It matters whether in the signature of a module that is produced by the
functor, the type of the key is still the same as the type of the key
parameter. If it is not, then debugger cannot know, whether the output type
is a key or not. Probably, if you add a sharing constraint between the
functor parameter signature and the resulting module signature the debugger
with capture it. Especially, if this would be an erasing signature
(although it is not always possible), e.g.,

module M = sig type key type t end
module Make(Key : T) : M with type key = Key.t


or

module Make(Key : T) : M with type key := Key.t



If these approaches do not work for you, then you can define a printer
yourself in a separate module (that is loaded with `load_printer` command).
In this printer you may apply a functor,
and since functors are applicative in OCaml the debugger might be clever
enough to pick this printer. It is not guaranteed, though, as the debugger
is using lots of heuristics, and sometimes, they do fail.


Best wishes,
Ivan



On Thu, Feb 23, 2017 at 11:49 AM, Tom Ridge <tom.j.ridge+list@googlemail.com
> wrote:

> Regarding `#install_printer`, can you explain more? The type
> "Key_value_types.key" is equal to string (in this particular case).
> However, this type is produced via module application, and so I cannot
> construct a printer that can print values of type "Key_value_types.key"
> before program execution (which seems to be required for #install_printer).
>
> Somehow I seem to want to tell ocamldebug that Key_value_types.key is in
> fact equal to string. Or alternatively coerce kra (using Obj.magic) to
> string type so that it can easily be printed by ocamldebug?
>
>
>
> On 23 February 2017 at 16:31, Ivan Gotovchits <ivg@ieee.org> wrote:
>
>> Probably it is an abstract type, that is represented as string. In any
>> case you can use the `#install_printer` directive to enable printing any
>> type. The argument
>> is a function of type `t -> Format.formatter -> unit`, where `t` is a
>> name of your type.
>>
>> On Thu, Feb 23, 2017 at 11:24 AM, Tom Ridge <
>> tom.j.ridge+list@googlemail.com> wrote:
>>
>>> Dear All,
>>>
>>> I am debugging some code. For various reasons I have started to use
>>> ocamldebug rather than printf.
>>>
>>> I should say that ocamldebug is excellent. Really excellent. Especially
>>> the "backwards" stepping.
>>>
>>> However, sometimes I want to see the value of a particular variable. I
>>> can use the "p" (print) command as:
>>>
>>> (ocd) p kra
>>> kra: Key_value_types.key = <abstr>
>>>
>>> The problem is that I know that kra is a string. But ocamldebug only
>>> shows <abstr>.
>>>
>>> Admittedly the code is functorized. But I have a feeling I should be
>>> able to tweak something to get ocamldebug to print the value of kra.
>>>
>>> Any ideas?
>>>
>>> T
>>>
>>
>>
>