Re: [Caml-list] some beautiful OCaml code

[Malcolm Matalka <mmatalka@gmail.com>]

Hey, author here,

The problem polymorphic variants are solving here is that if you want to
sequence unrelated functions but return their errors, you have to join
their return types with the return types of the function that is calling
them.  Polymorphic variants basically do this for you without every
function defining its own error return variant.

This, so far, is the only time I have found polymorphic variants the
best solution for a problem in Ocaml.

/Malcolm

David MENTRE <dmentre@linux-france.org> writes:

> Hello OCaml experts,
>
> 2013/1/9 Francois Berenger <berenger@riken.jp>:
>> There is a full blog post about it there:
>>
>> http://functional-orbitz.blogspot.se/2013/01/introduction-to-resultt-vs-exceptions.html
>
> Regarding this blog post, the final code is using Polymorphic Variants
> (http://caml.inria.fr/pub/docs/manual-ocaml/manual006.html#toc36).
> E.g.
> """
>     | _ ->
>       Error (`Bad_line s)
> """
>
> I never fully grasped polymorphic variants compared to regular ones
> but I always had the feeling the polymorphic variants where less safe
> that variants because they would allow more possibility to mix
> unrelated things[1].
>
> Are the use of polymorphic variant mandatory to write code
> Return-Value-style code or can regular variants be used?
>
> Best regards,
> david
>
> [1] Of course this ability is the very thing that is of interest to
> people using polymorphic variants.