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29
CLPBN/clpbn/utils.yap
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@ -37,10 +37,10 @@ clpbn_not_var_member([V1|Vs], V) :- V1 \== V,
clpbn_not_var_member(Vs, V).
sort_vars_by_key(AVars, SortedAVars, Keys) :-
sort_vars_by_key(AVars, SortedAVars, UnifiableVars) :-
get_keys(AVars, KeysVars),
keysort(KeysVars, KVars),
merge_same_key(KVars, SortedAVars, Keys).
merge_same_key(KVars, SortedAVars, [], UnifiableVars).
get_keys([], []).
get_keys([V|AVars], [K-V|KeysVars]) :-
@ -49,15 +49,24 @@ get_keys([V|AVars], [K-V|KeysVars]) :-
get_keys([_|AVars], KeysVars) :- % may be non-CLPBN vars.
get_keys(AVars, KeysVars).
merge_same_key([], [], []).
merge_same_key([K1-V1|KVs], [V1|Vs], [K1|Ks]) :-
eat_same_key(KVs,K1,V1,RKVs),
merge_same_key(RKVs, Vs, Ks).
eat_same_key([K-V|KVs],K,V,RKVs) :- !,
eat_same_key(KVs,K,V,RKVs).
eat_same_key(KVs,_,_,KVs).
merge_same_key([], [], _, []).
merge_same_key([K1-V1,K2-V2|Vs], SortedAVars, Ks, UnifiableVars) :-
K1 == K2, !, V1 = V2,
merge_same_key([K1-V1|Vs], SortedAVars, Ks, UnifiableVars).
merge_same_key([K1-V1,K2-V2|Vs], [V1|SortedAVars], Ks, [K1|UnifiableVars]) :-
(in_keys(K1, Ks) ; \+ \+ K1 == K2), !,
add_to_keys(K1, Ks, NKs),
merge_same_key([K2-V2|Vs], SortedAVars, NKs, UnifiableVars).
merge_same_key([K-V|Vs], [V|SortedAVars], Ks, UnifiableVars) :-
add_to_keys(K, Ks, NKs),
merge_same_key(Vs, SortedAVars, NKs, UnifiableVars).
in_keys(K1,[K|_]) :- \+ \+ K1 = K, !.
in_keys(K1,[_|Ks]) :-
in_keys(K1,Ks).
add_to_keys(K1, Ks, Ks) :- ground(K1), !.
add_to_keys(K1, Ks, [K1|Ks]).
sort_vars_by_key_and_parents(AVars, SortedAVars, UnifiableVars) :-
get_keys_and_parents(AVars, KeysVars),

2
CLPBN/clpbn/vel.yap
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@ -297,7 +297,7 @@ divide_by_sum([P|Ps0],Sum,[PN|Ps]) :-
% what is actually output
%
attribute_goal(V, G) :-
get_atts(V, [posterior(Vs,Vals,Ps,AllDiffs)]), !,
get_atts(V, [posterior(Vs,Vals,Ps,AllDiffs)]),
massage_out(Vs, Vals, Ps, G, AllDiffs, V).
massage_out([], Ev, _, V=Ev, _, V) :- !.

11
Makefile.in
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@ -184,6 +184,9 @@ PL_SOURCES= \
$(srcdir)/pl/utils.yap \
$(srcdir)/pl/yapor.yap $(srcdir)/pl/yio.yap
YAPDOCS=$(srcdir)/docs/yap.tex $(srcdir)/docs/chr.tex \
$(srcdir)/docs/clpr.tex $(srcdir)/docs/swi.tex
ENGINE_OBJECTS = \
agc.o absmi.o adtdefs.o alloc.o amasm.o analyst.o arrays.o \
arith0.o arith1.o arith2.o attvar.o bb.o \
@ -616,7 +619,7 @@ install_info:
info: yap.info
yap.info: $(srcdir)/docs/yap.tex
yap.info: $(YAPDOCS)
$(MAKEINFO) $(srcdir)/docs/yap.tex
html: yap.html
@ -626,17 +629,17 @@ yap.html: $(srcdir)/docs/yap.tex
dvi: yap.dvi
yap.dvi: $(srcdir)/docs/yap.tex
yap.dvi: $(YAPDOCS)
$(TEXI2DVI) $(srcdir)/docs/yap.tex
ps: yap.ps
yap.ps: $(srcdir)/docs/yap.dvi
yap.ps: $(YAPDOCS)
dvips -o yap.ps $(srcdir)/docs/yap
pdf: yap.pdf
yap.pdf: $(srcdir)/docs/yap.tex
yap.pdf: $(YAPDOCS)
$(TEXI2PDF) $(srcdir)/docs/yap.tex
clean_docs:

2
changes-5.1.html
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@ -16,6 +16,8 @@
<h2>Yap-5.1.0:</h2>
<ul>
<li> NEW: update documentation to support new CLP(R) and CHR packages. </li>
<li> FIXED: regression in clpbn/utils.yap. </li>
<li> NEW: put_attrs/2. </li>
<li> FIXED: don't install CLP unless coroutining && rational trees are
active. </li>

597
docs/chr.tex Normal file
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@ -0,0 +1,597 @@
@chapter CHR: Constraint Handling Rules
@c \label{sec:chr}
This chapter is written by Tom Schrijvers, K.U. Leuven for the hProlog
system. Adjusted by Jan Wielemaker to fit the SWI-Prolog documentation
infrastructure and remove hProlog specific references.
The CHR system of SWI-Prolog is the K.U.Leuven CHR system. The runtime
environment is written by Christian Holzbaur and Tom Schrijvers while the
compiler is written by Tom Schrijvers. Both are integrated with SWI-Prolog
and licenced under compatible conditions with permission from the authors.
The main reference for SWI-Prolog's CHR system is:
@itemize
@item T. Schrijvers, and B. Demoen, @emph{The K.U.Leuven CHR System: Implementation
and Application}, First Workshop on Constraint Handling Rules: Selected
Contributions (Fruwirth, T. and Meister, M., eds.), pp. 1--5, 2004.
