Should !~~ /regex/ set $/?
The subject says it all: should !~~ with a regex on the RHS set $/? Cheers, Moritz -- Moritz Lenz http://moritz.faui2k3.org/ | http://perl-6.de/
Re: [perl #58626] default and when * execute even when another when clause is used
The when statements are just like if statements. After executing one, it goes on to the following statement which does not have to be a conditional statement. That is, you can mix when statements with plain unconditional statements. If multiple when conditions match, it runs all of them. It's more like if statements, not like a C switch statement. --John Stephen Simmons (via RT) wrote: # New Ticket Created by Stephen Simmons # Please include the string: [perl #58626] # in the subject line of all future correspondence about this issue. # URL: http://rt.perl.org/rt3/Ticket/Display.html?id=58626 In the attached code, there is a fairly simple example of a case statement using given/when that has multiple clauses executed. I assumed from my reading of S04 that if one of the when block is taken, when it finishes control exits the innermost given block, though the English is confusing to me. However it doesn't and continues on to both the when * clause and the default clause. Execution: sully:perl6 stephensimmons$ adventure_world/a1b.p6 You are at (0, 0) within region outside. n Oops!; What does n mean? You are at (0, 1) within region outside.
Re: Should !~~ /regex/ set $/?
On Sat, Sep 06, 2008 at 11:44:05AM +0200, Moritz Lenz wrote:
: The subject says it all: should !~~ with a regex on the RHS set $/?
For now I would assume that the meta operator rewrites
$a !~~ $b
to
(not $a ~~ $b)
so .ACCEPTS has no clue that it is dealing with a negated operator.
In other words, it sets $/ just like the normal ~~ operator, but
the boolean sense comes out backwards:
if $a !~~ /foo/ {
# $/ is false
}
else {
# $/ is true
}
Larry
Re: [perl #58626] default and when * execute even when another when clause is used
On Sat, Sep 06, 2008 at 11:38:42AM -0500, John M. Dlugosz wrote:
The when statements are just like if statements. After executing one,
it goes on to the following statement which does not have to be a
conditional statement. That is, you can mix when statements with plain
unconditional statements.
If multiple when conditions match, it runs all of them. It's more like
if statements, not like a C switch statement.
No, when statements also imply a break at the end of the block. It
should never run more than one (unless you explicitly say continue).
You can mix unconditional statements, but any after the first matching
when will not be run (unless you say continue).
If both when * and default are running, it's a small bug,
indicating that the when * {...} got turned into a mere {...}
or ... on the assumption that you don't actually have to test for
the default condition. Which you don't, but it should still run
only one default block, so it should really turn into something like
{...; break}.
Larry
Re: Should !~~ /regex/ set $/?
On Sat, Sep 06, 2008 at 09:41:07AM -0700, Larry Wall wrote: On Sat, Sep 06, 2008 at 11:44:05AM +0200, Moritz Lenz wrote: : The subject says it all: should !~~ with a regex on the RHS set $/? For now I would assume that the meta operator rewrites $a !~~ $b to (not $a ~~ $b) Perl 5 still does exactly this - there is no !~ opcode - the compiler just generates the optree for ! of =~, and it is indistinguishable from it: $ perl -MO=Deparse -e 'print if $^X !~ /perl/' print $_ if not $^X =~ /perl/; -e syntax OK $ perl -MO=Deparse -e 'print if not $^X =~ /perl/' print $_ if not $^X =~ /perl/; -e syntax OK Nicholas Clark
Re: Conceptual question on exception in S04
On Wed, Sep 03, 2008 at 06:44:22PM -0500, John M. Dlugosz wrote: I'm trying to work out some details of this area, but I don't understand what S04 is trying to say. Could someone please point me in the right direction? I'd be happy to then edit the S04 to contribute. In S04, the Exceptions section mentions that $! contains multiple exceptions. So what type is it? Why isn't it @! ? I says that they are thrown as a single new exception. So what type is that new exception? A multi-exception of some kind? No, just the new exception, which merely has to contain the old unhandled exceptions somehow in case the user wants more information. How do you get multiple pending exceptions in the first place? If you mean that exceptions can be thrown (and handled) within the handling of another exception, then the list should be more of a stack. Should the handler then see the topmost one as its topic? If you really did make the whole list the topic then it would be difficult to match. All I care is that we don't discard useful information here. Only the outermost exception needs to be directly matchable against via $!. How would you access the other exceptions in $!, presumably testing them for .defined etc.? I would assume that the $! object can be accessed as an array in that case, unless someone can argue for a different interface. By the way, I'd like to see a user interface where the outer exception is the one printed out in simple form, with the complete cockpit recorder dump of information going into a file that is browser accessible with a click on a link in the error message to more info. Larry
Re: [perl #58626] default and when * execute even when another when clause is used
On Sep 6, 2008, at 10:51 AM, Larry Wall wrote:
On Sat, Sep 06, 2008 at 11:38:42AM -0500, John M. Dlugosz wrote:
The when statements are just like if statements. After executing
one,
it goes on to the following statement which does not have to be a
conditional statement. That is, you can mix when statements with
plain
unconditional statements.
If multiple when conditions match, it runs all of them. It's more
like
if statements, not like a C switch statement.
