What should file test operators return?
At the moment the file test operators that I expect to return true or
false do, but the true is the filename. I expected a boolean, for no
other reason than Perl 6 has them so it might as well use them. The
section on Smart Matching in S03 says that the ~~ doesn't have to
return a boolean, but aside from things liek :s, :M, and :A, what good
would it be not to? I'm happy to update S16 with whatever the answer
is. :)
Here's my code example that motivates this question. For a Llama6
exercise with file test operators, I wanted to create a little table:
for @files - $file {
printf %-70s %s %s %s\n,
$file,
$file ~~ :r,
$file ~~ :w,
$file ~~ :x;
}
I get the filename for each part:
foo foo foo
Which I wanted to work like this perl5 (not that I care if it's
different, I just have to explain it to reader)
#!/usr/bin/perl5
foreach ( glob( * ) )
{
printf %30s %s %s %s\n, $_, -r, -w, -x
}
With the Pugs 6.2.13 (r15868), only the ~~ form seems to work, but is
that going to be any different than the other two forms?
pugs ( Talks ~~ :r ).say
Talks
Bool::True
pugs ( Talks ~~ :d ).say
Talks
Bool::True
pugs Talks.TEST(:s).say
*** No such method in class Str: TEST
at interactive line 1, column 1-21
pugs Talks.:s
Internal error while running expression:
***
Unexpected :s
expecting ., \187, , =, operator name, qualified
identifier, variable name, ..., --, ++, i, array subscript,
hash subscript or code subscriptat interactive line 1, column 9
pugs Talks.:d
Internal error while running expression:
***
Unexpected \:
expecting ., \187, , =, operator name, qualified
identifier, variable name, ..., --, ++, i, array subscript,
hash subscript or code subscriptat interactive line 1, column 9
Re: What should file test operators return?
Hi, brian d foy wrote: At the moment the file test operators that I expect to return true or false do, but the true is the filename. that helps chaining of file test: $fn ~~ :t ~~ :x or something. If you want a boolean, use ? $fn ~~ :x or something. HTH, Moritz -- Moritz Lenz http://moritz.faui2k3.org/ - http://sudokugarden.de/ - http://perl-6.de/ signature.asc Description: OpenPGP digital signature
Re: What should file test operators return?
On 13/04/07, Moritz Lenz [EMAIL PROTECTED] wrote:
If you want a boolean, use
? $fn ~~ :x
or something.
Definitely or something. Unary ? has the wrong precedence there.
You could write:
for @files - $file {
printf %-70s %s %s %s\n,
$file,
true $file ~~ :r,
true $file ~~ :w,
true $file ~~ :x;
}
which could, of course be hyperoperated:
for @files - $file {
printf %-70s %s %s %s\n,
$file,
true $file ~~ (:r, :w, :x);
}
Maybe there also needs to be a boolean conversion for printf
(perhaps %t for true?):
for @files - $file {
printf %-70s %t %t %t\n,
$file,
$file ~~ :r,
$file ~~ :w,
$file ~~ :x;
}
Which leads to:
for @files - $file {
printf %-70s %t %t %t\n,
$file,
$file ~~ (:r, :w, :x);
}
Damian
Re: What should file test operators return?
Damian Conway skribis 2007-04-13 20:01 (+1000): Maybe there also needs to be a boolean conversion for printf (perhaps %t for true?): I often use [ ] and [X] to represent true and false in text output. They resemble checkboxes. I don't think printf needs a boolean output template, but it would be nice if it were configurable. -- korajn salutojn, juerd waalboer: perl hacker [EMAIL PROTECTED] http://juerd.nl/sig convolution: ict solutions and consultancy [EMAIL PROTECTED]
Re: What should file test operators return?
On Fri, Apr 13, 2007 at 10:29:43AM +0100, Moritz Lenz wrote: Hi, brian d foy wrote: At the moment the file test operators that I expect to return true or false do, but the true is the filename. that helps chaining of file test: $fn ~~ :t ~~ :x or something. If you want a boolean, use ? $fn ~~ :x or something. It might also be useful when the test is being applied to a junction - it gives the effect of grep. --
Re: What should file test operators return?
On Apr 12, 2007, at 14:52 , brian d foy wrote: At the moment the file test operators that I expect to return true or false do, but the true is the filename. I expected a boolean, for no other reason than Perl 6 has them so it might as well use them. This is documented somewhere already. Pugs does not implement the spec as documented, though. File tests are supposed to return something which: - behaves as a Bool - stringifies as a filename - numifies as a file size or as a time, if appropriate - propagates a stat object (obviating perl5's magic _) Current Pugs only does the first three, sort of: the size and time operators return numeric, the others string, all behave appropriately if used as booleans. This means you mostly get the expected results for chained tests, at the price of every operator doing its own stat(). My impression is that junction types aren't really there yet, so this is the best that can currently be done. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED] system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED] electrical and computer engineering, carnegie mellon university KF8NH
Re: What should file test operators return?
