Re: [Caml-list] unboxing of unary datatypes

["Nicolas Cannasse" <warplayer@free.fr>]

> Hi all,
>
> I originally had a very calculation intensive program which used a data
> type which looked like:
>
> > type foo = Foo of float
>
> I could just have easily used floats, but I wanted to ensure that I didn't
> do anything stupid (like try to multiply a foo by a float), so I did this
> boxing so the type-checker would help me out.

Hi,

What you might need here are shadow types.
You can define in your ML source file:

type foo = float
let mfoo f f' = f *. f' (* or better let mfoo = ( *. ) *)

and in your interface ( MLI file ) :

type foo
val mfoo : foo -> foo -> foo

then, other modules trying to work with your foo will have to use your set
of operators because they won't know what exactly is "foo".

> Can someone explain this to me?  Why doesn't the compiler optimize out the
> constructor?

Because they don't have the same C raw representation.
There is one more indirection when you use a constructor.
If you want to interface OCaml with C, you have to be sure that the compiler
won't try to optimize things in an incompatible way ( that goes for all
compilers I think... )

Nicolas Cannasse

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