No, when statements also imply a break at the end of the block. It
should never run more than one (unless you explicitly say continue).
You can mix unconditional statements, but any after the first matching
when will not be run (unless you say continue).
If both when * and default are running, it's a small bug,
indicating that the when * {...} got turned into a mere {...}
or ... on the assumption that you don't actually have to test for
the default condition. Which you don't, but it should still run
only one default block, so it should really turn into something like
{...; break}.
I've set up two identical when blocks, followed by a when * and a
default and all of them run, which is consistent with the behavior
that John describes. The current behavior is no different from a if
EXPR block which is shorter to type, so I'm glad that the intended
behavior is to break out on success.
Patrick merged this with #57652, and there is a comment in the code
that marks this behavioral problem as a todo (in src/parser/actions.pm).
Stephen Simmons
Larry
Re: Conceptual question on exception in S04
Larry Wall larry-at-wall.org |Perl 6| wrote: No, just the new exception, which merely has to contain the old unhandled exceptions somehow in case the user wants more information. OK, so it's more like the inner exception in Microsoft's .NET framework. My C++ exceptions have always had the ability to record multiple stanzas of information, to re-throw and update the picky details with context-specific interpretation. It sounds like what you want is that if there is a pending unhandled exception in dynamic scope, then 'die' or the fresh Exception object's constructor will automatically pick that up as the inner exception. By the way, I'd like to see a user interface where the outer exception is the one printed out in simple form, with the complete cockpit recorder dump of information going into a file that is browser accessible with a click on a link in the error message to more info. Larry I did that about fifteen years ago. The dialog box had a drop-down to show all the layers of information, and also a save button. The format predates XML though, and was designed for high-speed and failsafe logging, so it used control characters instead of XML-like tags. --John
Re: adverbial form of Pairs notation question
On Sat, Sep 06, 2008 at 07:06:30PM +1100, Илья wrote: : Hello there, : what :foo should exactly produce? : At first I was expecting: : foo = : but in Rakudo: : foo = [] : and it looks like the right thing on the other hand. : : (I have started this topic in the November mail list : http://groups.google.com/group/november-wiki/browse_thread/thread/939216e836f69baa : ) As mentioned on irc, it should do the same thing as foo = (). The question is whether () in item context promotes to []. I don't think it ought to, since () is really the only way we have of writing NIL in Perl 6, and [] isn't really NIL. And I think it would be odd to have *two* discontinuities: item (1,2) # [1,2] item (1)# (1) item () # []??? One discontinuity is bad enough: item (1,2) # [1,2] item (1)# (1) item () # () Essentially, the () value lazily produces undef if you actually try to access its (first) value, whereas () in list context merely interpolates nothing. On the other hand, if () isn't NIL, then we have item (1,2) # [1,2] item (1)# (1) item () # Failure of some sort But basically I think NIL is a mild form of failure anyway, so it's fine with me if () is a form of failure that is smart enough to be itself in item context but interpolate nothing into list context. Another view is that it's a kind of empty capture that is smart enough to convert to failure in item context. Possibly the right side of a pair should be capture context rather than item context. Not sure about that... Larry
Re: adverbial form of Pairs notation question
On 2008 Sep 6, at 13:57, Larry Wall wrote: But basically I think NIL is a mild form of failure anyway, so it's fine with me if () is a form of failure that is smart enough to be I'm thinking () is the non-scalar (list, array, capture, maybe hash) version of undef, which acts like a value unless you have warnings turned on; and undef is managed as a kind of unthrown exception already, thus so should (). -- 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 universityKF8NH
[svn:perl6-synopsis] r14580 - doc/trunk/design/syn
Author: larry Date: Sat Sep 6 21:22:00 2008 New Revision: 14580 Modified: doc/trunk/design/syn/S03.pod Log: where as Junctional infix resembling , but with order guaranteed Modified: doc/trunk/design/syn/S03.pod == --- doc/trunk/design/syn/S03.pod(original) +++ doc/trunk/design/syn/S03.podSat Sep 6 21:22:00 2008 @@ -12,9 +12,9 @@ Maintainer: Larry Wall [EMAIL PROTECTED] Date: 8 Mar 2004 - Last Modified: 21 Jun 2008 + Last Modified: 6 Jun 2008 Number: 3 - Version: 137 + Version: 138 =head1 Overview @@ -38,7 +38,7 @@ L Additive + - +| +^ ~| ~^ ?| ?^ L Replication x xx X Concatenation ~ -X Junctive and +X Junctive and where X Junctive or | ^ L Named unary sleep abs sin N Nonchaining infix but does = leg cmp .. ..^ ^.. ^..^ @@ -947,6 +947,23 @@ $a $b $c ... +=item * + +C infix:where , sequential junctional and operator + +EXPR where EXPR where EXPR ... + +Can be used to construct ANDed patterns with the same semantics as +C infix: , but with left-to-right evaluation guaranteed, for use +in guarded patterns: + +$target ~~ MyType where .mytest1 where .mytest2 + +This is useful when later tests might throw exceptions if earlier +tests don't pass. This cannot be guaranteed by: + +$target ~~ MyType .mytest1 .mytest2 + =back =head2 Junctive or (any) precedence
