[m-rev.] for review: specialise file copying in the compiler

[Zoltan Somogyi]

2022-04-23 22:38 GMT+10:00 "Julien Fischer" <jfischer at opturion.com>:
> I agree and when the necessary machinery exists (see below) will do that.
> I will add a comment about that for now.
> 
> Actually, there are a few things that should happen here:
> 
> 1. If the OS or platform provides a file copy operation (e.g. CopyFile()
> on Windows, java.nio.file.Files.copy()) we should use that in preference
> to either calling an external command or using the Mercury implementation.
> 
> 2. We should add a way to tell the compiler not to even try copying a
> file using an external command. (This would be useful on Windows, where
> the copy command is a poor substitute for cp.)

I didn't know either of those things, but they are valid points.

> 3. We should add some sort of copy_file predicate to the standard
> library.  This is slightly iffy since file copy operations in most
> programming language standard libraries are really "copy the file and
> preserve relevant metadata where possible".

In at least some cases, preserving the modification time is something
that we want to *avoid*, though I am not sure you include that in "metadata".

> On balance, I think it would
> be a worthwhile addition and we can make it work well enough on the
> platforms we support.

If you say so; I don't know about non-Unix platforms to say yes or no.

> There was the small matter of the 22.01 release between then and now ;-)

Of course. I was just surprised that you seemed to abandon the agreed-on
approach.

> Do you have any objections to committing this with the added comment?

No objection.

> Another question: should the stream foldls in the stream module be
> modified to reduce stack usage in debug grades (as some of the ones
> in the io module have been)?

I don't think they should be modified; I think there should be separate
versions of the relevant predicates that do chunking, with an extra
chunk size parameter, since that does vary with expected max iteration length.

Zoltan.