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

[Jeremy Yallop <yallop@gmail.com>]

On 30 April 2015 at 21:57, Ömer Sinan Ağacan <omeragacan@gmail.com> wrote:
> Let's talk on an example:
>
> -- contents of TestData.ml
>   type foo = Foo of int
>
> -- contents of main
>   open TestData
>
>   let global_ref : int ref = ref 0
>
>   let gen_inc =
>     .< let _ = global_ref := !global_ref + 1 in () >.

You can improve the output here (and everywhere else that you use
global_ref in a quotation) by putting the global reference in a
separate file, so that MetaOCaml can persist it as a path:

   let gen_inc =
     .< let _ = Globals.global_ref := !Globals.global_ref + 1 in () >.

>   let gen_write i =
>     .< match i with
>        | Foo i -> global_ref := i
>      >.

In this case the problem is that 'i' is a local variable bound to a
current-stage value.  It's better to make it a future-stage (code)
expression, and splice that in:

   let gen_write i =
     .< match .~i with
        | Foo i -> global_ref := i
      >.

You'll also need to change the call:

    gen_write .<Foo 10>.

>   let gen_cls_wrt cls =
>     .< global_ref := cls () >.

This time there are two problems.  First, cls is local, as with 'i'
above.  Second, 'cls' is a closure (function), so it doesn't have a
printed representation.  You can address the problem by making cls
either a code value or a top-level path, e.g.

     .< Globals.global_ref := Globals.cls () >.

or

     .< Globals.global_ref := .~cls () >.

With these changes the program runs without warnings or errors and
generates compilable code without CSP comments.

> * I don't know if this is MetaOCaml related, but output of this program is
>   interleaved. Instead of printing a line than code it prints two lines and
>   then two code etc. How is this possible??

The interleaving is probably due to internal buffering in the format library.

Jeremy.