@end itemize
@node CHR Introduction, CHR Syntax and Semantics, , CHR
@section Introduction
@c =====================
Constraint Handling Rules (CHR) is a committed-choice bottom-up language
embedded in Prolog. It is designed for writing constraint solvers and is
particularily useful for providing application-specific constraints.
It has been used in many kinds of applications, like scheduling,
model checking, abduction, type checking among many others.
CHR has previously been implemented in other Prolog systems (SICStus,
Eclipse, Yap), Haskell and Java. This CHR system is based on the
compilation scheme and runtime environment of CHR in SICStus.
In this documentation we restrict ourselves to giving a short overview
of CHR in general and mainly focus on elements specific to this
implementation. For a more thorough review of CHR we refer the reader to
[Freuhwirth:98]. More background on CHR can be found at the CHR web site.
@c \secref{SyntaxAndSemantics} we present the syntax of CHR in Prolog and
@c explain informally its operational semantics. Next, \secref{practical}
@c deals with practical issues of writing and compiling hProlog programs
@c containing CHR. \Secref{debugging} explains the currently primitive CHR
@c debugging facilities. \Secref{predicates} provides a few useful predicates
@c to inspect the constraint store and \secref{examples} illustrates CHR with
@c two example programs. In \secref{sicstus-chr} some compatibility issues with
@c SICStus CHR are listed. Finally, \secref{guidelines} concludes with a few
@c practical guidelines for using CHR.
@node CHR Syntax and Semantics, CHR in YAP Programs, CHR Introduction, CHR
@section Syntax and Semantics
@c \label{sec:SyntaxAndSemantics}
@c=============================
@subsection Syntax
@c -----------------
The syntax of CHR rules in hProlog is the following:
@example
rules --> rule, rules.
rules --> [].
rule --> name, actual_rule, pragma, [atom('.')].
name --> atom, [atom('@')].
name --> [].
actual_rule --> simplification_rule.
actual_rule --> propagation_rule.
actual_rule --> simpagation_rule.
simplification_rule --> constraints, [atom('<=>')], guard, body.
propagation_rule --> constraints, [atom('==>')], guard, body.
simpagation_rule --> constraints, [atom('\')], constraints, [atom('<=>')],
guard, body.
constraints --> constraint, constraint_id.
constraints --> constraint, [atom(',')], constraints.
constraint --> compound_term.
constraint_id --> [].
constraint_id --> [atom('#')], variable.
guard --> [].
guard --> goal, [atom('|')].
body --> goal.
pragma --> [].
pragma --> [atom('pragma')], actual_pragmas.
actual_pragmas --> actual_pragma.
actual_pragmas --> actual_pragma, [atom(',')], actual_pragmas.
actual_pragma --> [atom('passive(')], variable, [atom(')')].
@end example
Additional syntax-related terminology:
@itemize
@item @strong{head:} the constraints in an @code{actual_rule} before
the arrow (either @code{<=>} or @code{==>})
@end itemize
@subsection Semantics
@c --------------------
In this subsection the operational semantics of CHR in Prolog are presented
informally. They do not differ essentially from other CHR systems.
When a constraint is called, it is considered an active constraint and
the system will try to apply the rules to it. Rules are tried and executed
sequentially in the order they are written.
A rule is conceptually tried for an active constraint in the following
way. The active constraint is matched with a constraint in the head of
the rule. If more constraints appear in the head they are looked for
among the suspended constraints, which are called passive constraints in
this context. If the necessary passive constraints can be found and all
match with the head of the rule and the guard of the rule succeeds, then
the rule is committed and the body of the rule executed. If not all the
necessary passive constraint can be found, the matching fails or the
guard fails, then the body is not executed and the process of trying and
executing simply continues with the following rules. If for a rule,
there are multiple constraints in the head, the active constraint will
try the rule sequentially multiple times, each time trying to match with
another constraint.
This process ends either when the active constraint disappears, i.e. it
is removed by some rule, or after the last rule has been processed. In
the latter case the active constraint becomes suspended.
A suspended constraint is eligible as a passive constraint for an active
constraint. The other way it may interact again with the rules, is when
a variable appearing in the constraint becomes bound to either a nonvariable
or another variable involved in one or more constraints. In that case the
constraint is triggered, i.e. it becomes an active constraint and all
the rules are tried.
@unnumberedsubsubsec Rule Types
@c - - - - - - - - - -
There are three different kinds of rules, each with their specific semantics:
@table @code
@item simplification
The simplification rule removes the constraints in its head and calls its body.
@item propagation
The propagation rule calls its body exactly once for the constraints in
its head.
@item simpagation
The simpagation rule removes the constraints in its head after the
@code{\} and then calls its body. It is an optimization of
simplification rules of the form: \[constraints_1, constraints_2 <=>
constraints_1, body \] Namely, in the simpagation form:
@example
constraints1 \ constraints2 <=> body
@end example
@noindent
@var{constraints1}
constraints are not called in the body.
@end table
@unnumberedsubsubsec Rule Names
@c - - - - - - - - - -
Naming a rule is optional and has no semantical meaning. It only functions
as documentation for the programmer.
@unnumberedsubsubsec Pragmas
@c - - - - - - - - -
The semantics of the pragmas are:
@table @option
@item passive(Identifier)
The constraint in the head of a rule @var{Identifier} can only act as a
passive constraint in that rule.
@end table
Additional pragmas may be released in the future.
@unnumberedsubsubsec Options
@c - - - - - - - - -
It is possible to specify options that apply to all the CHR rules in the module.
Options are specified with the @code{option/2} declaration:
@example
option(Option,Value).
@end example
Available options are:
@table @code
@item check_guard_bindings
This option controls whether guards should be checked for illegal
variable bindings or not. Possible values for this option are
@code{on}, to enable the checks, and @code{off}, to disable the
checks.
@item optimize
This is an experimental option controlling the degree of optimization.
