Re: [Caml-list] Problems with printing MetaOCaml generated code

[Leo White <leo@lpw25.net>]

> I don't think this is true, as far as I can see MetaOCaml doesn't have open code
> values that are only runnable in environments that bind free variables in the
> code.
> 
>   # .<a>.;;
>   Error: Unbound value a
>   # let a = 1 in .<a>.;;
>   - : int code = .<1>.
> 
> In this example `.<a>.` didn't mean a code that is just the variable `a`,
> instead, `a` is lifted in code and code is now `.<1>.`.
> 
> I think this automatic lifting is why MetaOCaml doesn't have explicit "lift"
> operation like MetaML does: variables bound in the environment automatically
> lifted, so no open code values are possible.

It is true that MetaOCaml tries to auto-magically lift *some* things for you
(e.g. ints), as in this example. If type information is available, then for known
types it can produce a call to a function such as `Trx.lift_constant_int` to do the
lifting. For other types it will examine the value at run-time and attempt to lift it.
For example, if the value has a "string tag" then it can be represented by a string
literal. If this fails then it will fall back to using true CSP -- which can be run but
cannot be printed.

Personally, I think it is best to avoid this auto-magic and just do your lifting by
hand. The type-based auto-magic doesn't work with polymorphism, whilst the
value-based auto-magic is not parametric.

Regards,

Leo