Author: lwall
Date: 2009-02-20 22:59:01 +0100 (Fri, 20 Feb 2009)
New Revision: 25464
Modified:
docs/Perl6/Spec/S02-bits.pod
Log:
define Instant and Duration as core types representing atomic time
Modified: docs/Perl6/Spec/S02-bits.pod
===================================================================
--- docs/Perl6/Spec/S02-bits.pod 2009-02-20 21:56:48 UTC (rev 25463)
+++ docs/Perl6/Spec/S02-bits.pod 2009-02-20 21:59:01 UTC (rev 25464)
@@ -12,9 +12,9 @@
Maintainer: Larry Wall <la...@wall.org>
Date: 10 Aug 2004
- Last Modified: 6 Feb 2009
+ Last Modified: 20 Feb 2009
Number: 2
- Version: 152
+ Version: 153
This document summarizes Apocalypse 2, which covers small-scale
lexical items and typological issues. (These Synopses also contain
@@ -972,6 +972,8 @@
Signature Function parameters (left-hand side of a binding)
Capture Function call arguments (right-hand side of a binding)
Blob An undifferentiated mass of bits
+ Instant A point on the continuous atomic timeline (TAI)
+ Duration The differences between two Instants
Insofar as Lists are lazy, they're really only partially immutable, in
the sense that the past is fixed but the future is not. The portion of
@@ -983,6 +985,21 @@
the degree of laziness/eagerness desired in context. The iterator
API is described in S07.
+C<Instant>s and C<Duration>s are measured in atomic seconds with
+fractions. Notionally they are real numbers which may be implemented
+in either C<Num> or C<Rat> types. (Fixed-point implementations are
+strongly discouraged.) Interfaces that take C<Duration> arguments,
+such as sleep(), may also take C<Num> arguments, but C<Instant>
+arguments must be explicitly created via any of various culturally
+aware time specification APIs that, by and large, are outside the
+CORE of Perl 6, with the possible exception of a constructor taking a
+native TAI value. In numeric context a C<Duration> happily returns a
+C<Num> representing seconds. If pressed for a number, an C<Instant>
+will return the length of time in atomic seconds from the TAI epoch,
+but it will be unhappy about it. Systems which cannot provide
+a steady time base, such as POSIX systems, will simply have to make
+their best guess as to the correct atomic time.
+
=head2 Mutable types
Objects with these types have distinct C<.WHICH> values that do not change