In article [EMAIL PROTECTED], Brandon S. Allbery KF8NH [EMAIL PROTECTED] wrote: On Apr 12, 2007, at 14:52 , brian d foy wrote: At the moment the file test operators that I expect to return true or false do, but the true is the filename. I expected a boolean, for no other reason than Perl 6 has them so it might as well use them. This is documented somewhere already. Pugs does not implement the spec as documented, though. That's part of the problem: finding that somewhere, then makign the other somewhere's agree with it.
Re: What should file test operators return?
In article [EMAIL PROTECTED], Moritz Lenz [EMAIL PROTECTED] wrote: brian d foy wrote: At the moment the file test operators that I expect to return true or false do, but the true is the filename. that helps chaining of file test: $fn ~~ :t ~~ :x or something. That's fine, but the example in S16 shows that as a junction: $fh ~~ :t :x I don't mind the answer being whatever it is as long as it's really the answer that I can tell newbies and point to in the docs. :)
Re: What should file test operators return?
In article [EMAIL PROTECTED], Brandon S. Allbery KF8NH [EMAIL PROTECTED] wrote: File tests are supposed to return something which: - behaves as a Bool - stringifies as a filename - numifies as a file size or as a time, if appropriate - propagates a stat object (obviating perl5's magic _) Current Pugs only does the first three, sort of: the size and time operators return numeric, the others string, all behave appropriately if used as booleans. I'm not sure Pugs does that right. The file named 0 (zero) seems to behave inappropriately. In this example, foo and 0 are real files, and not there is not a file that exists: pugs foo ~~ :e foo pugs true foo ~~ :e Bool::True pugs not there ~~ :e Bool::False pugs true not there ~~ :e Bool::False pugs 0 ~~ :e 0 pugs true 0 ~~ :e Bool::False Again, I don't really mind whatever the answer is as long as I can document it. :)
Re: What should file test operators return?
In article [EMAIL PROTECTED], Moritz Lenz [EMAIL PROTECTED] wrote: Hi, brian d foy wrote: At the moment the file test operators that I expect to return true or false do, but the true is the filename. that helps chaining of file test: $fn ~~ :t ~~ :x or something. I thought that returning a stat buffer was supposed to handle the case of chained file test operators. S16 will also need a fix-up for this text, I think: Also note that, for the superuser on the local filesystems, the :r, :R, :w, and :W tests always return 1,
Re: What should file test operators return?
On Apr 13, 2007, at 9:04 , brian d foy wrote: In article [EMAIL PROTECTED], Brandon S. Allbery KF8NH [EMAIL PROTECTED] wrote: File tests are supposed to return something which: - behaves as a Bool - stringifies as a filename - numifies as a file size or as a time, if appropriate - propagates a stat object (obviating perl5's magic _) Current Pugs only does the first three, sort of: the size and time operators return numeric, the others string, all behave appropriately if used as booleans. I'm not sure Pugs does that right. The file named 0 (zero) seems to I'm not surprised; as I said, the current behavior is basically a placeholder. In the final implementation the real value will be the stat structure, which won't have the 0 vs. '0' ambiguity. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED] system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED] electrical and computer engineering, carnegie mellon university KF8NH
Re: What should file test operators return?
On Fri, Apr 13, 2007 at 08:01:13PM +1000, Damian Conway wrote: : Maybe there also needs to be a boolean conversion for printf : (perhaps %t for true?): Seems insufficiently general. However, I note that booleans are an enum, and by default stringify to Bool::True or Bool::False. Maybe %t stands for terse, which stringifies to True and False, and in general stringifies any enum to its unqualified name rather than its qualified name. Kind of a shame %e is taken. On the other hand, maybe wasting a printf char on this is still insufficiently general, and it should just be a .terse or .key method of some sort feeding to a normal %s. Larry
Re: What should file test operators return?
On Thu, Apr 12, 2007 at 01:52:50PM -0500, brian d foy wrote:
: At the moment the file test operators that I expect to return true or
: false do, but the true is the filename.
You've just dug up a pugsian fossil.
: I expected a boolean, for no
: other reason than Perl 6 has them so it might as well use them. The
: section on Smart Matching in S03 says that the ~~ doesn't have to
: return a boolean, but aside from things liek :s, :M, and :A, what good
: would it be not to? I'm happy to update S16 with whatever the answer
: is. :)
The intent of moving from the
-r -w -x $file
form to the
$file ~~ :r :w :x
form was to get rid of the klunky, inflexible statbuffer propagation
mechanism, which (without an temp var) could only do and and not
or, and didn't work well syntactically in when statements. Plus
it forced the user to worry about statbuf caching, which probably just
ought to timeout automatically since it assumes we're the only person
accessing the filesystem, a bogus assumption in the face of any kind
of multiprocessing.
