Re: a junction or not
Larry Wall wrote: I think I've mentioned before that .perl autothreads. It's the final (low-level) stringification of a junction that slaps the appropriate quantifier around that, I suspect. Please bear with me; I'm starting to get a little lost: are you telling me that $j.perl does what I'd expect of an indeterminate item, and that the trick is in getting a perlization of the Junction itself? If so, cool. So maybe $j.Str returns the eigenstring, while prefix:~ autothreads. Or maybe there's a method named .eigenstring or some such for use by print and say and anyone else who absolutely must end up with something printable. Or maybe there's a method that returns a frozen reference that masquerades as the Junction, but doesn't trigger autothreading. Or would that be opening up an infinitely regressing can of worms? I don't know; I've got this gut feeling that something's off here, but I can't quite put my finger on what it is. Although, maybe I can. As written (I believe), .perl generates a String representation of whatever code is needed to build the object that called it. However, there may come a point somewhere down the road where you'll want .perl to instead return a parse-tree of that code, with the ability to stringify appropriately. If you've written a separate .eigenstring function to perform the same purpose with Junctions, or you've set it up so that prefix:~ autothreads while Junction.Str returns the eigenstring, that will potentially be two functions that will need to be rewritten. More generally, a programmer who writes a function that operates on an Object (and thus autothreads when given a Junction) will be forced to decide between writing a second Junction-aware version if he wants to treat the Junction as a Junction instead of autothreaded Objects, or not bothering and thus not allowing the function to manipulate a Junction directly. In short, you have to reinvent the wheel every time the to Junction or not to Junction question arises. Providing a means to momentarily disable a Junction's autothreading properties would, in one fell swoop, solve every instance of this problem. At least, I think it would. If it wouldn't, it would at least solve a large swath of them. -- Jonathan Dataweaver Lang
Re: a junction or not
Jon Lang wrote:
Darren Duncan wrote:
Jon Lang wrote:
Larry Wall wrote:
This is basically a non-problem. Junctions have one public method,
.eigenstates, which is vanishingly unlikely to be used by accident by
any mere mortal any time in the next 100 years, give or take a year.
If someone does happen to be programming quantum mechanics in Perl 6,
they're probably smart enough to work around the presence of a
reserved--well, it's not even a reserved word-- a reserved method name.
Actually, the problem isn't with '.eigenstates'; the problem is with
'.perl'. If I'm viewing a Junction of items as a single indeterminate
item, I'd expect $J.perl to return a Junction of the items' perl by
default. Admittedly though, even that isn't much of an issue, seeing
as how you _can_ get that result by saying something to the effect of
Junction of $J.eigenstates.«perl - the only tricky part being how to
decide which kind of junction to use (e.g., any, all, one, none) when
putting the perl-ized eigenstates back together. (And how _would_ you
do that?) This would represent another corner-case where the
programmer would be tripped up by a simplistic understanding of what a
Junction is; but being a corner-case, that's probably acceptable.
I would assume that invoking .perl on a Junction would result in Perl code
consisting of the appropriate any/all/etc expression. -- Darren Duncan
Tough to parse, though; and feels like a kludge. I expect better of Perl 6.
What do you mean by tough to parse and feels like a kludge? Isn't the point
of .perl that it results in a string of Perl 6 code that is a Perl 6 value
expression? I wouldn't expect that a Perl 6 expression to result in a Junction
is any more difficult to parse than the source code returning an Array or some such.
For example, if you have:
my $choice = any(1..10);
Then $choice.perl should result in code like any(1..10). Or $choice.perl
would approximately be short for the expression:
'any('~($choice.eigenstates.map:{ $_.perl }.join(','))~')'
... except that the .perl of $choice would also be smart enough to pick
'any'/'all'/etc based on what its Junction value actually is.
Such as that seems perfectly elegant and uncomplicated to me.
If you had a problem with that, then I would expect you'd have a problem with
.perl in general for any value, particularly Array etc values.
-- Darren Duncan
Re: a junction or not
Darren Duncan wrote:
Jon Lang wrote:
Darren Duncan wrote:
I would assume that invoking .perl on a Junction would result in Perl
code
consisting of the appropriate any/all/etc expression. -- Darren Duncan
Tough to parse, though; and feels like a kludge. I expect better of Perl
6.
What do you mean by tough to parse and feels like a kludge?