Possible values are @code{full}, to enable all available
optimizations, and @code{off} (default), to disable all optimizations.
The default is derived from the SWI-Prolog flag @code{optimise}, where
@code{true} is mapped to @code{full}. Therefore the commandline
option @option{-O} provides full CHR optimization.
If optimization is enabled, debugging should be disabled.
@item debug
This options enables or disables the possibility to debug the CHR code.
Possible values are @code{on} (default) and @code{off}. See
@option{debugging} for more details on debugging. The default is
derived from the prolog flag @code{generate_debug_info}, which
is @code{true} by default. See @option{-nodebug}.
If debugging is enabled, optimization should be disabled.
@item mode
This option specifies the mode for a particular constraint. The
value is a term with functor and arity equal to that of a constraint.
The arguments can be one of @code{-}, @code{+} or @code{?}.
The latter is the default. The meaning is the following:
@table @code
@item -
The corresponding argument of every occurrence
of the constraint is always unbound.
@item +
The corresponding argument of every occurrence
of the constraint is always ground.
@item ?
The corresponding argument of every occurrence
of the constraint can have any instantiation, which may change
over time. This is the default value.
@end table
The declaration is used by the compiler for various optimizations.
Note that it is up to the user the ensure that the mode declaration
is correct with respect to the use of the constraint.
This option may occur once for each constraint.
@item type_declaration
This option specifies the argument types for a particular constraint. The
value is a term with functor and arity equal to that of a constraint.
The arguments can be a user-defined type or one of
the built-in types:
@table @code
@item int
The corresponding argument of every occurrence
of the constraint is an integer number.
@item float
@dots{} a floating point number.
@item number
@dots{} a number.
@item natural
@dots{} a positive integer.
@item any
The corresponding argument of every occurrence
of the constraint can have any type. This is the default value.
@end table
Currently, type declarations are only used to improve certain
optimizations (guard simplification, occurrence subsumption, @dots{}).
@item type_definition
This option defines a new user-defined type which can be used in
type declarations. The value is a term of the form
@code{type(}@var{name}@code{,}@var{list}@code{)}, where
@var{name} is a term and @var{list} is a list of alternatives.
Variables can be used to define generic types. Recursive definitions
are allowed. Examples are
@example
type(bool,[true,false]).
type(complex_number,[float + float * i]).
type(binary_tree(T),[ leaf(T) | node(binary_tree(T),binary_tree(T)) ]).
type(list(T),[ [] | [T | list(T)]).
@end example
@end table
The mode, type_declaration and type_definition options are provided
for backward compatibility. The new syntax is described below.
@node CHR in YAP Programs, CHR Debugging, CHR Syntax and Semantics, CHR
@section CHR in YAP Programs
@c \label{sec:practical}
@c===========================
@subsection Embedding in Prolog Programs
The CHR constraints defined in a particulary @file{chr} file are
associated with a module. The default module is @code{user}. One should
never load different @file{chr} files with the same CHR module name.
@subsection Constraint declaration
Every constraint used in CHR rules has to be declared.
There are two ways to do this. The old style is as follows:
@example
option(type_definition,type(list(T),[ [] , [T|list(T)] ]).
option(mode,foo(+,?)).
option(type_declaration,foo(list(int),float)).
:- constraints foo/2, bar/0.
@end example
The new style is as follows:
@example
:- chr_type list(T) ---> [] ; [T|list(T)].
:- constraints foo(+list(int),?float), bar.
@end example
@subsection Compilation
The SWI-Prolog CHR compiler exploits term_expansion/2 rules to translate
the constraint handling rules to plain Prolog. These rules are loaded
from the library @file{chr}. They are activated if the compiled file
has the @file{chr} extension or after finding a declaration of the
format below.
@example
:- constraints ...
@end example
It is adviced to define CHR rules in a module file, where the module
declaration is immediately followed by including the @file{chr}
library as examplified below:
@example
:- module(zebra, [ zebra/0 ]).
:- use_module(library(chr)).
:- constraints ...
@end example
Using this style CHR rules can be defined in ordinary Prolog
@file{pl} files and the operator definitions required by CHR do not
leak into modules where they might cause conflicts.
@node CHR Debugging, CHR Examples,CHR in YAP Programs, CHR
@section Debugging
@c \label{sec:debugging}
@c=================
The CHR debugging facilities are currently rather limited. Only tracing
is currently available. To use the CHR debugging facilities for a CHR
file it must be compiled for debugging. Generating debug info is
controlled by the CHR option @code{debug}, whose default is derived
from the SWI-Prolog flag @code{generate_debug_info}. Therefore debug
info is provided unless the @option{-nodebug} is used.
@subsection Ports
@c \label{sec:chrports
@c===============
For CHR constraints the four standard ports are defined:
@table @code
@item call
A new constraint is called and becomes active.
@item exit
An active constraint exits: it has either been inserted in the store after
trying all rules or has been removed from the constraint store.
@item fail
An active constraint fails.
@item redo
An active constraint starts looking for an alternative solution.
@end table
In addition to the above ports, CHR constraints have five additional
ports:
@table @code
@item wake
A suspended constraint is woken and becomes active.
@item insert
An active constraint has tried all rules and is suspended in
the constraint store.
@item remove
An active or passive constraint is removed from the constraint
store, if it had been inserted.
@item try
An active constraints tries a rule with possibly
some passive constraints. The try port is entered
just before committing to the rule.
@item apply
An active constraints commits to a rule with possibly
some passive constraints. The apply port is entered
just after committing to the rule.
@end table
@subsection Tracing
@c=================
Tracing is enabled with the chr_trace/0 predicate
and disabled with the chr_notrace/0 predicate.
When enabled the tracer will step through the @code{call},
@code{exit}, @code{fail}, @code{wake} and @code{apply} ports,
accepting debug commands, and simply write out the other ports.
