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Cyclic dependencies between data types
f#

Hi,
I'm new to F# and to this forum (so please have patience). I have

a question about how to deal with cyclic dependencies between data type

definitions. Basically I'd like to do something like the following:

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type FooList =
   abstract ToFooList : List<Foo>

type Foo =
   {foo : String}
   interface FooList with
      member f.ToFooList = [f]

where I want to be able to define different data types all implementing the 'FooList' interface. Now, the problem is that I cant define 'Foo' before 'FooList' or the other way around.

However, I found a way of dealing with this particular problem

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type ToList<'c> =
    abstract ToList : List<'c>
      
type Foo =
   {foo : String}
   interface ToList<Foo> with
      member f.ToList = [f]

but I still wonder if there is a simpler general solution.

Thanks,
Joel

.

You're right to wonder.

In the first code, change the second occurence of "type" to "and" and all is well. Similar to "let rec ... and ..."

By on 10/16/2008 1:39 PM ()

Great, thanks a lot! So, this is obviously also the way of dealing with mutually recursive functions.

Btw, what are motives of the requirement of adding things to scope "top down"? Is it simply inherited from Ocaml, are there any implementation related motives or just an idiom that people agree on? I can definitly see why it is required for "script" files.

Since I'm coming from the Haskell world and I'm actually more used to declaring things the opposite order, i.e. top-level functions at the top of the file and helper functions below.

By on 10/16/2008 2:41 PM ()

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