So the new filetests just return a simple value, generally Bool or Num.
To get a statbuf object you now use an explicit stat or lstat. Such an
object should probably stringify to Stat('filename') or some such, so
that the filename 0 comes out Stat('0').
I will attempt to clarify S03, though my brain is still a little
fuzzy this week for a variety of unrelated reasons.
: Here's my code example that motivates this question. For a Llama6
: exercise with file test operators, I wanted to create a little table:
:
:for @files - $file {
: printf %-70s %s %s %s\n,
: $file,
: $file ~~ :r,
: $file ~~ :w,
: $file ~~ :x;
: }
I think I would now write that more like:
for @files - $file {
given stat $file {
printf %-70s %s %s %s\n, $file, .:r, .:w, .:x;
}
}
: Which I wanted to work like this perl5 (not that I care if it's
: different, I just have to explain it to reader)
:
:#!/usr/bin/perl5
:foreach ( glob( * ) )
: {
: printf %30s %s %s %s\n, $_, -r, -w, -x
: }
:
:
: With the Pugs 6.2.13 (r15868), only the ~~ form seems to work, but is
: that going to be any different than the other two forms?
The current pugs implementation is just translating to the old form
underneath, so it's not surprising it's a bit off. That's the sort
of thing that happens when the language designer gives the language
implementor whiplash. However, I rather suspect the interpersonal
metaphorical meaning was lost on the physicist/comic who decided that
the 3rd derivative of position should be called jerk. :)
Larry
Re: What should file test operators return?
In article [EMAIL PROTECTED], Larry Wall
[EMAIL PROTECTED] wrote:
On Thu, Apr 12, 2007 at 01:52:50PM -0500, brian d foy wrote:
: Here's my code example that motivates this question. For a Llama6
: exercise with file test operators, I wanted to create a little table:
:
:for @files - $file {
: printf %-70s %s %s %s\n,
: $file,
I think I would now write that more like:
for @files - $file {
given stat $file {
printf %-70s %s %s %s\n, $file, .:r, .:w, .:x;
}
}
Hmmm, that's a good little bit of code, as was Damian's use of the
hyper-operator. The trick is to figure how how much I can use in Llama
6 without scaring off the reader. :)
I'm actually starting at the back of the book so I know what I have to
put in the front of the book to get that far. In previous Llamas the
file tests operators came before stat, but maybe this answer is a good
end-of-chapter sorta thing.
I'll also have to think about using given {} merely as a topicalizer
too, I guess, although showing it next to an explicit assignment to $_.
:)
Re: What should file test operators return?
I think I need to reread the docs. What's the colon in the method calls for?
(That is, why is it $stat_obj.:r instead of just $stat_obj.r ?)
On 4/13/07, brian d foy [EMAIL PROTECTED] wrote:
In article [EMAIL PROTECTED], Larry Wall
[EMAIL PROTECTED] wrote:
On Thu, Apr 12, 2007 at 01:52:50PM -0500, brian d foy wrote:
: Here's my code example that motivates this question. For a Llama6
: exercise with file test operators, I wanted to create a little table:
:
:for @files - $file {
: printf %-70s %s %s %s\n,
: $file,
I think I would now write that more like:
for @files - $file {
given stat $file {
printf %-70s %s %s %s\n, $file, .:r, .:w, .:x;
}
}
Hmmm, that's a good little bit of code, as was Damian's use of the
hyper-operator. The trick is to figure how how much I can use in Llama
6 without scaring off the reader. :)
I'm actually starting at the back of the book so I know what I have to
put in the front of the book to get that far. In previous Llamas the
file tests operators came before stat, but maybe this answer is a good
end-of-chapter sorta thing.
I'll also have to think about using given {} merely as a topicalizer
too, I guess, although showing it next to an explicit assignment to $_.
:)
--
Mark J. Reed [EMAIL PROTECTED]
Re: What should file test operators return?
In article [EMAIL PROTECTED], Mark J. Reed [EMAIL PROTECTED] wrote: I think I need to reread the docs. What's the colon in the method calls for? (That is, why is it $stat_obj.:r instead of just $stat_obj.r ?) I can't answer the why question, but the stuff in S02 might help you. Look for generalized adverbial form: http://feather.perl6.nl/syn/S02.html The file test is really an adverbial pair (and see the message about pairs that I just posted). Larry just updated S03 with some clarification on file tests. Look at the section on Changes to Perl 5 Operators http://feather.perl6.nl/syn/S03.html
