[svn:perl6-synopsis] r14356 - doc/trunk/design/syn
Author: larry
Date: Wed Mar 28 12:46:50 2007
New Revision: 14356
Modified:
doc/trunk/design/syn/S04.pod
doc/trunk/design/syn/S06.pod
Log:
Simplified - binding not to autoalias $_ to first arg, per TheDamian++
Also clarified why when must always break from immediately surrounding block.
Juerd++'s double-pointy block now allowed as convenient way to make all
parameters default to rw.
Implicit $_ arg now defined in terms of -
Modified: doc/trunk/design/syn/S04.pod
==
--- doc/trunk/design/syn/S04.pod(original)
+++ doc/trunk/design/syn/S04.podWed Mar 28 12:46:50 2007
@@ -12,9 +12,9 @@
Maintainer: Larry Wall [EMAIL PROTECTED]
Date: 19 Aug 2004
- Last Modified: 12 Mar 2007
+ Last Modified: 28 Mar 2007
Number: 4
- Version: 54
+ Version: 55
This document summarizes Apocalypse 4, which covers the block and
statement syntax of Perl.
@@ -390,8 +390,23 @@
for =$*ARGS {...}
-Parameters are by default readonly within the block. You can
-declare a parameter read/write by including the Cis rw trait.
+Arguments bound to the formal parameters of a pointy block are by
+default readonly within the block. You can declare a parameter
+read/write by including the Cis rw trait. The following treats
+every other value in C@values as modifiable:
+
+for @values - $even is rw, $odd { ... }
+
+In the case where you want all your parameters to default to Crw,
+you may use the visually suggestive double-ended arrow to indicate that
+values flow both ways:
+
+for @values - $even, $odd { ... }
+
+This is equivalent to
+
+for @values - $even is rw, $odd is rw { ... }
+
If you rely on C$_ as the implicit parameter to a block,
then C$_ is considered read/write by default. That is,
the construct:
@@ -400,10 +415,9 @@
is actually short for:
-for @foo - $_ is rw {...}
+for @foo - $_ {...}
-so you can modify the current list element in that case. However,
-any time you specify the arguments, they default to read only.
+so you can modify the current list element in that case.
When used as statement modifiers, Cfor and Cgiven use a private
instance of C$_ for the left side of the statement. The outer C$_
@@ -551,16 +565,20 @@
}
The current topic is always aliased to the special variable C$_.
-The Cgiven block is just one way to set the current topic, but a
-switch statement can be any block that sets C$_, including a Cfor
-loop (in which the first loop parameter is the topic) or the body
-of a method (if you have declared the invocant as C$_). So switching
-behavior is actually caused by the Cwhen statements in the block,
-not by the nature of the block itself. A Cwhen statement implicitly
-does a smart match between the current topic (C$_) and the argument
-of the Cwhen. If the smart match succeeds, Cwhen's associated block
-is executed, and the surrounding block is automatically broken out of.
-The value of the inner block is returned as the value of the outer block.
+The Cgiven block is just one way to set the current topic, but
+a switch statement can be any block that sets C$_, including a
+Cfor loop (assuming one of its loop variables is bound to C$_)
+or the body of a method (if you have declared the invocant as C$_).
+So switching behavior is actually caused by the Cwhen statements in
+the block, not by the nature of the block itself. A Cwhen statement
+implicitly does a smart match between the current topic (C$_) and
+the argument of the Cwhen. If the smart match succeeds, Cwhen's
+associated block is executed, and the immediatly surrounding block
+is automatically broken out of. (If that is not the block you wish
+to leave, you must use the CLABEL.leave method to be more specific,
+since the compiler may find it difficult to guess which surrounding
+construct last set C$_ as the topic.) The value of the inner block
+is returned as the value of the outer block.
If the smart match fails, control passes to the next statement
normally, which may or may not be a Cwhen statement. Since Cwhen
@@ -583,14 +601,12 @@
fall off the last Cwhen into ordinary code. But use of a Cdefault
block is good documentation.
