[Caml-list] exposing module types

[Caml-list] exposing module types

[Charles Martin]

I obviously have the wrong model of what's going on here:

	% cat foolib.ml
	module Foo = struct
	  module type INTF = sig
	    type 'a fruit = Apple of 'a
	  end
	  module Impl : INTF = struct
	    type 'a fruit = Apple of 'a
	  end
	  type 'a fruit = 'a Impl.fruit
	end
	include Foo
	% ocamlc -a -o foolib.cma foolib.ml

Now, when I try to use foolib in the following way:

	open Foolib

	let apple = Apple 3
	let apple = Foo.Apple 3
	let apple = Foo.Impl.Apple 3

The only one that works is "Foo.Impl.Apple" - the others receive "Unbound constructor" messages.  I hope my intention is clear; in foolib I meant to expose the constructors at the higher levels.  What am I doing wrong?

Thanks,

Charles


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Re: [Caml-list] exposing module types

[Alain Frisch]

On Fri, 8 Feb 2002, Charles Martin wrote:

> I obviously have the wrong model of what's going on here:
>
> 	% cat foolib.ml
> 	module Foo = struct
> 	  module type INTF = sig
> 	    type 'a fruit = Apple of 'a
> 	  end
> 	  module Impl : INTF = struct
> 	    type 'a fruit = Apple of 'a
> 	  end
> 	  type 'a fruit = 'a Impl.fruit
> 	end
> 	include Foo
> 	% ocamlc -a -o foolib.cma foolib.ml


> What am I doing wrong?

The line "type 'a fruit = 'a Impl.fruit" just asserts that the type
'a fruit is the same as 'a Impl.fruit. It does not say what its
value constructors are, though this could be deduced. The solution is to
replace the line with:

type 'a fruit = 'a Impl.fruit = Apple of 'a

(or: include Impl, but that is probably not what you want to do)


-- Alain

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Re: [Caml-list] exposing module types

[Daniel de Rauglaudre]

Hi,

On Fri, Feb 08, 2002 at 01:08:44PM -0800, Charles Martin wrote:

> The only one that works is "Foo.Impl.Apple"

Change the line:
 	  type 'a fruit = 'a Impl.fruit
into:
 	  type 'a fruit = 'a Impl.fruit = Apple of 'a

The type name was visible but not its constructor.

-- 
Daniel de RAUGLAUDRE
daniel.de_rauglaudre@inria.fr
http://cristal.inria.fr/~ddr/
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