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12
C/flags.c
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@ -18,8 +18,16 @@
/** @file C/flags.c
@{
@addtogroup Flags
@ingroup builtins
@defgroup YAPFlags_Impl C-code to handle Prolog flags.
@ingroup YAPFlags
@brief Low-level code to support flags. Flags can be:
= thread-local or global
= module-based or module-independent.
= read-only or read-write
= System or User Defined.
= Have type boolean, number, atom constant or may be a general term.
*/
// this is where we define flags

10
H/YapGFlagInfo.h
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@ -72,17 +72,17 @@ YAP_FLAG(ANSWER_FORMAT_FLAG, "answer_format", true, isatom, "~p",
Read-write flag telling whether arithmetic exceptions generate
Prolog exceptions. If enabled:
~~~~
~~~
?- X is 2/0.
ERROR!!
ZERO DIVISO]]R ERROR- X is Exp
~~~~
ZERO DIVISOR ERROR- X is Exp
~~~
If disabled:
~~~~
~~~
?- X is 2/0.
X = (+inf).
~~~~
~~~
It is `true` by default, but it is disabled by packages like CLP(BN) and
ProbLog.

2
H/YapLFlagInfo.h
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@ -131,3 +131,5 @@ YAP_FLAG( USER_INPUT_FLAG, "user_input", true, stream, "user_input" , set_input
} local_flag_t;
/// @}

2
docs/Doxyfile.in
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@ -1179,7 +1179,7 @@ HTML_FOOTER =
# obsolete.
# This tag requires that the tag GENERATE_HTML is set to YES.
HTML_STYLESHEET = YES
HTML_STYLESHEET =
# The HTML_EXTRA_STYLESHEET tag can be used to specify additional user-defined
# cascading style sheets that are included after the standard style sheets

4
docs/md/INSTALL.md
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@ -1,9 +1,9 @@
Installing YAP {#INSTALL}
++++++++
### Downloading YAP {#download}
### Downloading YAP {#Download}
The latest development version of Yap-6 is available source-only
through GIT repositories. The main reference repository is at

