NAME
Muldis::D::Ext::Temporal - Muldis D extension for temporal data types and operators
VERSION
This document is Muldis::D::Ext::Temporal version 0.143.0.
PREFACE
This document is part of the Muldis D language specification, whose root document is Muldis::D; you should read that root document before you read this one, which provides subservient details.
DESCRIPTION
Muldis D has a mandatory core set of system-defined (eternally available) entities, which is referred to as the Muldis D core or the core; they are the minimal entities that all Muldis D implementations need to provide; they are mutually self-describing and are either used to bootstrap the language or they constitute a reasonable minimum level of functionality for a practically useable industrial-strength (and fully TTM-conforming) programming language; any entities outside the core, called Muldis D extensions, are non-mandatory and are defined in terms of the core or each other, but the reverse isn't true.
This current Temporal document describes the system-defined Muldis D Temporal Extension, which consists of temporal data types and operators. To be specific, the Muldis D Temporal Extension only describes the most generic temporal-concerning mixin types, plus the most generic virtual routines to use with them; it does not define any types that compose these mixins, or routines that implement those virtuals. It is expected, considering the complexity of temporals, that in the general case any temporal types and routines that would actually be used would be either user-defined, or implementation-defined, or both, or some other standard Muldis D extensions would provide them; the latter don't exist yet.
See also the separately-distributed Muldis::D::Manual::TemporalExtras document, which provides complete examples of temporal types that could compose this extension's mixins, and of routines that could implement its virtual routines.
This current document does not describe the polymorphic operators that all types, or some types including core types, have defined over them; said operators are defined once for all types in Muldis::D::Core.
TYPE SUMMARY
Following are all the data types described in this document, which are all mixin types, arranged in a type graph according to their proper sub|supertype relationships; currently there are no system-defined types that compose them:
sys.std.Core.Type.Universal
sys.std.Temporal.Type.Instant
sys.std.Temporal.Type.DurationTEMPORAL MIXIN DATA TYPES
sys.std.Temporal.Type.Instant
The Instant type is a mixin (union) type that is intended to be explicitly composed by every other type where each of the values of that type is considered to be an instant, which is a distinct point on some timeline. Types that compose Instant can vary greatly with respect to either what timeline/calendar provides the context for interpreting them, or to what their granularity is. Common examples of an instant are a datetime or a date or a time. The cardinality of Instant is infinity. The Instant type is not itself ordered, but often a type which composes Duration is also ordered. The Instant type is intended to have exactly the same meaning as the same-named type of Perl 6 (see http://perlcabal.org/syn/S02.html for details). The default value of Instant is implementation-defined.
sys.std.Temporal.Type.Duration
The Duration type is a mixin (union) type that is intended to be explicitly composed by every other type where each of the values of that type is considered to be a duration, which is a single amount of time that is generally specified in terms of the same units as an instant, and it is generally interpreted with respect to a timeline or calendar. A Duration is, by definition, the result of taking the difference of 2 Instant. A Duration is not fixed to any points on a timeline, simply dealing with a quantity. If you want to represent an interval of time that is anchored to a timeline, then canonically you do this in terms of a composite type having two Instant attributes representing the endpoints; either an sp_interval_of.Instant or an mp_interval_of.Instant. The cardinality of Duration is infinity. The Duration type is not itself ordered, but often a type which composes Duration is also ordered. The Duration type is intended to have exactly the same meaning as the same-named type of Perl 6. The default value of Duration is implementation-defined.
VIRTUAL FUNCTIONS FOR THE INSTANT MIXIN TYPE
sys.std.Temporal.Instant.diff
function diff (Duration <-- minuend@ : Instant, subtrahend@ : Instant) {...}
This virtual function results in the duration-typed difference when its instant-typed subtrahend argument is subtracted from its instant-typed minuend argument. The result is the amount of time between the 2 arguments, which may be positive or negative depending on which argument was earlier.
sys.std.Temporal.Instant.abs_diff
function abs_diff (Duration <-- topic@ : Instant, other@ : Instant) {...}
This virtual symmetric function results in the absolute difference between its 2 arguments. The result is the amount of time between the 2 arguments, which is always non-negative.
sys.std.Temporal.Instant.later
function later (Instant <-- instant@ : Instant, duration@ : Duration) {...}
This virtual function results in the instant that is later than its instant argument by the amount of time in the duration argument.
sys.std.Temporal.Instant.earlier
function earlier (Instant <-- instant@ : Instant, duration@ : Duration) {...}
This virtual function results in the instant that is earlier than its instant argument by the amount of time in the duration argument.
VIRTUAL FUNCTIONS FOR THE DURATION MIXIN TYPE
sys.std.Temporal.Duration.abs
function abs (Duration <-- topic@ : Duration) {...}
This virtual function results in the absolute value of its argument.
sys.std.Temporal.Duration.sum
function sum (Duration <-- topic@ : bag_of.Duration) {...}
This virtual function results in the sum of the N element values of its argument; it is a reduction operator that recursively takes each pair of input values and adds (which is both commutative and associative) them together until just one is left, which is the result. Conceptually, if topic has zero values, then sum results in the duration zero, which is the identity value for addition; however, while each implementing function of sum could actually result in a type-specific value of zero, this virtual function itself will instead fail when topic has zero values, because then it would lack the necessary type information to know which type-specific implementing function to dispatch to.
sys.std.Temporal.Duration.diff
function diff (Duration <-- minuend@ : Duration, subtrahend@ : Duration) {...}
This virtual function results in the difference when its subtrahend argument is subtracted from its minuend argument.
sys.std.Temporal.Duration.abs_diff
function abs_diff (Duration <-- topic@ : Duration, other@ : Duration) {...}
This virtual symmetric function results in the absolute difference between its 2 arguments.
VIRTUAL SYSTEM-SERVICES FOR CURRENT DATES AND TIMES
sys.std.Temporal.Instant.fetch_curr_instant
system-service fetch_curr_instant (&target@ : Instant) [...]
This virtual system-service routine will update the variable supplied as its target argument so that it holds the value of the current instant as taken from the implementation's system clock or the time server it uses. The implementing system-service which this dispatches to is determined by the the type of the value that target has at the moment that fetch_curr_instant is invoked; typically that value is the default value of the declared type of the invoker variable that target's argument; this routine might fail if said declared type isn't a subset of Instant.
SEE ALSO
Go to Muldis::D for the majority of distribution-internal references, and Muldis::D::SeeAlso for the majority of distribution-external references.
AUTHOR
Darren Duncan (darren@DarrenDuncan.net)
LICENSE AND COPYRIGHT
This file is part of the formal specification of the Muldis D language.
Muldis D is Copyright © 2002-2010, Muldis Data Systems, Inc.
See the LICENSE AND COPYRIGHT of Muldis::D for details.
TRADEMARK POLICY
The TRADEMARK POLICY in Muldis::D applies to this file too.
ACKNOWLEDGEMENTS
The ACKNOWLEDGEMENTS in Muldis::D apply to this file too.