implement a new var @*ARGFILES listing paths for @*ARGS that are existing files

[tbrowder]

The Problem

Iterating over $*ARGFILES throws an error if the system tries to get a handle on a non-existent file.

Expected Behavior

Ability to iterate over only valid file handles as the name implies.

Actual Behavior

Throws on non-existent files.

Steps to Reproduce

$ rm t
$ cat t.p6
say($_.path) for $*ARGFILES;
$ perl6 t.p6
Failed to open file /path/to/t: No such file or directory
  in block <unit> at t.p6 line 1

Environment

Debian 9, 64-bit.
$ perl6 -v
This is Rakudo version 2018.06 built on MoarVM version 2018.06
implementing Perl 6.c.

Solution

Create the new dynamic variable simultaneously with the creation of @*ARGS. It should contain the paths of the elements of @*ARGS that are existing, readable files.

[ugexe]

What does "if the file exist" mean to different users? Does it exist at the time the program starts? Does it exist at the moment it is iterated over by $*ARGFILES? I'm not sure a pragma can properly capture all the valid variations one might consider.

A naive solution:

BEGIN @*ARGS = @*ARGS.grep(!*.starts-with("-")).grep(*.IO.e);
say($_.path) for $*ARGFILES;

[tbrowder]

In my naive view, I see $*ARGFILES reflecting the current file state of CLI @*ARGS when the program starts. That's the only way I've used Perl scripts (P5 or P6) in my years of use since 1993.

[tbrowder]

I think a better solution is what you suggested, but make it a new dynamic variable: @*ARGFILES. It would be created along with @*ARGS but would just contain the paths of input args that are valid files. I’m renaming and rewording this issue.

[JJ]

@ugexe It simply means valid filehandles. Right now, as Tom has indicated, $*ARGFILES does create a filehandle for non-existing or invalid files, only nothing can be done with it other than capturing the exception when it's used.

[lizmat]

Feels to me $*ARGFILES should return a Failure rather than throw.

[tbrowder]

Yes, then that would satisfy my use case and be a very useful tool, especially if I could iterate it like this:

for $*ARGFILES -> $handle {
    next if !$handle;
    say $handle.path
}

[ugexe]

@JJ It was a rhetorical question. What “valid file handle” means isn’t so clear; backlog the chat channel the last few days to see others with a similar informed opinion and explanation.