The following debug commans are currently supported:
@example
CHR debug options:
<cr> creep c creep
s skip
g ancestors
n nodebug
b break
a abort
f fail
? help h help
@end example
Their meaning is:
@table @code
@item creep
Step to the next port.
@item skip
Skip to exit port of this call or wake port.
@item ancestors
Print list of ancestor call and wake ports.
@item nodebug
Disable the tracer.
@item break
Enter a recursive Prolog toplevel. See break/0.
@item abort
Exit to the toplevel. See abort/0.
@item fail
Insert failure in execution.
@item help
Print the above available debug options.
@end table
@subsection CHR Debugging Predicates
@c \label{sec:predicates
@c====================================
The @file{chr} module contains several predicates that allow
inspecting and printing the content of the constraint store.
@table @code
@item chr_trace/0
Activate the CHR tracer. By default the CHR tracer is activated and
deactivated automatically by the Prolog predicates trace/0 and
notrace/0.
@item chr_notrace/0
De-activate the CHR tracer. By default the CHR tracer is activated and
deactivated automatically by the Prolog predicates trace/0 and
notrace/0.
@item chr_leash/0
Define the set of CHR ports on which the CHR
tracer asks for user intervention (i.e. stops). @var{Spec} is either a
list of ports or a predefined `alias'. Defined aliases are:
@code{full} to stop at all ports, @code{none} or @code{off} to never
stop, and @code{default} to stop at the @code{call}, @code{exit},
@code{fail}, @code{wake} and @code{apply} ports. See also leash/1.
@item chr_show_store(+@var{Mod})
Prints all suspended constraints of module @var{Mod} to the standard
output. This predicate is automatically called by the SWI-Prolog toplevel at
the end of each query for every CHR module currently loaded. The prolog-flag
@code{chr_toplevel_show_store} controls whether the toplevel shows the
constraint stores. The value @code{true} enables it. Any other value
disables it.
@end table
@node CHR Examples, CHR Compatibility,CHR Debugging, CHR
@section Examples
@c \label{sec:examples}
@c================
Here are two example constraint solvers written in CHR.
@itemize
@item
The program below defines a solver with one constraint,
@code{leq/2}, which is a less-than-or-equal constraint.
@example
:- module(leq,[cycle/3, leq/2]).
:- use_module(library(chr)).
:- constraints leq/2.
reflexivity @ leq(X,X) <=> true.
antisymmetry @ leq(X,Y), leq(Y,X) <=> X = Y.
idempotence @ leq(X,Y) \ leq(X,Y) <=> true.
transitivity @ leq(X,Y), leq(Y,Z) ==> leq(X,Z).
cycle(X,Y,Z):-
leq(X,Y),
leq(Y,Z),
leq(Z,X).
@end example
@item
The program below implements a simple finite domain
constraint solver.
@example
:- module(dom,[dom/2]).
:- use_module(library(chr)).
:- constraints dom/2.
dom(X,[]) <=> fail.
dom(X,[Y]) <=> X = Y.
dom(X,L1), dom(X,L2) <=> intersection(L1,L2,L3), dom(X,L3).
intersection([],_,[]).
intersection([H|T],L2,[H|L3]) :-
member(H,L2), !,
intersection(T,L2,L3).
intersection([_|T],L2,L3) :-
intersection(T,L2,L3).
@end example
@end itemize
@node CHR Compatibility, CHR Guidelines,CHR Examples, CHR
@section Compatibility with SICStus CHR
@c \label{sec:sicstus-chr}
@c==================
There are small differences between CHR in SWI-Prolog and newer
YAPs and SICStus and older versions of YAP. Besides differences in
available options and pragmas, the following differences should be
noted:
@table @code
@item [The handler/1 declaration]
In SICStus every CHR module requires a @code{handler/1}
declaration declaring a unique handler name. This declaration is valid
syntax in SWI-Prolog, but will have no effect. A warning will be given
during compilation.
@item [The rules/1 declaration]
In SICStus, for every CHR module it is possible to only enable a subset
of the available rules through the @code{rules/1} declaration. The
declaration is valid syntax in SWI-Prolog, but has no effect. A
warning is given during compilation.
@item [Sourcefile naming]
SICStus uses a two-step compiler, where @file{chr} files are
first translated into @file{pl} files. For SWI-Prolog CHR
rules may be defined in a file with any extension.
@end table
@node CHR Guidelines, ,CHR Compatibility, CHR
@section Guidelines
@c \label{sec:guidelines}
@c ==================
In this section we cover several guidelines on how to use CHR to write
constraint solvers and how to do so efficiently.
@table @code
@item [Set semantics]
The CHR system allows the presence of identical constraints, i.e.
multiple constraints with the same functor, arity and arguments. For
most constraint solvers, this is not desirable: it affects efficiency
and possibly termination. Hence appropriate simpagation rules should be
added of the form:
@example
@{constraint \ constraint <=> true@}.
@end example
@item [Multi-headed rules]
Multi-headed rules are executed more efficiently when the constraints
share one or more variables.
@item [Mode and type declarations]
Provide mode and type declarations to get more efficient program execution.
Make sure to disable debug (@option{-nodebug}) and enable optimization
(@option{-O}).
@end table

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docs/clpr.tex Normal file
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@ -0,0 +1,180 @@
@chapter Constraint Logic Programming over Reals
YAP now uses the CLP(R) package developed by @emph{Leslie De Koninck},
K.U. Leuven as part of a thesis with supervisor Bart Demoen and daily
advisor Tom Schrijvers, and distributed with SWI-Prolog.
This CLP(R) system is a port of the CLP(Q,R) system of Sicstus Prolog
and YAP by Christian Holzbaur: Holzbaur C.: OFAI clp(q,r) Manual,
Edition 1.3.3, Austrian Research Institute for Artificial
Intelligence, Vienna, TR-95-09, 1995,
@url{http://www.ai.univie.ac.at/cgi-bin/tr-online?number+95-09} This
port only contains the part concerning real arithmetics. This manual
is roughly based on the manual of the above mentioned @strong{CLP(QR)}
implementation.