-If you use a Cfor loop with a named parameter, the parameter is
-also aliased to C$_ so that it can function as the topic of any
-Cwhen statements within the loop. If you use a Cfor statement
-with multiple parameters, only the first parameter is aliased to C$_
-as the topic.
+If you use a Cfor loop with a parameter named C$_ (either
+explicitly or implicitly), that parameter can function as the topic
+of any Cwhen statements within the loop.
You can explicitly break out of a Cwhen block (and its surrounding
-switch) early using the Cbreak verb. You can explicitly break out
+block) early using the Cbreak verb. You can explicitly break out
of a Cwhen block and go to the next statement by using Ccontinue.
(Note that, unlike C's idea of
[svn:perl6-synopsis] r14357 - doc/trunk/design/syn
Author: larry Date: Wed Mar 28 13:17:43 2007 New Revision: 14357 Modified: doc/trunk/design/syn/S04.pod Log: Tweaked when/break to leave innermost block with formal $_ (also TheDamian++) Modified: doc/trunk/design/syn/S04.pod == --- doc/trunk/design/syn/S04.pod(original) +++ doc/trunk/design/syn/S04.podWed Mar 28 13:17:43 2007 @@ -14,7 +14,7 @@ Date: 19 Aug 2004 Last Modified: 28 Mar 2007 Number: 4 - Version: 55 + Version: 56 This document summarizes Apocalypse 4, which covers the block and statement syntax of Perl. @@ -573,12 +573,14 @@ the block, not by the nature of the block itself. A Cwhen statement implicitly does a smart match between the current topic (C$_) and the argument of the Cwhen. If the smart match succeeds, Cwhen's -associated block is executed, and the immediatly surrounding block -is automatically broken out of. (If that is not the block you wish -to leave, you must use the CLABEL.leave method to be more specific, -since the compiler may find it difficult to guess which surrounding -construct last set C$_ as the topic.) The value of the inner block -is returned as the value of the outer block. +associated block is executed, and the innermost surrounding block +that has C$_ as one of its formal parameters (either explicit +or implicit) is automatically broken out of. (If that is not the +block you wish to leave, you must use the CLABEL.leave method to +be more specific, since the compiler may find it difficult to guess +which surrounding construct was intended as the actual topicalizer.) +The value of the inner block is returned as the value of the outer +block. If the smart match fails, control passes to the next statement normally, which may or may not be a Cwhen statement. Since Cwhen @@ -605,8 +607,12 @@ explicitly or implicitly), that parameter can function as the topic of any Cwhen statements within the loop. -You can explicitly break out of a Cwhen block (and its surrounding -block) early using the Cbreak verb. You can explicitly break out +You can explicitly break out of a Cwhen block (and its surrounding topicalizer +block) early using the Cbreak verb. More precidely, it leaves the +innermost block outside the Cwhen that uses C$_ as one of its formal +parameters, either explicitly or implicitly. + +You can explicitly break out of a Cwhen block and go to the next statement by using Ccontinue. (Note that, unlike C's idea of falling through, subsequent Cwhen conditions are evaluated. To jump into the next Cwhen block you
Re: [svn:perl6-synopsis] r14357 - doc/trunk/design/syn
[EMAIL PROTECTED] skribis 2007-03-28 13:17 (-0700): +block) early using the Cbreak verb. More precidely, it leaves the precisely? -- korajn salutojn, juerd waalboer: perl hacker [EMAIL PROTECTED] http://juerd.nl/sig convolution: ict solutions and consultancy [EMAIL PROTECTED] Ik vertrouw stemcomputers niet. Zie http://www.wijvertrouwenstemcomputersniet.nl/.
