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Vitor Santos Costa
2018-05-10 13:11:56 +01:00
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docs/md/attributes.md
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@@ -1,8 +1,9 @@
Attributed Variables and Co-Routining {#AttributedVariables}
====================================
@defgroup AttributedVariables Attributed Variables and Co-Routining
@ingroup extensions
@{
YAP supports attributed variables, originally developed at OFAI by
Christian Holzbaur. Attributes are a means of declaring that an
@@ -27,9 +28,8 @@ work with. Most packages included in YAP that use attributed
variables, such as CHR, CLP(FD), and CLP(QR), rely on the SWI-Prolog
awi interface.
[TOC]
@defgroup SICS_attributes SICStus Style attribute declarations.
## SICStus Style attribute declarations. {#SICS_attributes}
The YAP library `atts` implements attribute variables in the style of
SICStus Prolog. Attributed variables work as follows:
@@ -82,9 +82,10 @@ mechanism is used for this purpose.
The attribute manipulation predicates always work as follows:
+ The first argument is the unbound variable associated with
+ The first argument is the unbound variable associated with
attributes,
+ The second argument is a list of attributes. Each attribute will
+ The second argument is a list of attributes. Each attribute will
be a Prolog term or a constant, prefixed with the <tt>+</tt> and <tt>-</tt> unary
operators. The prefix <tt>+</tt> may be dropped for convenience.
@@ -99,9 +100,9 @@ attempting to unify an attributed variable which might have attributes
in some _Module_.
Attributes are usually presented as goals. The following routines are
used by built-in predicates such as call_residue/2 and by the
Prolog top-level to display attributes:
At execution conclusion, attributes still unsatisfied are presented as
goals. The following routines are used by built-in predicates such as
call_residue/2 and by the Prolog top-level to display attributes:
Constraint solvers must be able to project a set of constraints to a set
@@ -269,12 +270,11 @@ variables only. More complicated interactions are likely to be found
in more sophisticated solvers. The corresponding
verify_attributes/3 predicates would typically refer to the
attributes from other known solvers/modules via the module prefix in
Module:get_atts/2`.
Module:get_atts/2.
@}
@{
#### hProlog and SWI-Prolog style Attribute Declarations {#New_Style_Attribute_Declarations}
hProlog and SWI-Prolog style Attribute Declarations {#New_Style_Attribute_Declarations}
------------------------------------------------
The following documentation is taken from the SWI-Prolog manual.
@@ -286,24 +286,28 @@ Module:get_atts/2`.
executed in this module. The example below realises a very simple and
incomplete finite domain reasoner.
~~~~~
:- module(domain,
[ domain/2 % Var, ?Domain %
]).
:- use_module(library(ordsets)).
~~~~~
:- module(domain,
[ domain/2 % Var, ?Domain %
]).
:- use_module(library(ordsets)).
domain(X, Dom) :-
var(Dom), !,
get_attr(X, domain, Dom).
domain(X, List) :-
list_to_ord_set(List, Domain),
put_attr(Y, domain, Domain),
X = Y.
domain(X, Dom) :-
var(Dom), !,
get_attr(X, domain, Dom).
domain(X, List) :-
list_to_ord_set(List, Domain),
v put_attr(Y, domain, Domain),
X = Y.
~~~~~
% An attributed variable with attribute value Domain has been %
% assigned the value Y %
The next predicate is called *after* _X_, the attributed variable with attribute value _Domain_ has been
assigned the value Y.
attr_unify_hook(Domain, Y) :-
~~~~~
attr_unify_hook(Domain, Y) :-
( get_attr(Y, domain, Dom2)
-> ord_intersection(Domain, Dom2, NewDomain),
( NewDomain == []
@@ -316,15 +320,17 @@ v put_attr(Y, domain, Domain),
-> put_attr( Y, domain, Domain )
; ord_memberchk(Y, Domain)
).
~~~~~
% Translate attributes from this module to residual goals %
The user defined attribute_goals/1 attributes from this module to residual goals
attribute_goals(X) -->
~~~~~
attribute_goals(X) -->
{ get_attr(X, domain, List) },
[domain(X, List)].
~~~~~
~~~~~
Before explaining the code we give some example queries:
Before explaining the code in detail we give some example queries:
The predicate `domain/2` fetches (first clause) or assigns
(second clause) the variable a <em>domain</em>, a set of values it can
@@ -342,11 +348,8 @@ v put_attr(Y, domain, Domain),
remaining attributes to user-readable goals that, when executed, reinstate
these attributes.
@}
@{
#### Co-routining {#CohYroutining}
Co-routining {#CohYroutining}
------------
Prolog uses a simple left-to-right flow of control. It is sometimes
convenient to change this control so that goals will only execute when
@@ -359,31 +362,27 @@ attributed variables to implement co-routining.
Two declarations are supported:
+ block/1
The argument to `block/1` is a condition on a goal or a conjunction
of conditions, with each element separated by commas. Each condition is
of the form `predname( _C1_,..., _CN_)`, where _N_ is the
arity of the goal, and each _CI_ is of the form `-`, if the
argument must suspend until the first such variable is bound, or
`?`, otherwise.
+ block/1
The argument to `block/1` is a condition on a goal or a conjunction
of conditions, with each element separated by commas. Each condition is
of the form `predname( _C1_,..., _CN_)`, where _N_ is the
arity of the goal, and each _CI_ is of the form `-`, if the
argument must suspend until the first such variable is bound, or
`?`, otherwise.
+ wait/1
The argument to `wait/1` is a predicate descriptor or a conjunction
of these predicates. These predicates will suspend until their first
argument is bound.
+ wait/1
The argument to `wait/1` is a predicate descriptor or a conjunction
of these predicates. These predicates will suspend until their first
argument is bound.
The following primitives can be used:
- freeze/2
- freeze/2
- dif/2
- dif/2
- when/2
- when/2
- frozen/2
- frozen/2
@}
@}