Please note that the @file{clpr} library is @emph{not} an
@code{autoload} library and therefore this library must be loaded
explicitely before using it:
@example
:- use_module(library(clpr)).
@end example
@node CLPR Solver Predicates, CLPR Syntax , , CLPR
@section Solver Predicates
@c =============================
The following predicates are provided to work with constraints:
@table @code
@item @{+@var{Constraints}@}
Adds the constraints given by @var{Constraints} to the constraint store.
@item entailed(+@var{Constraint})
Succeeds if @var{Constraint} is necessarily true within the current
constraint store. This means that adding the negation of the constraint
to the store results in failure.
@item inf(+@var{Expression},-@var{Inf})
Computes the infimum of @var{Expression} within the current state of the
constraint store and returns that infimum in @var{Inf}. This predicate
does not change the constraint store.
@item inf(+@var{Expression},-@var{Sup})
Computes the supremum of @var{Expression} within the current state of
the constraint store and returns that supremum in @var{Sup}. This
predicate does not change the constraint store.
@item min(+@var{Expression})
Minimizes @var{Expression} within the current constraint store. This is
the same as computing the infimum and equation the expression to that
infimum.
@item max(+@var{Expression})
Maximizes @var{Expression} within the current constraint store. This is
the same as computing the supremum and equating the expression to that
supremum.
@item bb_inf(+@var{Ints},+@var{Expression},-@var{Inf},-@var{Vertext},+@var{Eps})
Computes the infimum of @var{Expression} within the current constraint
store, with the additional constraint that in that infimum, all
variables in @var{Ints} have integral values. @var{Vertex} will contain
the values of @var{Ints} in the infimum. @var{Eps} denotes how much a
value may differ from an integer to be considered an integer. E.g. when
@var{Eps} = 0.001, then X = 4.999 will be considered as an integer (5 in
this case). @var{Eps} should be between 0 and 0.5.
@item bb_inf(+@var{Ints},+@var{Expression},-@var{Inf})
The same as bb_inf/5 but without returning the values of the integers
and with an eps of 0.001.
@item bb_inf(+@var{Target},+@var{Newvars},-@var{CodedAnswer})
Returns the constraints on @var{Target} in the list @var{CodedAnswer}
where all variables of @var{Target} have veen replaced by @var{NewVars}.
This operation does not change the constraint store. E.g. in
@example
dump([X,Y,Z],[x,y,z],Cons)
@end example
@var{Cons} will contain the constraints on @var{X}, @var{Y} and
@var{Z} where these variables have been replaced by atoms @code{x}, @code{y} and @code{z}.
@end table
@node CLPR Syntax, CLPR Unification, CLPR Solver Predicates, CLPR
@section Syntax of the predicate arguments
@c =============================================
The arguments of the predicates defined in the subsection above are
defined in the following table. Failing to meet the syntax rules will
result in an exception.
@example
<Constraints> ---> <Constraint> \\ single constraint \\
| <Constraint> , <Constraints> \\ conjunction \\
| <Constraint> ; <Constraints> \\ disjunction \\
<Constraint> ---> <Expression> @{<@} <Expression> \\ less than \\
| <Expression> @{>@} <Expression> \\ greater than \\
| <Expression> @{=<@} <Expression> \\ less or equal \\
| @{<=@}(<Expression>, <Expression>) \\ less or equal \\
| <Expression> @{>=@} <Expression> \\ greater or equal \\
| <Expression> @{=\=@} <Expression> \\ not equal \\
| <Expression> =:= <Expression> \\ equal \\
| <Expression> = <Expression> \\ equal \\
<Expression> ---> <Variable> \\ Prolog variable \\
| <Number> \\ Prolog number (float, integer) \\
| +<Expression> \\ unary plus \\
| -<Expression> \\ unary minus \\
| <Expression> + <Expression> \\ addition \\
| <Expression> - <Expression> \\ substraction \\
| <Expression> * <Expression> \\ multiplication \\
| <Expression> / <Expression> \\ division \\
| abs(<Expression>) \\ absolute value \\
| sin(<Expression>) \\ sine \\
| cos(<Expression>) \\ cosine \\
| tan(<Expression>) \\ tangent \\
| exp(<Expression>) \\ exponent \\
| pow(<Expression>) \\ exponent \\
| <Expression> @{^@} <Expression> \\ exponent \\
| min(<Expression>, <Expression>) \\ minimum \\
| max(<Expression>, <Expression>) \\ maximum \\
@end example
@node CLPR Unification, CLPR Non-linear Constraints, CLPR Syntax, CLPR
@section Use of unification
Instead of using the @code{@{@}/1} predicate, you can also use the standard
unification mechanism to store constraints. The following code samples
are equivalent:
@table @option
@item Unification with a variable
@example
@{X =:= Y@}
@{X = Y@}
X = Y
@end example
@item Unification with a number
@example
@{X =:= 5.0@}
@{X = 5.0@}
X = 5.0
@end example
@end table
@node CLPR Non-linear Constraints, , CLPR Unification, CLPR
@section Non-Linear Constraints
@c ==================================
In this version, non-linear constraints do not get solved until certain
conditions are satisfied. We call these conditions the isolation axioms.
They are given in the following table.
@example
A = B * C when B or C is ground or // A = 5 * C or A = B * 4 \\
A and (B or C) are ground // 20 = 5 * C or 20 = B * 4 \\
A = B / C when C is ground or // A = B / 3
A and B are ground // 4 = 12 / C
X = min(Y,Z) when Y and Z are ground or // X = min(4,3)
X = max(Y,Z) Y and Z are ground // X = max(4,3)
X = abs(Y) Y is ground // X = abs(-7)
X = pow(Y,Z) when X and Y are ground or // 8 = 2 ^ Z
X = exp(Y,Z) X and Z are ground // 8 = Y ^ 3
X = Y ^ Z Y and Z are ground // X = 2 ^ 3
X = sin(Y) when X is ground or // 1 = sin(Y)
X = cos(Y) Y is ground // X = sin(1.5707)
X = tan(Y)
@end example

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@chapter SWI-Prolog Emulation
This library provides a number of SWI-Prolog builtins that are not by
default in YAP. This library is loaded with the
@code{use_module(library(swi))} command.