[svn:perl6-synopsis] r14358 - doc/trunk/design/syn
Author: larry Date: Wed Mar 28 14:42:41 2007 New Revision: 14358 Modified: doc/trunk/design/syn/S04.pod Log: typo from Juerd++ Modified: doc/trunk/design/syn/S04.pod == --- doc/trunk/design/syn/S04.pod(original) +++ doc/trunk/design/syn/S04.podWed Mar 28 14:42:41 2007 @@ -608,7 +608,7 @@ of any Cwhen statements within the loop. You can explicitly break out of a Cwhen block (and its surrounding topicalizer -block) early using the Cbreak verb. More precidely, it leaves the +block) early using the Cbreak verb. More precisely, it leaves the innermost block outside the Cwhen that uses C$_ as one of its formal parameters, either explicitly or implicitly.
[svn:perl6-synopsis] r14359 - doc/trunk/design/syn
Author: larry Date: Wed Mar 28 19:28:28 2007 New Revision: 14359 Modified: doc/trunk/design/syn/S09.pod Log: User-definable array indexing hammered out by TheDamian++ and Dataweaver++ Modified: doc/trunk/design/syn/S09.pod == --- doc/trunk/design/syn/S09.pod(original) +++ doc/trunk/design/syn/S09.podWed Mar 28 19:28:28 2007 @@ -12,9 +12,9 @@ Maintainer: Larry Wall [EMAIL PROTECTED] Date: 13 Sep 2004 - Last Modified: 14 Mar 2007 + Last Modified: 28 Mar 2007 Number: 9 - Version: 18 + Version: 19 =head1 Overview @@ -146,6 +146,87 @@ buffer type. The unpacking is performed by coercion of such a buffer type back to the type of the compact struct. +=head1 Standard array indexing + +Standard array indices are specified using square brackets. Standard +indices always start at zero in each dimension of the array (see +LMultidimensional arrays), and are always contiguous: + +@dwarves[0] = Happy; # The 1st dwarf +@dwarves[6] = Doc; # The 7th dwarf + +@seasons[0] = Spring; # The 1st season +@seasons[2] = Autumn|Fall; # The 3rd season + + +=head1 Fixed-size arrays + +A basic array declaration like: + +my @array; + +declares a one-dimensional array of indeterminate length. Such arrays +are autoextending. For many purposes, though, it's useful to define +array types of a particular size and shape that, instead of +autoextending, fail if you try to access outside their +declared dimensionality. Such arrays tend to be faster to allocate and +access as well. (The language must, however, continue to protect you +against overflow--these days, that's not just a reliability issue, but +also a security issue.) + +To declare an array of fixed size, specify its maximum number of elements +in square brackets immediately after its name: + +my @dwarves[7]; # Valid indices are 0..6 + +my @seasons[4]; # Valid indices are 0..4 + +No intervening whitespace is permitted between the name and the size +specification, but unspace is allowed: + +my @values[10]; # Okay +my @keys [10]; # Error +my @keys\ [10]; # Okay + +Note that the square brackets are a compile-time declarator, not a run-time +operator, so you can't use the dotted form either: + +my @values.[10]; # Error +my @keys\ .[10]; # Error + +Attempting to access an index outside a array's defined range will fail: + +@dwarves[7] = 'Sneaky'; # Fails with invalid index exception + +It's also possible to explicitly specify a normal autoextending array: + +my @vices[*]; # Length is: whatever + # Valid indices are 0..* + +=head1 Typed arrays + +The type of value stored in each element of the array (normally CAny) +can be explicitly specified too, as an external Cof type: + +my num @nums; # Each element stores a native number +my @nums of num; # Same + +my Book @library[1_000_000]; # Each element stores a Book object +my @library[1_000_000] of Book; # Same + +Alternatively, the element storage type may be specified as part of the +dimension specifier (much like a subroutine definition): + +my @nums[--num]; + +my @library[1_000_000 -- Book]; + +Arrays may also be defined with a mixture of fixed and autoextending +dimensions: + +my @calendar[12;*;24]; # Month dimension unlimited + + =head1 Compact arrays In declarations of the form: @@ -166,6 +247,10 @@ hard to make these elements look like objects when you treat them like objects--this is called autoboxing.) +Such arrays are autoextending just like ordinary Perl arrays +(at the price of occasionally copying the block of data to another +memory location, or using a tree structure). + A compact array is for most purposes interchangeable with the corresponding buffer type. For example, apart from the sigil, these are equivalent declarations: @@ -204,33 +289,45 @@ known encoding. Otherwise you must encode them explicitly from the higher-level abstraction into some buffer type.) + =head1 Multidimensional arrays -The declarations above declare one-dimensional arrays of indeterminate -length. Such arrays are autoextending just like ordinary Perl arrays -(at the price of occasionally copying the block of data to another -memory location, or using a tree structure). For many purposes, -though, it's useful to define array types of a particular size and -shape that, instead of autoextending, throw an exception if you try -to access outside their declared dimensionality. Such arrays tend -to be faster to allocate and access as well. (The language must, -however, continue to protect you against overflow--these days, that's -not just a reliability issue, but also a security issue.) +Perl 6 arrays are not restricted to being
[svn:perl6-synopsis] r14359 - doc/trunk/design/syn
From: [EMAIL PROTECTED] Date: Wed, 28 Mar 2007 19:28:30 -0700 (PDT) Author: larry Date: Wed Mar 28 19:28:28 2007 New Revision: 14359 Modified: doc/trunk/design/syn/S09.pod Log: User-definable array indexing hammered out by TheDamian++ and Dataweaver++ . . . +To declare an array of fixed size, specify its maximum number of elements +in square brackets immediately after its name: + +my @dwarves[7]; # Valid indices are 0..6 + +my @seasons[4]; # Valid indices are 0..4 Huh?? I assume you didn't mean to throw in an extra season . . . -- Bob Rogers http://rgrjr.dyndns.org/
[svn:perl6-synopsis] r14360 - doc/trunk/design/syn
Author: larry Date: Wed Mar 28 23:21:49 2007 New Revision: 14360 Modified: doc/trunk/design/syn/S09.pod Log: Clarifications requested by spinclad++ and Bob Rogers++. Modified: doc/trunk/design/syn/S09.pod == --- doc/trunk/design/syn/S09.pod(original) +++ doc/trunk/design/syn/S09.podWed Mar 28 23:21:49 2007 @@ -179,7 +179,7 @@ my @dwarves[7]; # Valid indices are 0..6 -my @seasons[4]; # Valid indices are 0..4 +my @seasons[4]; # Valid indices are 0..3 No intervening whitespace is permitted between the name and the size specification, but unspace is allowed: @@ -222,9 +222,10 @@ my @library[1_000_000 -- Book]; Arrays may also be defined with a mixture of fixed and autoextending -dimensions: +dimensions. There are always 12 months in a year and 24 hours in a day, +but the number of days in the month can vary: -my @calendar[12;*;24]; # Month dimension unlimited +my @calendar[12;*;24]; # day-of-month dimension unlimited/ragged =head1 Compact arrays
[svn:perl6-synopsis] r14361 - doc/trunk/design/syn
Author: larry Date: Wed Mar 28 23:32:40 2007 New Revision: 14361 Modified: doc/trunk/design/syn/S09.pod Log: Clarification suggested by gaal++ Modified: doc/trunk/design/syn/S09.pod == --- doc/trunk/design/syn/S09.pod(original) +++ doc/trunk/design/syn/S09.podWed Mar 28 23:32:40 2007 @@ -222,8 +222,9 @@ my @library[1_000_000 -- Book]; Arrays may also be defined with a mixture of fixed and autoextending -dimensions. There are always 12 months in a year and 24 hours in a day, -but the number of days in the month can vary: +dimensions (see below). For example, there are always 12 months in +a year and 24 hours in a day, but the number of days in the month +can vary: my @calendar[12;*;24]; # day-of-month dimension unlimited/ragged