360
docs/md/attributes.md
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@ -24,13 +24,371 @@ From YAP-6.0.3 onwards we recommend using the hProlog, SWI style
interface. We believe that this design is easier to understand and
work with. Most packages included in YAP that use attributed
variables, such as CHR, CLP(FD), and CLP(QR), rely on the SWI-Prolog
interface.
awi interface.
+ @ref SICS_attributes
+ @ref sicsatts
+ @ref New_Style_Attribute_Declarations
+ @ref CohYroutining
+ @ref AttributeVariables_Builtins
### SICStus Style attribute declarations. {#SICS_attributes}
The YAP library `atts` implements attribute variables in the style of
SICStus Prolog. Attributed variables work as follows:
+ Each attribute must be declared beforehand. Attributes are described
as a functor with name and arity and are local to a module. Each
Prolog module declares its own sets of attributes. Different modules
may have attributes with the same name and arity.
+ The built-in put_atts/2 adds or deletes attributes to a
variable. The variable may be unbound or may be an attributed
variable. In the latter case, YAP discards previous values for the
attributes.
+ The built-in get_atts/2 can be used to check the values of
an attribute associated with a variable.
+ The unification algorithm calls the user-defined predicate
verify_attributes/3 before trying to bind an attributed
variable. Unification will resume after this call.
+ The user-defined predicate
<tt>attribute_goal/2</tt> converts from an attribute to a goal.
+ The user-defined predicate
<tt>project_attributes/2</tt> is used from a set of variables into a set of
constraints or goals. One application of <tt>project_attributes/2</tt> is in
the top-level, where it is used to output the set of
floundered constraints at the end of a query.
Attributes are compound terms associated with a variable. Each attribute
has a <em>name</em> which is <em>private</em> to the module in which the
attribute was defined. Variables may have at most one attribute with a
name. Attribute names are defined through the following declaration:
~~~~~
:- attribute AttributeSpec, ..., AttributeSpec.
~~~~~
where each _AttributeSpec_ has the form ( _Name_/ _Arity_).
One single such declaration is allowed per module _Module_.
Although the YAP module system is predicate based, attributes are local
to modules. This is implemented by rewriting all calls to the
built-ins that manipulate attributes so that attribute names are
preprocessed depending on the module. The `user:goal_expansion/3`
mechanism is used for this purpose.
The attribute manipulation predicates always work as follows:
+ The first argument is the unbound variable associated with
attributes,
+ 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.
The following three procedures are available to the user. Notice that
these built-ins are rewritten by the system into internal built-ins, and
that the rewriting process <em>depends</em> on the module on which the
built-ins have been invoked.
The user-predicate predicate verify_attributes/3 is called when
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:
Constraint solvers must be able to project a set of constraints to a set
of variables. This is useful when displaying the solution to a goal, but
may also be used to manipulate computations. The user-defined
project_attributes/2 is responsible for implementing this
projection.
The following examples are taken from the SICStus Prolog
manual. The sketches the implementation of a simple finite domain
`solver`. Note that an industrial strength solver would have to
provide a wider range of functionality and that it quite likely would
utilize a more efficient representation for the domains proper. The
module exports a single predicate `domain( _-Var_, _?Domain_)` which
associates _Domain_ (a list of terms) with _Var_. A variable can be
queried for its domain by leaving _Domain_ unbound.
We do not present here a definition for project_attributes/2.
Projecting finite domain constraints happens to be difficult.
~~~~~
:- module(domain, [domain/2]).
:- use_module(library(atts)).
:- use_module(library(ordsets), [
ord_intersection/3,
ord_intersect/2,
list_to_ord_set/2
]).
:- attribute dom/1.
verify_attributes(Var, Other, Goals) :-
get_atts(Var, dom(Da)), !, % are we involved?
( var(Other) -> % must be attributed then
( get_atts(Other, dom(Db)) -> % has a domain?
ord_intersection(Da, Db, Dc),
Dc = [El|Els], % at least one element
( Els = [] -> % exactly one element
Goals = [Other=El] % implied binding
; Goals = [],
put_atts(Other, dom(Dc))% rescue intersection
)
; Goals = [],
put_atts(Other, dom(Da)) % rescue the domain
)
; Goals = [],
ord_intersect([Other], Da) % value in domain?
).
verify_attributes(_, _, []). % unification triggered
% because of attributes
% in other modules
attribute_goal(Var, domain(Var,Dom)) :- % interpretation as goal
get_atts(Var, dom(Dom)).
domain(X, Dom) :-
var(Dom), !,
get_atts(X, dom(Dom)).
domain(X, List) :-
list_to_ord_set(List, Set),
Set = [El|Els], % at least one element
( Els = [] -> % exactly one element
X = El % implied binding
; put_atts(Fresh, dom(Set)),
X = Fresh % may call
% verify_attributes/3
).
~~~~~
Note that the _implied binding_ `Other=El` was deferred until after
the completion of `verify_attribute/3`. Otherwise, there might be a
danger of recursively invoking `verify_attribute/3`, which might bind
`Var`, which is not allowed inside the scope of `verify_attribute/3`.
Deferring unifications into the third argument of `verify_attribute/3`
effectively serializes the calls to `verify_attribute/3`.
Assuming that the code resides in the file domain.yap, we
can use it via:
~~~~~
| ?- use_module(domain).
~~~~~
Let's test it:
~~~~~
| ?- domain(X,[5,6,7,1]), domain(Y,[3,4,5,6]), domain(Z,[1,6,7,8]).
domain(X,[1,5,6,7]),
domain(Y,[3,4,5,6]),
domain(Z,[1,6,7,8]) ?
yes
| ?- domain(X,[5,6,7,1]), domain(Y,[3,4,5,6]), domain(Z,[1,6,7,8]),
X=Y.
Y = X,
domain(X,[5,6]),
domain(Z,[1,6,7,8]) ?
yes
| ?- domain(X,[5,6,7,1]), domain(Y,[3,4,5,6]), domain(Z,[1,6,7,8]),
X=Y, Y=Z.
X = 6,
Y = 6,
Z = 6
~~~~~
To demonstrate the use of the _Goals_ argument of
verify_attributes/3, we give an implementation of
freeze/2. We have to name it `myfreeze/2` in order to
avoid a name clash with the built-in predicate of the same name.
~~~~~
:- module(myfreeze, [myfreeze/2]).
:- use_module(library(atts)).
:- attribute frozen/1.
verify_attributes(Var, Other, Goals) :-
get_atts(Var, frozen(Fa)), !, % are we involved?
( var(Other) -> % must be attributed then
( get_atts(Other, frozen(Fb)) % has a pending goal?
-> put_atts(Other, frozen((Fa,Fb))) % rescue conjunction
; put_atts(Other, frozen(Fa)) % rescue the pending goal
),
Goals = []
; Goals = [Fa]
).
verify_attributes(_, _, []).
attribute_goal(Var, Goal) :- % interpretation as goal
get_atts(Var, frozen(Goal)).
myfreeze(X, Goal) :- put_atts(Fresh, frozen(Goal)), Fresh = X. ~~~~~
Assuming that this code lives in file myfreeze.yap,
we would use it via:
~~~~~
| ?- use_module(myfreeze).
| ?- myfreeze(X,print(bound(x,X))), X=2.
bound(x,2) % side effect
X = 2 % bindings
~~~~~
The two solvers even work together:
~~~~~
| ?- myfreeze(X,print(bound(x,X))), domain(X,[1,2,3]),
domain(Y,[2,10]), X=Y.
bound(x,2) % side effect
X = 2, % bindings
Y = 2
~~~~~
The two example solvers interact via bindings to shared attributed
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`.
@}
@{
### hProlog and SWI-Prolog style Attribute Declarations {#New_Style_Attribute_Declarations}
The following documentation is taken from the SWI-Prolog manual.
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 (built-in) 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.
~~~~~
:- 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),
v 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)
-> ord_intersection(Domain, Dom2, NewDomain),
( NewDomain == []
-> fail
; NewDomain = [Value]
-> Y = Value
; put_attr(Y, domain, NewDomain)
)
; var(Y)
-> put_attr( Y, domain, Domain )
; ord_memberchk(Y, Domain)
).
% Translate attributes from this module to residual goals %
attribute_goals(X) -->
{ get_attr(X, domain, List) },
[domain(X, List)].
~~~~~
Before explaining the code 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
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 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). The nonterminal `attribute_goals/3` is used to translate
remaining attributes to user-readable goals that, when executed, reinstate
these attributes.
@}
@{
### 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
sufficiently instantiated. This may result in a more "data-driven"
execution, or may be necessary to correctly implement extensions such
as negation by failure.
Initially, YAP used a separate mechanism for co-routining. Nowadays, YAP uses
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.
+ 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
- dif/2
- when/2
- frozen/2
@}
@}

390
docs/md/atts.md
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@ -1,390 +0,0 @@
@ingroup extensions
YAP supports attributed variables, originally developed at OFAI by
Christian Holzbaur. Attributes are a means of declaring that an
arbitrary term is a property for a variable. These properties can be
updated during forward execution. Moreover, the unification algorithm is
aware of attributed variables and will call user defined handlers when
