Re: [Caml-list] Ocaml compiler documentation

[Yotam Barnoy <yotambarnoy@gmail.com>]

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Wow that was awesome! Thanks so much for your help and encouragement, guys!

I think for this file I'll submit a simple PR with only a few minor
clarifications for the less obvious features. I'll also make an 'OCaml
Nuances' page in the wiki for listing some of these less well-known
features.

After that, I think I'll proceed to typing/typedtree.mli, which is the same
AST, only after the typechecker has added types to it.



On Thu, Apr 3, 2014 at 6:46 AM, David Allsopp <dra-news@metastack.com>wrote:

> Simon Cruanes wrote:
> > 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
>
> Possibly (it certainly can't make any difference for efficiency, as type
> bool is simply a two-constructor variant itself!). I guess historically the
> worry would be conflicting names between different types, but that's not a
> problem now.
>
> > In addition, I never heard about conjunctions in variants, so I'm happy
> > Yotam started this initiative...
>
> +1!
>
> I already knew about conjunctions (it is worth perusing that section of
> the manual as most, if not all, of the weird corner cases are covered in
> there somewhere) but not how it was implemented in the parser/type checker!
>
>
> David
>
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