Re: [Caml-list] Ocaml compiler documentation

[Simon Cruanes <simon.cruanes.2007@m4x.org>]

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Le Thu, 03 Apr 2014, David Allsopp a écrit :
> Yotam Barnoy wrote:
> > 2. What is demonstrated in lines 114-117 regarding polymorphic variant row fields:
> > 
> >  | Rtag of label * bool * core_type list
> >        (* [`A]                   ( true,  [] )
> >           [`A of T]              ( false, [T] )
> >           [`A of T1 & .. & Tn]   ( false, [T1;...Tn] )
> >           [`A of & T1 & .. & Tn] ( true,  [T1;...Tn] )
> >         *)
> >
> > What does the bool value represent?
> 
> It indicates that the constructor is constant, or that one of the types in the conjunction is "empty" (i.e. constant - I don't know what Jacques' terminology for that is!)

I might miss something, but wouldn't this be more readable if a variant
was used instead of booleans? Say,

type includes_constant =
    | IncludesConstant
    | DoesNotIncludeConstant

...
    | RTag of label * includes_constant * core_type list
        (*  [`A]            (IncludesConstant, [])
            [`A of T]       (DoesNotIncludeConstant, [T])
....

It would also be easier to extend. That's just nitpicking but I think it
would make the code more explicit by itself.

In addition, I never heard about conjunctions in variants, so I'm happy
Yotam started this initiative...

Cheers,

-- 
Simon

http://weusepgp.info/
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