trying to unify these variables.
Attributed variables provide an elegant abstraction over which one can
extend Prolog systems. Their main application so far has been in
implementing constraint handlers, such as Holzbaur's CLPQR, Fruewirth
and Holzbaur's CHR, and CLP(BN).
Different Prolog systems implement attributed variables in different
ways. Originally, YAP used the interface designed by SICStus
Prolog. This interface is still
available through the <tt>atts</tt> library, and is used by CLPBN.
From YAP-6.0.3 onwards we recommend using the hProlog, SWI style
interface. We believe that this design is easier to understand and
work with. Most packages included in YAP that use attributed
variables, such as CHR, CLP(FD), and CLP(QR), rely on the SWI-Prolog
interface.
+ @ref SICS_attributes
+ @ref sicsatts
+ @ref New_Style_Attribute_Declarations
+ @ref AttributedVariables_Builtins
+ @ref attscorouts
### SICStus Style attribute declarations. {#SICS_attributes}
The YAP library `atts` implements attribute variables in the style of
SICStus Prolog. Attributed variables work as follows:
+ Each attribute must be declared beforehand. Attributes are described
as a functor with name and arity and are local to a module. Each
Prolog module declares its own sets of attributes. Different modules
may have attributes with the same name and arity.
+ The built-in put_atts/2 adds or deletes attributes to a
variable. The variable may be unbound or may be an attributed
variable. In the latter case, YAP discards previous values for the
attributes.
+ The built-in get_atts/2 can be used to check the values of
an attribute associated with a variable.
+ The unification algorithm calls the user-defined predicate
verify_attributes/3 before trying to bind an attributed
variable. Unification will resume after this call.
+ The user-defined predicate
<tt>attribute_goal/2</tt> converts from an attribute to a goal.
+ The user-defined predicate
<tt>project_attributes/2</tt> is used from a set of variables into a set of
constraints or goals. One application of <tt>project_attributes/2</tt> is in
the top-level, where it is used to output the set of
floundered constraints at the end of a query.
Attributes are compound terms associated with a variable. Each attribute
has a <em>name</em> which is <em>private</em> to the module in which the
attribute was defined. Variables may have at most one attribute with a
name. Attribute names are defined through the following declaration:
~~~~~
:- attribute AttributeSpec, ..., AttributeSpec.
~~~~~
where each _AttributeSpec_ has the form ( _Name_/ _Arity_).
One single such declaration is allowed per module _Module_.
Although the YAP module system is predicate based, attributes are local
to modules. This is implemented by rewriting all calls to the
built-ins that manipulate attributes so that attribute names are
preprocessed depending on the module. The `user:goal_expansion/3`
mechanism is used for this purpose.
The attribute manipulation predicates always work as follows:
+ The first argument is the unbound variable associated with
attributes,
+ 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.
The following three procedures are available to the user. Notice that
these built-ins are rewritten by the system into internal built-ins, and
that the rewriting process <em>depends</em> on the module on which the
built-ins have been invoked.
The user-predicate predicate verify_attributes/3 is called when
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:
Constraint solvers must be able to project a set of constraints to a set
of variables. This is useful when displaying the solution to a goal, but
may also be used to manipulate computations. The user-defined
project_attributes/2 is responsible for implementing this
projection.
The following examples are taken from the SICStus Prolog
manual. The sketches the implementation of a simple finite domain
`solver`. Note that an industrial strength solver would have to
provide a wider range of functionality and that it quite likely would
utilize a more efficient representation for the domains proper. The
module exports a single predicate `domain( _-Var_, _?Domain_)` which
associates _Domain_ (a list of terms) with _Var_. A variable can be
queried for its domain by leaving _Domain_ unbound.
We do not present here a definition for project_attributes/2.
Projecting finite domain constraints happens to be difficult.
~~~~~
:- module(domain, [domain/2]).
:- use_module(library(atts)).
:- use_module(library(ordsets), [
ord_intersection/3,
ord_intersect/2,
list_to_ord_set/2
]).
:- attribute dom/1.
verify_attributes(Var, Other, Goals) :-
get_atts(Var, dom(Da)), !, % are we involved?
( var(Other) -> % must be attributed then
( get_atts(Other, dom(Db)) -> % has a domain?
ord_intersection(Da, Db, Dc),
Dc = [El|Els], % at least one element
( Els = [] -> % exactly one element
Goals = [Other=El] % implied binding
; Goals = [],
put_atts(Other, dom(Dc))% rescue intersection
)
; Goals = [],
put_atts(Other, dom(Da)) % rescue the domain
)
; Goals = [],
ord_intersect([Other], Da) % value in domain?
).
verify_attributes(_, _, []). % unification triggered
% because of attributes
% in other modules
attribute_goal(Var, domain(Var,Dom)) :- % interpretation as goal
get_atts(Var, dom(Dom)).
domain(X, Dom) :-
var(Dom), !,
get_atts(X, dom(Dom)).
domain(X, List) :-
list_to_ord_set(List, Set),
Set = [El|Els], % at least one element
( Els = [] -> % exactly one element
X = El % implied binding
; put_atts(Fresh, dom(Set)),
X = Fresh % may call
% verify_attributes/3
).
~~~~~
Note that the _implied binding_ `Other=El` was deferred until after
the completion of `verify_attribute/3`. Otherwise, there might be a
danger of recursively invoking `verify_attribute/3`, which might bind
`Var`, which is not allowed inside the scope of `verify_attribute/3`.
Deferring unifications into the third argument of `verify_attribute/3`
effectively serializes the calls to `verify_attribute/3`.
Assuming that the code resides in the file domain.yap, we
can use it via:
~~~~~
| ?- use_module(domain).
~~~~~
Let's test it:
~~~~~
| ?- domain(X,[5,6,7,1]), domain(Y,[3,4,5,6]), domain(Z,[1,6,7,8]).
domain(X,[1,5,6,7]),
domain(Y,[3,4,5,6]),
domain(Z,[1,6,7,8]) ?
yes
| ?- domain(X,[5,6,7,1]), domain(Y,[3,4,5,6]), domain(Z,[1,6,7,8]),
X=Y.
Y = X,
domain(X,[5,6]),
domain(Z,[1,6,7,8]) ?
yes
| ?- domain(X,[5,6,7,1]), domain(Y,[3,4,5,6]), domain(Z,[1,6,7,8]),
X=Y, Y=Z.
X = 6,
Y = 6,
Z = 6
~~~~~
To demonstrate the use of the _Goals_ argument of
verify_attributes/3, we give an implementation of
freeze/2. We have to name it `myfreeze/2` in order to
avoid a name clash with the built-in predicate of the same name.
~~~~~
:- module(myfreeze, [myfreeze/2]).
:- use_module(library(atts)).
:- attribute frozen/1.
verify_attributes(Var, Other, Goals) :-
get_atts(Var, frozen(Fa)), !, % are we involved?
( var(Other) -> % must be attributed then
( get_atts(Other, frozen(Fb)) % has a pending goal?
-> put_atts(Other, frozen((Fa,Fb))) % rescue conjunction
; put_atts(Other, frozen(Fa)) % rescue the pending goal
),
Goals = []
; Goals = [Fa]
).
verify_attributes(_, _, []).
attribute_goal(Var, Goal) :- % interpretation as goal
get_atts(Var, frozen(Goal)).
myfreeze(X, Goal) :- put_atts(Fresh, frozen(Goal)), Fresh = X. ~~~~~
Assuming that this code lives in file myfreeze.yap,
we would use it via:
~~~~~
| ?- use_module(myfreeze).
| ?- myfreeze(X,print(bound(x,X))), X=2.
bound(x,2) % side effect
X = 2 % bindings
~~~~~
The two solvers even work together:
~~~~~
| ?- myfreeze(X,print(bound(x,X))), domain(X,[1,2,3]),
domain(Y,[2,10]), X=Y.
bound(x,2) % side effect
X = 2, % bindings
Y = 2
~~~~~
The two example solvers interact via bindings to shared attributed
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`.
@}
@{
### hProlog and SWI-Prolog style Attribute Declarations {#New_Style_Attribute_Declarations}
The following documentation is taken from the SWI-Prolog manual.
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 (built-in) 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.
~~~~~
:- 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),
v 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)
-> ord_intersection(Domain, Dom2, NewDomain),
( NewDomain == []
-> fail
; NewDomain = [Value]
-> Y = Value
; put_attr(Y, domain, NewDomain)
)
; var(Y)
-> put_attr( Y, domain, Domain )
; ord_memberchk(Y, Domain)
).
% Translate attributes from this module to residual goals %
attribute_goals(X) -->
{ get_attr(X, domain, List) },
[domain(X, List)].
~~~~~
Before explaining the code 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
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 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). The nonterminal `attribute_goals/3` is used to translate
remaining attributes to user-readable goals that, when executed, reinstate
these attributes.
@}
@{
### 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
sufficiently instantiated. This may result in a more "data-driven"
execution, or may be necessary to correctly implement extensions such
as negation by failure.
Initially, YAP used a separate mechanism for co-routining. Nowadays, YAP uses
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.
+ 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
- dif/2
- when/2
- frozen/2
@}
@}

