list
and Egg =
   | Chickens of Chicken list

answered Jun 19 '15 at 13:07

Daniel Slater

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F# Circular Type Definition Loop

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