If I'm understanding Larry correctly, then given:
my $choice = any(1..10);
$choice.perl will return the same thing that the following would:
any($choice.eigenstates.«perl)
That is, it would return a Junction of Str, not a Str. So the
question is how to get something that returns an expression to the
effect of:
'any(' ~ $choice.eigenstates.«perl.join(',') ~ ')'
Or, if I'm reading Larry incorrectly and $choice.perl provides the
latter, how do you get the former (without knowing ahead of time that
$choice is an any-junction)?
--
The other question is: given $choice as defined above, how do I find
out which type of junction it is? Do I somehow call something that
would produce the latter string, and then extract the first word from
it? Or is there a more direct way to find out which kind of Junction
you're dealing with?
--
Jonathan Dataweaver Lang
Re: a junction or not
On 2009-Mar-17, at 2:16 am, Jon Lang wrote:
$choice.perl will return the same thing that the following would:
any($choice.eigenstates.«perl)
That is, it would return a Junction of Str, not a Str. So the
question is how to get something that returns an expression to the
effect of:
'any(' ~ $choice.eigenstates.«perl.join(',') ~ ')'
say $choice.perl
...which will ultimately call (junction-of-.perl's).Str, and
Str(Junction:) is what produces the any(XXX) string. [Unless it
ends up being implemented some other way, of course!]
The other question is: given $choice as defined above, how do I find
out which type of junction it is?
I guess really Junctions need two public methods: .eigenstates for the
values, and, er, .eigenop(?!) to return how they're joined -- I'm
thinking it would return a code ref, i.e. any, all, etc.
-David
r25880 - docs/Perl6/Spec
Author: lwall
Date: 2009-03-18 02:28:39 +0100 (Wed, 18 Mar 2009)
New Revision: 25880
Modified:
docs/Perl6/Spec/S03-operators.pod
docs/Perl6/Spec/S04-control.pod
Log:
create more semantic distance between terms and 0-ary functions
Modified: docs/Perl6/Spec/S03-operators.pod
===
--- docs/Perl6/Spec/S03-operators.pod 2009-03-18 01:03:18 UTC (rev 25879)
+++ docs/Perl6/Spec/S03-operators.pod 2009-03-18 01:28:39 UTC (rev 25880)
@@ -12,9 +12,9 @@
Maintainer: Larry Wall la...@wall.org
Date: 8 Mar 2004
- Last Modified: 12 Mar 2009
+ Last Modified: 17 Mar 2009
Number: 3
- Version: 158
+ Version: 159
=head1 Overview
@@ -303,14 +303,6 @@
its left, so it binds tighter than comma on the left but looser than
comma on the right--see List prefix precedence below.
-=item *
-
-0-ary functions
-
-self
-undef
-rand
-
=back
=head2 Method postfix precedence
@@ -1009,7 +1001,7 @@
to C$_ in Perl 6.
There is no unary Crand function in Perl 6, though there is a C.rand
-method call and a 0-ary Crand term.
+method call and an argumentless Crand term.
=over
@@ -1746,7 +1738,7 @@
The function can be 0-ary as well:
-() ... rand # list of random numbers
+() ... { rand }# list of random numbers
The function may also be slurpy (*-ary), in which case all the
preceding values are passed in (which means they must all be cached
@@ -3627,7 +3619,7 @@
then you shouldn't worry about it, because unlike previous versions,
Perl 6 never guesses whether the next thing is a term or operator.
In this case it is always expecting a term unless Cfoo is predeclared
-to be a 0-ary sub.]
+to be a type or value name.]
The upgrade never happens on the blunt end of a hyper. If you write
Modified: docs/Perl6/Spec/S04-control.pod
===
--- docs/Perl6/Spec/S04-control.pod 2009-03-18 01:03:18 UTC (rev 25879)
+++ docs/Perl6/Spec/S04-control.pod 2009-03-18 01:28:39 UTC (rev 25880)
@@ -12,9 +12,9 @@
Maintainer: Larry Wall la...@wall.org
Date: 19 Aug 2004
- Last Modified: 4 Mar 2009
+ Last Modified: 17 Mar 2009
Number: 4
- Version: 73
+ Version: 74
This document summarizes Apocalypse 4, which covers the block and
statement syntax of Perl.
@@ -95,7 +95,7 @@
a variable in the current package.
The new Cconstant declarator introduces a lexically scoped name
-for a compile-time constant, either a variable or a 0-ary sub, which
+for a compile-time constant, either a variable or named value, which
may be initialized with a pseudo-assignment:
constant Num $pi = 3;