391
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@ -1,391 +0,0 @@
Attributed Variables and Coroutingx
==================================
YAP supports attributed variables, originally developed at OFAI by
Christian Holzbaur. Attributes are a means of declaring that an
arbitrary term is a property for a variable. These properties can be
updated during forward execution. Moreover, the unification algorithm is
aware of attributed variables and will call user defined handlers when
trying to unify these variables.
Attributed variables provide an elegant abstraction over which one can
extend Prolog systems. Their main application so far has been in
implementing constraint handlers, such as Holzbaur's CLPQR, Fruewirth
and Holzbaur's CHR, and CLP(BN).
Different Prolog systems implement attributed variables in different
ways. Originally, YAP used the interface designed by SICStus
Prolog. This interface is still
available through the <tt>atts</tt> library, and is used by CLPBN.
From YAP-6.0.3 onwards we recommend using the hProlog, SWI style
interface. We believe that this design is easier to understand and
work with. Most packages included in YAP that use attributed
variables, such as CHR, CLP(FD), and CLP(QR), rely on the SWI-Prolog
interface.
+ @ref SICS_attributes
+ @ref sicsatts
+ @ref New_Style_Attribute_Declarations
+ @ref AttributedVariables_Builtins
+ @ref CohYroutining
### SICStus Style attribute declarations. {#SICS_attributes}
The YAP library `atts` implements attribute variables in the style of
SICStus Prolog. Attributed variables work as follows:
+ Each attribute must be declared beforehand. Attributes are described
as a functor with name and arity and are local to a module. Each
Prolog module declares its own sets of attributes. Different modules
may have attributes with the same name and arity.
+ The built-in put_atts/2 adds or deletes attributes to a
variable. The variable may be unbound or may be an attributed
variable. In the latter case, YAP discards previous values for the
attributes.
+ The built-in get_atts/2 can be used to check the values of
an attribute associated with a variable.
+ The unification algorithm calls the user-defined predicate
verify_attributes/3 before trying to bind an attributed
variable. Unification will resume after this call.
+ The user-defined predicate
<tt>attribute_goal/2</tt> converts from an attribute to a goal.
+ The user-defined predicate
<tt>project_attributes/2</tt> is used from a set of variables into a set of
constraints or goals. One application of <tt>project_attributes/2</tt> is in
the top-level, where it is used to output the set of
floundered constraints at the end of a query.
Attributes are compound terms associated with a variable. Each attribute
has a <em>name</em> which is <em>private</em> to the module in which the
attribute was defined. Variables may have at most one attribute with a
name. Attribute names are defined through the following declaration:
~~~~~
:- attribute AttributeSpec, ..., AttributeSpec.
~~~~~
where each _AttributeSpec_ has the form ( _Name_/ _Arity_).
One single such declaration is allowed per module _Module_.
Although the YAP module system is predicate based, attributes are local
to modules. This is implemented by rewriting all calls to the
built-ins that manipulate attributes so that attribute names are
preprocessed depending on the module. The `user:goal_expansion/3`
mechanism is used for this purpose.
The attribute manipulation predicates always work as follows:
+ The first argument is the unbound variable associated with
attributes,
+ 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.
The following three procedures are available to the user. Notice that
these built-ins are rewritten by the system into internal built-ins, and
that the rewriting process <em>depends</em> on the module on which the
built-ins have been invoked.
The user-predicate predicate verify_attributes/3 is called when
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:
Constraint solvers must be able to project a set of constraints to a set
of variables. This is useful when displaying the solution to a goal, but
may also be used to manipulate computations. The user-defined
project_attributes/2 is responsible for implementing this
projection.
The following examples are taken from the SICStus Prolog
manual. The sketches the implementation of a simple finite domain
`solver`. Note that an industrial strength solver would have to
provide a wider range of functionality and that it quite likely would
utilize a more efficient representation for the domains proper. The
module exports a single predicate `domain( _-Var_, _?Domain_)` which
associates _Domain_ (a list of terms) with _Var_. A variable can be
queried for its domain by leaving _Domain_ unbound.
We do not present here a definition for project_attributes/2.
Projecting finite domain constraints happens to be difficult.
~~~~~
:- module(domain, [domain/2]).
:- use_module(library(atts)).
:- use_module(library(ordsets), [
ord_intersection/3,
ord_intersect/2,
list_to_ord_set/2
]).
:- attribute dom/1.
verify_attributes(Var, Other, Goals) :-
get_atts(Var, dom(Da)), !, % are we involved?
( var(Other) -> % must be attributed then
( get_atts(Other, dom(Db)) -> % has a domain?
ord_intersection(Da, Db, Dc),
Dc = [El|Els], % at least one element
( Els = [] -> % exactly one element
Goals = [Other=El] % implied binding
; Goals = [],
put_atts(Other, dom(Dc))% rescue intersection
)
; Goals = [],
put_atts(Other, dom(Da)) % rescue the domain
)
; Goals = [],
ord_intersect([Other], Da) % value in domain?
).
verify_attributes(_, _, []). % unification triggered
% because of attributes
% in other modules
attribute_goal(Var, domain(Var,Dom)) :- % interpretation as goal
get_atts(Var, dom(Dom)).
domain(X, Dom) :-
var(Dom), !,
get_atts(X, dom(Dom)).
domain(X, List) :-
list_to_ord_set(List, Set),
Set = [El|Els], % at least one element
( Els = [] -> % exactly one element
X = El % implied binding
; put_atts(Fresh, dom(Set)),
X = Fresh % may call
% verify_attributes/3
).
~~~~~
Note that the _implied binding_ `Other=El` was deferred until after
the completion of `verify_attribute/3`. Otherwise, there might be a
danger of recursively invoking `verify_attribute/3`, which might bind
`Var`, which is not allowed inside the scope of `verify_attribute/3`.
Deferring unifications into the third argument of `verify_attribute/3`
effectively serializes the calls to `verify_attribute/3`.
Assuming that the code resides in the file domain.yap, we
can use it via:
~~~~~
| ?- use_module(domain).
~~~~~
Let's test it:
~~~~~
| ?- domain(X,[5,6,7,1]), domain(Y,[3,4,5,6]), domain(Z,[1,6,7,8]).
domain(X,[1,5,6,7]),
domain(Y,[3,4,5,6]),
domain(Z,[1,6,7,8]) ?
yes
| ?- domain(X,[5,6,7,1]), domain(Y,[3,4,5,6]), domain(Z,[1,6,7,8]),
X=Y.
Y = X,
domain(X,[5,6]),
domain(Z,[1,6,7,8]) ?
yes
| ?- domain(X,[5,6,7,1]), domain(Y,[3,4,5,6]), domain(Z,[1,6,7,8]),
X=Y, Y=Z.
X = 6,
Y = 6,
Z = 6
~~~~~
To demonstrate the use of the _Goals_ argument of
verify_attributes/3, we give an implementation of
freeze/2. We have to name it `myfreeze/2` in order to
avoid a name clash with the built-in predicate of the same name.
~~~~~
:- module(myfreeze, [myfreeze/2]).
:- use_module(library(atts)).
:- attribute frozen/1.
verify_attributes(Var, Other, Goals) :-
get_atts(Var, frozen(Fa)), !, % are we involved?
( var(Other) -> % must be attributed then
( get_atts(Other, frozen(Fb)) % has a pending goal?
-> put_atts(Other, frozen((Fa,Fb))) % rescue conjunction
; put_atts(Other, frozen(Fa)) % rescue the pending goal
),
Goals = []
; Goals = [Fa]
).
verify_attributes(_, _, []).
attribute_goal(Var, Goal) :- % interpretation as goal
get_atts(Var, frozen(Goal)).
myfreeze(X, Goal) :- put_atts(Fresh, frozen(Goal)), Fresh = X. ~~~~~
Assuming that this code lives in file myfreeze.yap,
we would use it via:
~~~~~
| ?- use_module(myfreeze).
| ?- myfreeze(X,print(bound(x,X))), X=2.
bound(x,2) % side effect
X = 2 % bindings
~~~~~
The two solvers even work together:
~~~~~
| ?- myfreeze(X,print(bound(x,X))), domain(X,[1,2,3]),
domain(Y,[2,10]), X=Y.
bound(x,2) % side effect
X = 2, % bindings
Y = 2
~~~~~
The two example solvers interact via bindings to shared attributed
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`.
@}
@{
### hProlog and SWI-Prolog style Attribute Declarations {#New_Style_Attribute_Declarations}
The following documentation is taken from the SWI-Prolog manual.
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 (built-in) 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.
~~~~~
:- 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),
v 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)
-> ord_intersection(Domain, Dom2, NewDomain),
( NewDomain == []
-> fail
; NewDomain = [Value]
-> Y = Value
; put_attr(Y, domain, NewDomain)
)
; var(Y)
-> put_attr( Y, domain, Domain )
; ord_memberchk(Y, Domain)
