CAML Light system functions etc.

CAML Light system functions etc.

[John Harrison]

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A few quick questions about CAML Light:

(1) Is there an interface to "tempnam" or something similar? (For creating
unique temporary filenames). I looked in the "unix" library but couldn't
find anything -- I think it'd be a convenient addition.

(2) I'm not really convinced that integrating signal and exception handling
is a good idea; it's neither pleasant nor efficient to always have to worry
about signal exceptions popping up. Is it possible to make SIGINT terminate
the evaluation of the current toplevel phrase, without passing a signal
exception to the currently executing function?

(3) Is there some hook to allow a user-defined function to be called after
the evaluation and printing of each toplevel phrase? This would be nice for
reporting run statistics etc.

Thanks,

John.

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John Harrison                   | email: jharriso@ra.abo.fi
Åbo Akademi University          | web:   http://www.abo.fi/~jharriso/
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Re: CAML Light system functions etc.

[Xavier Leroy]

> (1) Is there an interface to "tempnam" or something similar? (For creating
> unique temporary filenames). I looked in the "unix" library but couldn't
> find anything -- I think it'd be a convenient addition.

It is a SMOP (Small Matter Of Programming). Here is the function I use:

let temp_file base suffix =
  let rec try_name counter =
    let name = "/tmp/" ^ base ^ string_of_int counter ^ suffix in
    if Sys.file_exists name then try_name (counter + 1) else name
  in try_name (Unix.getpid())

> (2) I'm not really convinced that integrating signal and exception handling
> is a good idea;

Signal handlers registered with Unix.signal are arbitrary functions;
They can raise exceptions, or do anything else a function can do.

However, it is true that there is only one way to abort other
computations from a signal handler, which is to raise an exception.

> it's neither pleasant nor efficient to always have to worry
> about signal exceptions popping up.

Shall I read this as ``I use (try ... with _ -> ...) all the time because
I'm too sloppy to figure out exactly which exceptions I should trap'' ?
That's a dangerous thing to do, since any heap allocation can trigger
the Out_of_memory exception.

> Is it possible to make SIGINT terminate
> the evaluation of the current toplevel phrase, without passing a signal
> exception to the currently executing function?

I'm afraid not. The language has only one non-local control structure:
exceptions.

> (3) Is there some hook to allow a user-defined function to be called after
> the evaluation and printing of each toplevel phrase? This would be nice for
> reporting run statistics etc.

No, there isn't.

Regards,

- Xavier Leroy

Re: CAML Light system functions etc.

[John Harrison]

| > (1) Is there an interface to "tempnam" or something similar? (For creating
| > unique temporary filenames). I looked in the "unix" library but couldn't
| > find anything -- I think it'd be a convenient addition.
|
| It is a SMOP (Small Matter Of Programming). Here is the function I use:

Yes, I ended up doing something using the PID. But then most library
functions are a SMOP; it still seems reasonable to provide the ones that
users are going to need. At least you and I needed this one.

| > it's neither pleasant nor efficient to always have to worry
| > about signal exceptions popping up.
|
| Shall I read this as ``I use (try ... with _ -> ...) all the time because
| I'm too sloppy to figure out exactly which exceptions I should trap'' ?
| That's a dangerous thing to do, since any heap allocation can trigger
| the Out_of_memory exception.

That's an all-too-accurate reading! Except that I could perfectly well have
a common exception "MYERR" and just use "try ... with MYERR(_) -> ...". I
wouldn't object to the extra typing, but I guess it would be significantly
less efficient. Is that true? I suppose I could try it and find out.

| > (3) Is there some hook to allow a user-defined function to be called after
| > the evaluation and printing of each toplevel phrase? This would be nice for
| > reporting run statistics etc.
|
| No, there isn't.

Well, since you excel at reading between the lines, you can read my question
as "what a great idea it would be to add some hook... wouldn't it?" My guess
is that it would be easy for a CAML-Light expert to add, since the
interpreter's read-eval-print loop itself seems to be written in CAML.

Cheers,

John.