Re: why do i have to repeat so much here?

nice trick, thanks!

martin


On Mon, Aug 18, 2014 at 11:28 PM, Philippe Veber [email protected]
[ocaml_beginners] <[email protected]> wrote:

>
>
> Hi Martin,
>
> A frequently used trick is to define your module type in an ml file to
> avoid one repetition:
>
> environment_sig.ml:
>
>
> module type ENV = sig
>   type dict
>
>   type env = {
>     dict : dict;
>     op : Types.uop
>   }
> end
>
> environment.mli:
>
> module Make (Dict : sig type t end) : Environment_sig.ENV with type dict =
> Dict.t
>
>
> environment.ml:
>
>
> module Make (Dict : sig type t end) = struct
>   type dict = Dict.t
>
>   type env = {
>     dict : dict;
>     op : Types.uop
>   }
> end
>
> Cheers,
>   Philippe
>
>
>
>
> 2014-08-19 8:22 GMT+02:00 Martin DeMello [email protected]
> [ocaml_beginners] <[email protected]>:
>
>
>>
>> interesting thread. i usually don't mind repeating myself in the .mli
>> file - i think what is annoying me the most here is that i don't really
>> have an "implementation"; all i want to do is define a single record type
>> with a type parameter. i know i could delete the .mli file and have
>> everything work, but that feels wrong when theoretically i want to delete
>> the .ml file instead.
>>
>> thanks for the pointer to ppx_import - at some point i'll probably get
>> annoyed enough to use it :) though as you advise, i'll maintain the current
>> code for a while first, and see how painful it is to add fields to the
>> record in three places every time.
>>
>> martin
>>
>>
>> On Mon, Aug 18, 2014 at 10:54 PM, Gabriel Scherer
>> [email protected] [ocaml_beginners] <
>> [email protected]> wrote:
>>
>>>
>>>
>>> You may be interested in this long caml-list thread about precisely this
>>> question:
>>>   https://sympa.inria.fr/sympa/arc/caml-list/2012-10/msg00205.html
>>> The short answer is "there is no well-understood way to do better
>>> without design hacks".
>>>
>>> Some people have designed meta-programming tools to macro-away some of
>>> the boilerplate (eg. recently https://github.com/whitequark/ppx_import
>>> ). I would recommend first trying to do it the usual way, to get a feeling
>>> of how sufferable it actually is.
>>>
>>>
>>> On Tue, Aug 19, 2014 at 7:50 AM, Martin DeMello [email protected]
>>> [ocaml_beginners] <[email protected]> wrote:
>>>
>>>>
>>>>
>>>> I'm learning my way around the module system, and trying to write a
>>>> small Environment module that creates a record based on a given type. My
>>>> code works, but it looks like i had to essentially write out the record
>>>> definition thrice. Is there a better way to do this?
>>>>
>>>> Here's the definition of the module
>>>>
>>>> /--------------------------------
>>>> $ cat environment.mli
>>>>
>>>> module type ENV = sig
>>>>   type dict
>>>>
>>>>   type env = {
>>>>     dict : dict;
>>>>     op : Types.uop
>>>>   }
>>>> end
>>>>
>>>> module Make (Dict : sig type t end) : ENV with type dict = Dict.t
>>>>
>>>> $ cat environment.ml
>>>>
>>>> module type ENV = sig
>>>>   type dict
>>>>
>>>>   type env = {
>>>>     dict : dict;
>>>>     op : Types.uop
>>>>   }
>>>> end
>>>>
>>>> module Make (Dict : sig type t end) = struct
>>>>   type dict = Dict.t
>>>>
>>>>   type env = {
>>>>     dict : dict;
>>>>     op : Types.uop
>>>>   }
>>>> end
>>>>
>>>> \--------------------------------
>>>>
>>>> and I'm using it in the following code:
>>>>
>>>> /--------------------------------
>>>> module Evaluator =
>>>>   functor (Env : ENV) ->
>>>>   functor (E : ENGINE with type dict = Env.dict) ->
>>>>   struct ... end
>>>>
>>>> module Env = Environment.Make (Trie)
>>>>
>>>> module Eval = Evaluator.Evaluator (Env) (TrieEngine)
>>>> \--------------------------------
>>>>
>>>> martin
>>>>
>>>>
>>>>
>>>>
>>>
>>
>>
>>
>  
>