@table @code
@item append(?@var{List1},?@var{List2},?@var{List3})
@findex append/3
@snindex append/3
@cnindex append/3
Succeeds when @var{List3} unifies with the concatenation of @var{List1}
and @var{List2}. The predicate can be used with any instantiation
pattern (even three variables).
@item between(+@var{Low},+@var{High},?@var{Value})
@findex between/3
@snindex between/3
@cnindex between/3
@var{Low} and @var{High} are integers, @var{High} less or equal than
@var{Low}. If @var{Value} is an integer, @var{Low} less or equal than
@var{Value} less or equal than @var{High}. When @var{Value} is a
variable it is successively bound to all integers between @var{Low} and
@var{High}. If @var{High} is @code{inf}, @code{between/3} is true iff
@var{Value} less or equal than @var{Low}, a feature that is particularly
interesting for generating integers from a certain value.
@item chdir(+@var{Dir})
@findex chdir/1
@snindex chdir/1
@cnindex chdir/1
Compatibility predicate. New code should use @code{working_directory/2}.
@item concat_atom(+@var{List},-@var{Atom})
@findex concat_atom/2
@snindex concat_atom/2
@cnindex concat_atom/2
@var{List} is a list of atoms, integers or floating point numbers. Succeeds
if @var{Atom} can be unified with the concatenated elements of @var{List}. If
@var{List} has exactly 2 elements it is equivalent to @code{atom_concat/3},
allowing for variables in the list.
@item concat_atom(?@var{List},+@var{Separator},?@var{Atom})
@findex concat_atom/3
@snindex concat_atom/3
@cnindex concat_atom/3
Creates an atom just like concat_atom/2, but inserts @var{Separator}
between each pair of atoms. For example:
\@example
?- concat_atom([gnu, gnat], ', ', A).
A = 'gnu, gnat'
@end example
(Unimplemented) This predicate can also be used to split atoms by
instantiating @var{Separator} and @var{Atom}:
@example
?- concat_atom(L, -, 'gnu-gnat').
L = [gnu, gnat]
@end example
@item nth1(+@var{Index},?@var{List},?@var{Elem})
@findex nth1/3
@snindex nth1/3
@cnindex nth1/3
Succeeds when the @var{Index}-th element of @var{List} unifies with
@var{Elem}. Counting starts at 1.
Set environment variable. @var{Name} and @var{Value} should be
instantiated to atoms or integers. The environment variable will be
passed to @code{shell/[0-2]} and can be requested using @code{getenv/2}.
They also influence @code{expand_file_name/2}.
@item setenv(+@var{Name},+@var{Value})
@findex setenv/2
@snindex setenv/2
@cnindex setenv/2
Set environment variable. @var{Name} and @var{Value} should be
instantiated to atoms or integers. The environment variable will be
passed to @code{shell/[0-2]} and can be requested using @code{getenv/2}.
They also influence @code{expand_file_name/2}.
@item term_to_atom(?@var{Term},?@var{Atom})
@findex term_to_atom/2
@snindex term_to_atom/2
@cnindex term_to_atom/2
Succeeds if @var{Atom} describes a term that unifies with @var{Term}. When
@var{Atom} is instantiated @var{Atom} is converted and then unified with
@var{Term}. If @var{Atom} has no valid syntax, a @code{syntax_error}
exception is raised. Otherwise @var{Term} is ``written'' on @var{Atom}
using @code{write/1}.
@item working_directory(-@var{Old},+@var{New})
@findex working_directory/2
@snindex working_directory/2
@cnindex working_directory/2
Unify @var{Old} with an absolute path to the current working directory
and change working directory to @var{New}. Use the pattern
@code{working_directory(CWD, CWD)} to get the current directory. See
also @code{absolute_file_name/2} and @code{chdir/1}.
@end table
@node Invoking Predicates on all Members of a List,Forall, , SWI-Prolog
@section Invoking Predicates on all Members of a List
@c \label{sec:applylist}
All the predicates in this section call a predicate on all members of a
list or until the predicate called fails. The predicate is called via
@code{call/[2..]}, which implies common arguments can be put in
front of the arguments obtained from the list(s). For example:
@example
?- maplist(plus(1), [0, 1, 2], X).
X = [1, 2, 3]
@end example
we will phrase this as ``@var{Predicate} is applied on ...''
@table @code
@item maplist(+@var{Pred},+@var{List})
@findex maplist/2
@snindex maplist/2
@cnindex maplist/2
@var{Pred} is applied successively on each element of @var{List} until
the end of the list or @var{Pred} fails. In the latter case
@code{maplist/2} fails.
@item maplist(+@var{Pred},+@var{List1},+@var{List2})
@findex maplist/3
@snindex maplist/3
@cnindex maplist/3
Apply @var{Pred} on all successive triples of elements from
@var{List1} and
@var{List2}. Fails if @var{Pred} can not be applied to a
pair. See the example above.
@item maplist(+@var{Pred},+@var{List1},+@var{List2},+@var{List4})
@findex maplist/4
@snindex maplist/4
@cnindex maplist/4
Apply @var{Pred} on all successive triples of elements from @var{List1},
@var{List2} and @var{List3}. Fails if @var{Pred} can not be applied to a
triple. See the example above.
@c @item findlist(+@var{Pred},+@var{List1},?@var{List2})
@c @findex findlist/3
@c @snindex findlist/3
@c @cnindex findlist/3
@c Unify @var{List2} with a list of all elements of @var{List1} to which
@c @var{Pred} applies.