).
% Translate attributes from this module to residual goals %
attribute_goals(X) -->
{ get_attr(X, domain, List) },
[domain(X, List)].
~~~~~
Before explaining the code 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
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 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). The nonterminal `attribute_goals/3` is used to translate
remaining attributes to user-readable goals that, when executed, reinstate
these attributes.
@}
@{
### 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
sufficiently instantiated. This may result in a more "data-driven"
execution, or may be necessary to correctly implement extensions such
as negation by failure.
Initially, YAP used a separate mechanism for co-routining. Nowadays, YAP uses
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.
+ 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
- dif/2
- when/2
- frozen/2
See @ref attscorouts for more details.
@}
@}

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@ -1,5 +1,5 @@
The Foreign Code Interface {#fli_c_cxx}
===========================
### The Foreign Code Interface {#fli_c_cxx}
YAP provides the user with three facilities for writing
predicates in a language other than Prolog. Under Unix systems,
@ -17,8 +17,8 @@ being designed to work with the swig (www.swig.orgv) interface compiler.
+ @subpage YAPAsLibrary
### YAP original C-interface {#ChYInterface}
@{
#### YAP original C-interface {#ChYInterface}
Before describing in full detail how to interface to C code, we will examine
a brief example.
@ -48,13 +48,11 @@ void init_my_predicates()
The commands to compile the above file depend on the operating
system.
@}
@{
*/
/**
*
* Using the compiler:
@defgroup CallYAP Using the compiler:
Under Linux you should use:
@ -801,8 +799,6 @@ this is possible, _Goal_ will become invalid after executing
if (out == 0) return FALSE;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@copydoc real
The following functions complement _YAP_RunGoal_:
<ul>

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@ -1,5 +1,5 @@
The YAP Module system {#YAPModules}
=====================
### The YAP Module system {#YAPModules}
The YAP module system is based on the Quintus/SISCtus module
system ˜\cite quintus . In this design, modules are named collections of predicates,

2
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@ -14,7 +14,7 @@ YAP packages {#packages}
+ @subpage ProbLog1
+ @ref Python
x
+ @subpage raptor
+ @ref YAP-LBFGS

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@ -1,13 +1,13 @@
Running YAP {#run}
===========
#### Running YAP {#run}
We next describe how to invoke YAP in Unix systems.
[TOC]
### Running YAP Interactively {#Running_YAP_Interactively}
##### Running YAP Interactively {#Running_YAP_Interactively}
Most often you will want to use YAP in interactive mode. Assuming that

5
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@ -56,8 +56,8 @@ Please do refer to the SWI-Prolog home page:
for more information on SWI-Prolog and the SWI packages.
Compatibility with the C-Prolog interpreter {#ChYProlog}
-------------------------------------------
#### Compatibility with the C-Prolog interpreter {#ChYProlog}
YAP was designed so that most C-Prolog programs should run under YAP
without changes.
@ -180,5 +180,6 @@ known to still exist (please check Ulrich Neumerkel's page for more details):
operations, and handles floating-point errors only in some
architectures. Otherwise, YAP follows IEEE arithmetic.
<ul>
Please inform the authors on other incompatibilities that may still
exist.

10
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@ -460,9 +460,9 @@ errors can be controlled using `open/4` or `set_stream/2` (not
implemented). Initially the terminal stream write the characters using
Prolog escape sequences while other streams generate an I/O exception.
@{
=== @addgroup BOM BOM: Byte Order Mark
@addgroup BOM BOM: Byte Order Mark
@ingroup WideChars
From Stream Encoding, you may have got the impression that
@ -483,7 +483,11 @@ writing, writing a BOM can be requested using the option
UTF-32; otherwise the default is not to write a BOM. BOMs are not avaliable for ASCII and
ISO-LATIN-1.
= @addgroup Operators Summary of YAP Predefined Operators
@{
@}
@addgroup Operators Summary of YAP Predefined Operators
@ingroup YapSyntax
The Prolog syntax caters for operators of three main kinds:

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@ -17,7 +17,7 @@ Porto.
The manual is organised as follows:
+ @subpage INSTALL
+ @subpage INSTALL.md
+ @subpage run
@ -74,7 +74,7 @@ acknowledge the contributions from Ashwin Srinivasian.
YAP includes a number of extensions over the original Prolog
language.
+ @subpage atts.md
+ @subpage attributes.md
+ @ref Rational_Trees

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@ -1,564 +0,0 @@
YAP Syntax {#YAPSyntax}
====================
We will describe the syntax of YAP at two levels. We first will
describe the syntax for Prolog terms. In a second level we describe
the tokens from which Prolog terms are
built.
@defgroup Formal_Syntax Syntax of Terms
@ingroup YAPSyntax
Below, we describe the syntax of YAP terms from the different
classes of tokens defined above. The formalism used will be <em>BNF</em>,
extended where necessary with attributes denoting integer precedence or
operator type.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
term ----> subterm(1200) end_of_term_marker
subterm(N) ----> term(M) [M <= N]
term(N) ----> op(N, fx) subterm(N-1)
| op(N, fy) subterm(N)
| subterm(N-1) op(N, xfx) subterm(N-1)
| subterm(N-1) op(N, xfy) subterm(N)
| subterm(N) op(N, yfx) subterm(N-1)
| subterm(N-1) op(N, xf)
| subterm(N) op(N, yf)
term(0) ----> atom '(' arguments ')'
| '(' subterm(1200) ')'
| '{' subterm(1200) '}'
| list
| string
| number
| atom
| variable
arguments ----> subterm(999)
| subterm(999) ',' arguments
list ----> '[]'
| '[' list_expr ']'
list_expr ----> subterm(999)
| subterm(999) list_tail
list_tail ----> ',' list_expr
| ',..' subterm(999)
| '|' subterm(999)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Notes:
+ \a op(N,T) denotes an atom which has been previously declared with type
\a T and base precedence \a N.
+ Since ',' is itself a pre-declared operator with type \a xfy and
precedence 1000, is \a subterm starts with a '(', \a op must be
followed by a space to avoid ambiguity with the case of a functor
followed by arguments, e.g.:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ (a,b) [the same as '+'(','(a,b)) of arity one]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
versus
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+(a,b) [the same as '+'(a,b) of arity two]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
In the first rule for term(0) no blank space should exist between
\a atom and '('.
+
Each term to be read by the YAP parser must end with a single
dot, followed by a blank (in the sense mentioned in the previous
paragraph). When a name consisting of a single dot could be taken for
the end of term marker, the ambiguity should be avoided by surrounding the
dot with single quotes.
# @defgroup Tokens Prolog Tokens
@ingroup YAPSyntax
Prolog tokens are grouped into the following categories:
## @defgroup Numbers Numbers
@ingroup Tokens
Numbers can be further subdivided into integer and floating-point numbers.
### @defgroup Integers Integers
@ingroup Numbers
Integer numbers
are described by the following regular expression:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<integer> := {<digit>+<single-quote>|0{xXo}}<alpha_numeric_char>+
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
where {...} stands for optionality, \a + optional repetition (one or
more times), \a \\\<digit\\\> denotes one of the characters 0 ... 9, \a |
denotes or, and \a \\\<single-quote\\\> denotes the character "'". The digits
before the \a \\\<single-quote\\\> character, when present, form the number
basis, that can go from 0, 1 and up to 36. Letters from `A` to
`Z` are used when the basis is larger than 10.
Note that if no basis is specified then base 10 is assumed. Note also
that the last digit of an integer token can not be immediately followed
by one of the characters 'e', 'E', or '.'.
Following the ISO standard, YAP also accepts directives of the
form `0x` to represent numbers in hexadecimal base and of the form
`0o` to represent numbers in octal base. For usefulness,
YAP also accepts directives of the form `0X` to represent
numbers in hexadecimal base.
Example:
the following tokens all denote the same integer
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
10 2'1010 3'101 8'12 16'a 36'a 0xa 0o12
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Numbers of the form `0'a` are used to represent character
constants. So, the following tokens denote the same integer:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
