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

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
>>
>>
>>
>>
>  
>