@end table
@node Forall,hProlog and SWI-Prolog Attributed Variables,Invoking Predicates on all Members of a List, SWI-Prolog
@section Forall
@c \label{sec:forall2}
@table @code
@item forall(+@var{Cond},+@var{Action})
@findex forall/2
@snindex forall/2
@cnindex forall/2
For all alternative bindings of @var{Cond} @var{Action} can be proven.
The next example verifies that all arithmetic statements in the list
@var{L} are correct. It does not say which is wrong if one proves wrong.
@example
?- forall(member(Result = Formula, [2 = 1 + 1, 4 = 2 * 2]),
Result =:= Formula).
@end example
@end table
@node hProlog and SWI-Prolog Attributed Variables, SWI-Prolog Global Variables, Forall,SWI-Prolog
@section hProlog and SWI-Prolog Attributed Variables
@cindex hProlog Attributed Variables
Attributed variables
@c @ref{Attributed variables}
provide a technique for extending the
Prolog unification algorithm by hooking the binding of attributed
variables. There is little consensus in the Prolog community on the
exact definition and interface to attributed variables. Yap Prolog
traditionally implements a SICStus-like interface, but to enable
SWI-compatibility we have implemented the SWI-Prolog interface,
identical to the one realised by Bart Demoen for hProlog.
Binding an attributed variable schedules a goal to be executed at the
first possible opportunity. In the current implementation the hooks are
executed immediately after a successful unification of the clause-head
or successful completion of a foreign language (builtin) predicate. Each
attribute is associated to a module and the hook (attr_unify_hook/2) is
executed in this module. The example below realises a very simple and
incomplete finite domain reasoner.
@example
:- module(domain,
[ domain/2 % Var, ?Domain
]).
:- use_module(library(oset)).
domain(X, Dom) :-
var(Dom), !,
get_attr(X, domain, Dom).
domain(X, List) :-
sort(List, Domain),
put_attr(Y, domain, Domain),
X = Y.
% An attributed variable with attribute value Domain has been
% assigned the value Y
attr_unify_hook(Domain, Y) :-
( get_attr(Y, domain, Dom2)
-> oset_int(Domain, Dom2, NewDomain),
( NewDomain == []
-> fail
; NewDomain = [Value]
-> Y = Value
; put_attr(Y, domain, NewDomain)
)
; var(Y)
-> put_attr( Y, domain, Domain )
; memberchk(Y, Domain)
).
@end example
Before explaining the code we give some example queries:
@table @code
@item ?- domain(X, [a,b]), X = c
no
@item ?- domain(X, [a,b]), domain(X, [a,c]).
X = a
@item ?- domain(X, [a,b,c]), domain(X, [a,c]).
X = _D0
@end table
The predicate @code{domain/2} fetches (first clause) or assigns
(second clause) the variable a @emph{domain}, a set of values it can
be unified with. In the second clause first associates the domain
with a fresh variable and then unifies X to this variable to deal
with the possibility that X already has a domain. The
predicate @code{attr_unify_hook/2} is a hook called after a variable with
a domain is assigned a value. In the simple case where the variable
is bound to a concrete value we simply check whether this value is in
the domain. Otherwise we take the intersection of the domains and either
fail if the intersection is empty (first example), simply assign the
value if there is only one value in the intersection (second example) or
assign the intersection as the new domain of the variable (third
example).
@table @code
@item put_attr(+@var{Var},+@var{Module},+@var{Value})
@findex put_attr/3
@snindex put_attr/3
@cnindex put_attr/3
If @var{Var} is a variable or attributed variable, set the value for the
attribute named @var{Module} to @var{Value}. If an attribute with this
name is already associated with @var{Var}, the old value is replaced.
Backtracking will restore the old value (i.e. an attribute is a mutable
term. See also @code{setarg/3}). This predicate raises a type error if
@var{Var} is not a variable or @var{Module} is not an atom.
@item get_attr(+@var{Var},+@var{Module},+@var{Value})
@findex get_attr/3
@snindex get_attr/3
@cnindex get_attr/3
Request the current @var{value} for the attribute named @var{Module}. If
@var{Var} is not an attributed variable or the named attribute is not
associated to @var{Var} this predicate fails silently. If @var{Module}
is not an atom, a type error is raised.
@item del_attr(+@var{Var},+@var{Module})
@findex del_attr/2
@snindex del_attr/2
@cnindex del_attr/2
Delete the named attribute. If @var{Var} loses its last attribute it
is transformed back into a traditional Prolog variable. If @var{Module}
is not an atom, a type error is raised. In all other cases this
predicate succeeds regarless whether or not the named attribute is
present.
@item attr_unify_hook(+@var{AttValue},+@var{VarValue})
@findex attr_unify_hook/2
@snindex attr_unify_hook/2
@cnindex attr_unify_hook/2
Hook that must be defined in the module an attributed variable refers
to. Is is called @emph{after} the attributed variable has been
unified with a non-var term, possibly another attributed variable.
@var{AttValue} is the attribute that was associated to the variable
in this module and @var{VarValue} is the new value of the variable.
Normally this predicate fails to veto binding the variable to
@var{VarValue}, forcing backtracking to undo the binding. If
@var{VarValue} is another attributed variable the hook often combines
the two attribute and associates the combined attribute with
@var{VarValue} using @code{put_attr/3}.
@c \predicate{attr_portray_hook}{2}{+AttValue, +Var}
@c Called by write_term/2 and friends for each attribute if the option
@c \term{attributes}{portray} is in effect. If the hook succeeds the
@c attribute is considered printed. Otherwise \exam{Module = ...} is
@c printed to indicate the existence of a variable.
@end table
@subsection Special Purpose SWI Predicates for Attributes
Normal user code should deal with @code{put_attr/3}, @code{get_attr/3}
and @code{del_attr/2}. The routines in this section fetch or set the
entire attribute list of a variables. Use of these predicates is
anticipated to be restricted to printing and other special purpose
operations.
@table @code
@item get_attrs(+@var{Var},-@var{Attributes})
@findex get_attrs/2
@snindex get_attrs/2
@cnindex get_attrs/2
Get all attributes of @var{Var}. @var{Attributes} is a term of the form
@code{att(Module, Value, MoreAttributes)}, where @var{MoreAttributes} is
@code{[]} for the last attribute.