0'd 100
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
YAP (version 6.3.4) supports integers that can fit
the word size of the machine. This is 32 bits in most current machines,
but 64 in some others, such as the Alpha running Linux or Digital
Unix. The scanner will read larger or smaller integers erroneously.
### @defgroup Floats Floats
@ingroup Numbers
Floating-point numbers are described by:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<float> := <digit>+{<dot><digit>+}
<exponent-marker>{<sign>}<digit>+
|<digit>+<dot><digit>+
{<exponent-marker>{<sign>}<digit>+}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
where \a \\\<dot\\\> denotes the decimal-point character '.',
\a \\\<exponent-marker\\\> denotes one of 'e' or 'E', and \a \\\<sign\\\> denotes
one of '+' or '-'.
Examples:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
10.0 10e3 10e-3 3.1415e+3
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Floating-point numbers are represented as a double in the target
machine. This is usually a 64-bit number.
## Strings @defgroup Strings Character Strings
Strings are described by the following rules:
~~~~
string --> " string_quoted_characters "
string --> ` string_quoted_characters `
string_quoted_characters --> '"' '"' string_quoted_characters
string_quoted_characters --> '\'
escape_sequence string_quoted_characters
string_quoted_characters -->
string_character string_quoted_characters
escape_sequence --> 'a' | 'b' | 'r' | 'f' | 't' | 'n' | 'v'
escape_sequence --> '\' | '"' | ''' | '`'
escape_sequence --> at_most_3_octal_digit_seq_char '\'
escape_sequence --> 'x' at_most_2_hexa_digit_seq_char '\'
~~~~
where `string_character` is any character except the double quote (back quote)
and escape characters.
YAP supports four different textual elements:
+ Atoms, mentioned above, are textual representations of symbols, that are interned in the
data-base. They are stored either in ISO-LATIN-1 (first 256 code points), or as UTF-32.
+ Strings are atomic representations of text. The back-quote character is used to identify these objects in the program. Strings exist as stack objects, in the same way as other Prolog terms. As Prolog unification cannot be used to manipulate strings, YAP includes built-ins such as string_arg/3, sub_string/5, or string_concat to manipulate them efficiently. Strings are stored as opaque objects containing a
+ Lists of codes represent text as a list of numbers, where each number is a character code. A string of _N_ bytes requires _N_ pairs, that is _2N_ cells, leading to a total of 16 bytes per character on 64 byte machines. Thus, they are a very expensive, but very flexible representation, as one can use unification to construct and access string elements.
+ Lists of atoms represent text as a list of atoms, where each number has a single character code. A string of _N_ bytes also requires _2N_ pairs. They have similar properties to lists of codes.
The flags `double_quotes` and `backquoted_string` change the interpretation of text strings, they can take the
values `atom`, `string`, `codes`, and `chars`.
Examples:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"" "a string" "a double-quote:"""
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The first string is an empty string, the last string shows the use of
double-quoting.
Escape sequences can be used to include the non-printable characters
`a` (alert), `b` (backspace), `r` (carriage return),
`f` (form feed), `t` (horizontal tabulation), `n` (new
line), and `v` (vertical tabulation). Escape sequences also be
include the meta-characters `\\`, `"`, `'`, and
```. Last, one can use escape sequences to include the characters
either as an octal or hexadecimal number.
The next examples demonstrates the use of escape sequences in YAP:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"\x0c\" "\01\" "\f" "\\"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The first three examples return a list including only character 12 (form
feed). The last example escapes the escape character.
Escape sequences were not available in C-Prolog and in original
versions of YAP up to 4.2.0. Escape sequences can be disabled by using:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:- yap_flag(character_escapes,false).
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
## @addgroup Atoms Atoms
@ingroup Tokens
Atoms are defined by one of the following rules:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
atom --> solo-character
atom --> lower-case-letter name-character*
atom --> symbol-character+
atom --> single-quote single-quote
atom --> ''' atom_quoted_characters '''
atom_quoted_characters --> ''' ''' atom_quoted_characters
atom_quoted_characters --> '\' atom_sequence string_quoted_characters
atom_quoted_characters --> character string_quoted_characters
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
where:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<solo-character> denotes one of: ! ;
<symbol-character> denotes one of: # & * + - . / : <
= > ? @ \ ^ ~ `
<lower-case-letter> denotes one of: a...z
<name-character> denotes one of: _ a...z A...Z 0....9
<single-quote> denotes: '
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
and `string_character` denotes any character except the double quote
and escape characters. Note that escape sequences in strings and atoms
follow the same rules.
Examples:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a a12x '$a' ! => '1 2'
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Version `4.2.0` of YAP removed the previous limit of 256
characters on an atom. Size of an atom is now only limited by the space
available in the system.
## @addgroup Variables Variables
@ingroup Tokens
Variables are described by:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<variable-starter><variable-character>+
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
where
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<variable-starter> denotes one of: _ A...Z
<variable-character> denotes one of: _ a...z A...Z
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If a variable is referred only once in a term, it needs not to be named
and one can use the character `_` to represent the variable. These
variables are known as anonymous variables. Note that different
occurrences of `_` on the same term represent <em>different</em>
anonymous variables.
## @addgroup Punctuation_Tokens Punctuation Tokens
@ingroup Tokens
Punctuation tokens consist of one of the following characters:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
( ) , [ ] { } |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
These characters are used to group terms.
@subsection Layout Layout
Any characters with ASCII code less than or equal to 32 appearing before
a token are ignored.
All the text appearing in a line after the character \a % is taken to
be a comment and ignored (including \a %). Comments can also be
inserted by using the sequence `/\*` to start the comment and
`\*` followed by `/` to finish it. In the presence of any sequence of comments or
layout characters, the YAP parser behaves as if it had found a
single blank character. The end of a file also counts as a blank
character for this purpose.
## @addgroup WideChars Encoding Wide Character Support
@ingroup YAPSyntax
YAP now implements a SWI-Prolog compatible interface to wide
characters and the Universal Character Set (UCS). The following text
was adapted from the SWI-Prolog manual.
YAP now supports wide characters, characters with character
codes above 255 that cannot be represented in a single byte.
<em>Universal Character Set</em> (UCS) is the ISO/IEC 10646 standard
that specifies a unique 31-bits unsigned integer for any character in
any language. It is a superset of 16-bit Unicode, which in turn is
a superset of ISO 8859-1 (ISO Latin-1), a superset of US-ASCII. UCS
can handle strings holding characters from multiple languages and
character classification (uppercase, lowercase, digit, etc.) and
operations such as case-conversion are unambiguously defined.
For this reason YAP, following SWI-Prolog, has two representations for
atoms. If the text fits in ISO Latin-1, it is represented as an array
of 8-bit characters. Otherwise the text is represented as an array of
wide chars, which may take 16 or 32 bits. This representational issue
is completely transparent to the Prolog user. Users of the foreign
language interface sometimes need to be aware of these issues though. Notice that this will likely
change in the future, we probably will use an UTF-8 based representation.
Character coding comes into view when characters of strings need to be
read from or written to file or when they have to be communicated to
other software components using the foreign language interface. In this
section we only deal with I/O through streams, which includes file I/O
