Re: [Caml-list] optional functions in modules

[Yitzhak Mandelbaum <yitzhakm@CS.Princeton.EDU>]

Thanks to everyone who responded.  FWIW, I found the argument in favor of options most compelling as a general approach.

Yitzhak

On May 10, 2012, at 8:55 PM, Yaron Minsky wrote:

> Core's approach to this is to use options.  (Technically, we use a
> type called Or_error.t, which has a useful error message in the
> error-variant, but it's the same idea.)
> 
> On Thu, May 10, 2012 at 2:44 PM, Goswin von Brederlow <goswin-v-b@web.de> wrote:
>> Yitzhak Mandelbaum <yitzhakm@cs.princeton.edu> writes:
>> 
>>> Hi,
>>> 
>>> Is there any "common wisdom" regarding the inclusion of optional functions in a module signature?  The two most obvious approaches involve 1) a pair of boolean flag and a function, where the function raises an exception if unimplemented OR 2) using the option type. I see pros/cons to each approach, but am curious if there's any (unofficial) standard approach.
>>> 
>>> Yitzhak
>>> -----------------------------
>>> Yitzhak Mandelbaum
>> 
>> The extunix module has a trifold solution for this:
>> 
>> * First there is the ExtUnix.All module that has all functions in
>>  it. Functions that are not available raise Not_available with function
>>  name as an argument.
>> 
>> * Second there is ExtUnix.All.have : string -> bool option
>> 
>>  (** [have name]
>>    @return indication whether function [name] is available
>>    - [Some true] if available
>>    - [Some false] if not available
>>    - [None] if not known
>> 
>>    e.g. [have "eventfd"]
>>  *)
>> 
>> * Third there is ExtUnix.Specific containing only functions available on
>>  this platform.
>> 
>> MfG
>>        Goswin
>> 
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> 
> 
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-----------------------------
Yitzhak Mandelbaum