@item put_attrs(+@var{Var},+@var{Attributes})
@findex put_attrs/2
@snindex put_attrs/2
@cnindex put_attrs/2
Set all attributes of @var{Var}. See get_attrs/2 for a description of
@var{Attributes}.
@item copy_term_nat(?@var{TI},-@var{TF})
@findex copy_term_nat/2
@snindex copy_term_nat/2
@cnindex copy_term_nat/2
As @code{copy_term/2}. Attributes however, are @emph{not} copied but replaced
by fresh variables.
@end table
@node SWI-Prolog Global Variables, ,hProlog and SWI-Prolog Attributed Variables,SWI-Prolog
@section SWI Global variables
@c \label{sec:gvar}
SWI-Prolog global variables are associations between names (atoms) and
terms. They differ in various ways from storing information using
@code{assert/1} or @code{recorda/3}.
@itemize @bullet
@item The value lives on the Prolog (global) stack. This implies
that lookup time is independent from the size of the term.
This is particulary interesting for large data structures
such as parsed XML documents or the CHR global constraint
store.
@item They support both global assignment using @code{nb_setval/2} and
backtrackable assignment using @code{b_setval/2}.
@item Only one value (which can be an arbitrary complex Prolog
term) can be associated to a variable at a time.
@item Their value cannot be shared among threads. Each thread
has its own namespace and values for global variables.
@item Currently global variables are scoped globally. We may
consider module scoping in future versions.
@end itemize
Both @code{b_setval/2} and @code{nb_setval/2} implicitely create a variable if the
referenced name does not already refer to a variable.
Global variables may be initialised from directives to make them
available during the program lifetime, but some considerations are
necessary for saved-states and threads. Saved-states to not store global
variables, which implies they have to be declared with @code{initialization/1}
to recreate them after loading the saved state. Each thread has
its own set of global variables, starting with an empty set. Using
@code{thread_inititialization/1} to define a global variable it will be
defined, restored after reloading a saved state and created in all
threads that are created @emph{after} the registration.
@table @code
@item b_setval(+@var{Name},+@var{Value})
@findex b_setval/2
@snindex b_setval/2
@cnindex b_setval/2
Associate the term @var{Value} with the atom @var{Name} or replaces
the currently associated value with @var{Value}. If @var{Name} does
not refer to an existing global variable a variable with initial value
@code{[]} is created (the empty list). On backtracking the
assignment is reversed.
@item b_getval(+@var{Name},-@var{Value})
@findex b_getval/2
@snindex b_getval/2
@cnindex b_getval/2
Get the value associated with the global variable @var{Name} and unify
it with @var{Value}. Note that this unification may further instantiate
the value of the global variable. If this is undesirable the normal
precautions (double negation or @code{copy_term/2}) must be taken. The
@code{b_getval/2} predicate generates errors if @var{Name} is not an atom or
the requested variable does not exist.
@end table
@table @code
@item nb_setval(+@var{Name},+@var{Value})
@findex nb_setval/2
@snindex nb_setval/2
@cnindex nb_setval/2
Associates a copy of @var{Value} created with @code{duplicate_term/2}
with the atom @var{Name}. Note that this can be used to set an
initial value other than @code{[]} prior to backtrackable assignment.
@item nb_getval(+@var{Name},-@var{Value})
@findex nb_getval/2
@snindex nb_getval/2
@cnindex nb_getval/2
The @code{nb_getval/2} predicate is a synonym for b_getval/2, introduced for
compatibility and symetry. As most scenarios will use a particular
global variable either using non-backtracable or backtrackable
assignment, using @code{nb_getval/2} can be used to document that the
variable is used non-backtracable.
@c \predicate{nb_linkval}{2}{+Name, +Value}
@c Associates the term @var{Value} with the atom @var{Name} without copying
@c it. This is a fast special-purpose variation of nb_setval/2 intended for
@c expert users only because the semantics on backtracking to a point
@c before creating the link are poorly defined for compound terms. The
@c principal term is always left untouched, but backtracking behaviour on
@c arguments is undone if the orginal assignment was \jargon{trailed} and
@c left alone otherwise, which implies that the history that created the
@c term affects the behaviour on backtracking. Please consider the
@c following example:
@c \begin{code}
@c demo_nb_linkval :-
@c T = nice(N),
@c ( N = world,
@c nb_linkval(myvar, T),
@c fail
@c ; nb_getval(myvar, V),
@c writeln(V)
@c ).
@c \end{code}
@item nb_current(?@var{Name},?@var{Value})
@findex nb_current/2
@snindex nb_current/2
@cnindex nb_current/2
Enumerate all defined variables with their value. The order of
enumeration is undefined.
@item nb_delete(?@var{Name})
@findex nb_delete/1
@snindex nb_delete/1
@cnindex nb_delete/1
Delete the named global variable.
@end table
@subsection Compatibility of SWI-Prolog Global Variables
Global variables have been introduced by various Prolog
implementations recently. The implementation of them in SWI-Prolog is
based on hProlog by Bart Demoen. In discussion with Bart it was
decided that the semantics if hProlog @code{nb_setval/2}, which is
equivalent to @code{nb_linkval/2} is not acceptable for normal Prolog
users as the behaviour is influenced by how builtin predicates
constructing terms (@code{read/1}, @code{=../2}, etc.) are implemented.
GNU-Prolog provides a rich set of global variables, including arrays.
Arrays can be implemented easily in SWI-Prolog using @code{functor/3} and
@code{setarg/3} due to the unrestricted arity of compound terms.
@node Extensions,Debugging,SWI-Prolog,Top
@chapter Extensions to Prolog
YAP includes several extensions that are not enabled by
default, but that can be used to extend the functionality of the
system. These options can be set at compilation time by enabling the
related compilation flag, as explained in the @code{Makefile}

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