as well as I/O through network sockets.
== @addgroup Stream_Encoding Wide character encodings on streams
@ingroup WideChars
The UCS standard describes all possible characters (or code points, as they include
ideograms, ligatures, and other symbols). The current version, Unicode 8.0, allows
code points up to 0x10FFFF, and thus allows for 1,114,112 code points. See [Unicode Charts](http://unicode.org/charts/) for the supported languages.
Notice that most symbols are rarely used. Encodings represent the Unicode characters in a way
that is more suited for communication. The most popular encoding, especially in the context of the web and in the Unix/Linux/BSD/Mac communities, is
UTF-8. UTF-8 is compact and as it uses bytes, does not have different endianesses.
Bytes 0...127 represent simply the corresponding US-ASCII
character, while bytes 128...255 are used for multi-byte
encoding of characters placed higher in the UCS space.
Especially on
MS-Windows and Java the 16-bit Unicode standard, represented by pairs of bytes is
also popular. Originally, Microsoft supported a UCS-2 with 16 bits that
could represent only up to 64k characters. This was later extended to support the full
Unicode, we will call the latter version UTF-16. The extension uses a hole in the first 64K code points. Characters above 0xFFFF are divided into two 2-byte words, each one in that hole. There are two versions of UTF-16: big and low
endian. By default, UTF-16 is big endian, in practice most often it is used on Intel
hardware that is naturally little endian.
UTF-32, often called UCS-4, provides a natural interface where a code point is coded as
four octets. Unfortunately, it is also more expensive, so it is not as widely used.
Last, other encodings are also commonly used. One such legacy encoding is ISO-LATIN-1, that
supported latin based languages in western europe. YAP currently uses either ISO-LATIN-1 or UTF-32
internally.
Prolog supports the default encoding used by the Operating System,
Namely, YAP checks the variables LANG, LC_ALL and LC_TYPE. Say, if at boot YAP detects that the
environment variable `LANG` ends in "UTF-8", this encoding is
assumed. Otherwise, the default is `text` and the translation is
left to the wide-character functions of the C-library (note that the
Prolog native UTF-8 mode is considerably faster than the generic
`mbrtowc()` one).
Prolog allows the encoding to be specified explicitly in
load_files/2 for loading Prolog source with an alternative
encoding, `open/4` when opening files or using `set_stream/2` on
any open stream (not yet implemented). For Prolog source files we also
provide the `encoding/1` directive that can be used to switch
between encodings that are compatible to US-ASCII (`ascii`,
`iso_latin_1`, `utf8` and many locales).
For
additional information and Unicode resources, please visit the
[unicode](http://www.unicode.org/) organization web page.
YAP currently defines and supports the following encodings:
+ `octet`
Default encoding for <em>binary</em> streams. This causes
the stream to be read and written fully untranslated.
+ `ascii` or `US_ASCII`
7-bit encoding in 8-bit bytes. Equivalent to `iso_latin_1`,
but generates errors and warnings on encountering values above
127.
+ `iso_latin_1` or `ISO-8859-1`
8-bit encoding supporting many western languages. This causes
the stream to be read and written fully untranslated.
+ `text`
C-library default locale encoding for text files. Files are read and
written using the C-library functions `mbrtowc()` and
`wcrtomb()`. This may be the same as one of the other locales,
notably it may be the same as `iso_latin_1` for western
languages and `utf8` in a UTF-8 context.
+ `utf8`, `iso_utf8`, or `UTF-8``
Multi-byte encoding of the full Unicode 8, compatible to `ascii` .
See above.
+ `unicode_be` or `UCS-2BE`
Unicode Big Endian. Reads input in pairs of bytes, most
significant byte first. Can only represent 16-bit characters.
+ `unicode_le` or `UCS-2LE`
Unicode Little Endian. Reads input in pairs of bytes, least
significant byte first. Can only represent 16-bit characters.
+ `utf16_le` or `UTF-16LE` (experimental)
UTF-16 Little Endian. Reads input in pairs of bytes, least
significant byte first. Can represent the full Unicode.
+ `utf16_le` or `UTF-16BE` (experimental)
Unicode Big Endian. Reads input in pairs of bytes, least
significant byte first. Can represent the full Unicode.
+ `utf32_le` or `UTF-32LE` (experimental)
UTF-16 Little Endian. Reads input in pairs of bytes, least
significant byte first. Can represent the full Unicode.
+ `utf32_le` or `UTF-32BE` (experimental)
Unicode Big Endian. Reads input in pairs of bytes, least
significant byte first. Can only represent 16-bit characters.
Note that not all encodings can represent all characters. This implies
that writing text to a stream may cause errors because the stream
cannot represent these characters. The behaviour of a stream on these
errors can be controlled using `open/4` or `set_stream/2` (not
implemented). Initially the terminal stream write the characters using
Prolog escape sequences while other streams generate an I/O exception.
=== @addgroup BOM BOM: Byte Order Mark
@ingroup WideChars
From Stream Encoding, you may have got the impression that
text-files are complicated. This section deals with a related topic,
making live often easier for the user, but providing another worry to
the programmer. *BOM* or <em>Byte Order Marker</em> is a technique
for identifying Unicode text-files as well as the encoding they
use. Please read the [W3C](https://www.w3.org/International/questions/qa-byte-order-mark.en.php]
page for a detailed explanation of byte-order marks.
BOMa are necessary on multi-byte encodings, such as UTF-16 and UTF-32. There is a BOM for UTF-8, but it is rarely used.
The BOM is handled by the open/4 predicate. By default, text-files are
probed for the BOM when opened for reading. If a BOM is found, the
encoding is set accordingly and the property `bom(true)` is
available through stream_property/2. When opening a file for
writing, writing a BOM can be requested using the option
`bom(true)` with `open/4`. YAP will parse an UTF-8 file for a BOM only if explicitly required to do so. Do notice that YAP will write a BOM by default on UTF-16 (including UCS-2) and
UTF-32; otherwise the default is not to write a BOM. BOMs are not avaliable for ASCII and
ISO-LATIN-1.
= @addgroup Operators Summary of YAP Predefined Operators
@ingroup YapSyntax
The Prolog syntax caters for operators of three main kinds:
+ prefix;
+ infix;
+ postfix.
Each operator has precedence in the range 1 to 1200, and this
precedence is used to disambiguate expressions where the structure of the
term denoted is not made explicit using brackets. The operator of higher
precedence is the main functor.
If there are two operators with the highest precedence, the ambiguity
is solved analyzing the types of the operators. The possible infix types are:
_xfx_, _xfy_, and _yfx_.
With an operator of type _xfx_ both sub-expressions must have lower
precedence than the operator itself, unless they are bracketed (which
assigns to them zero precedence). With an operator type _xfy_ only the
left-hand sub-expression must have lower precedence. The opposite happens
for _yfx_ type.
A prefix operator can be of type _fx_ or _fy_.
A postfix operator can be of type _xf_ or _yf_.
The meaning of the notation is analogous to the above.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a + b * c
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
means
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a + (b * c)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
as + and \* have the following types and precedences:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:-op(500,yfx,'+').
:-op(400,yfx,'*').
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Now defining
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:-op(700,xfy,'++').
:-op(700,xfx,'=:=').
a ++ b =:= c
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
means
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a ++ (b =:= c)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The following is the list of the declarations of the predefined operators:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:-op(1200,fx,['?-', ':-']).
:-op(1200,xfx,[':-','-->']).
:-op(1150,fx,[block,dynamic,mode,public,multifile,meta_predicate,
sequential,table,initialization]).
:-op(1100,xfy,[';','|']).
:-op(1050,xfy,->).
:-op(1000,xfy,',').
:-op(999,xfy,'.').
:-op(900,fy,['\+', not]).
:-op(900,fx,[nospy, spy]).
:-op(700,xfx,[@>=,@=<,@<,@>,<,=,>,=:=,=\=,\==,>=,=<,==,\=,=..,is]).
:-op(500,yfx,['\/','/\','+','-']).
:-op(500,fx,['+','-']).
:-op(400,yfx,['<<','>>','//','*','/']).
:-op(300,xfx,mod).
:-op(200,xfy,['^','**']).
:-op(50,xfx,same).
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@}

12
include/YapInterface.h
View File

@ -21,10 +21,9 @@
@addtogroup ChYInterface
@{
\
@brief Core interface to YAP.
@brief C-Interface to YAP.
@toc
The following routines export the YAP internals and architecture.
*/
@ -70,10 +69,10 @@ __BEGIN_DECLS
/**
* X_API macro
*
* brif
*
* @param _WIN32
* @brief declares the symbol as to be exported/imported from a
* DLL. It is mostly ignored in Linux, but honored in WIN32.
*
* @return
*/
@ -81,6 +80,7 @@ __BEGIN_DECLS
/* Primitive Functions */
// Basic operation that follows a pointer chain.
#define YAP_Deref(t) (t)
X_API

1
library/random.yap
View File

@ -222,4 +222,5 @@ getrand(rand(X,Y,Z)) :-
getrand(X,Y,Z).
/** @} */
/** @} */

7
library/system.yap
View File

@ -531,7 +531,7 @@ environ_split([61|SVal], [], SVal) :- !.
environ_split([C|S],[C|SNa],SVal) :-
environ_split(S,SNa,SVal).
/** @pred exec(+ _Command_, _StandardStreams_,- _PID_)
/** @pred exec(+ Command, StandardStreams, -PID)
*
*
*
@ -610,7 +610,7 @@ close_temp_streams([S|Ss]) :-
close(S),
close_temp_streams(Ss).
/** @pred popen(+ _Command_, + _TYPE_, - _Stream_)
/** @pred popen( +Command, +TYPE, -Stream)
* Provides the functionaluty of the Unix <tt>popen</tt> function. It
* opens a process by creating a pipe, forking and invoking _Command_ on
@ -805,7 +805,8 @@ rename_file(F0, F) :-
rename_file(F0, F, Error),
handle_system_internal(Error, off, rename_file(F0, F)).
/** @pred system(+ _S_)
/**
* @pred system(+ _S_)
Passes command _S_ to the Bourne shell (on UNIX environments) or the
current command interpreter in WIN32 environments.

8
mkdocs/mkdocs.yml Normal file
View File

@ -0,0 +1,8 @@
site_name: 'YAP'
theme: 'readthedocs'
plugins:
- search
- awesome-pages:
filename: .index
disable_auto_arrange_index: false
collapse_single_pages: true

6
os/format.c
View File

@ -1078,11 +1078,13 @@ static Int with_output_to(USES_REGS1) {
Yap_Error(INSTANTIATION_ERROR, tin, "with_output_to/3");
return false;
}
if (IsApplTerm(tin) && (f = FunctorOfTerm(tin)) &&
(f == FunctorAtom || f == FunctorString || f == FunctorCodes1 ||
if (IsApplTerm(tin) && (f = FunctorOfTerm(tin))) {
if(f == FunctorAtom || f == FunctorString || f == FunctorCodes1 ||
f == FunctorCodes || f == FunctorChars1 || f == FunctorChars)) {
output_stream = Yap_OpenBufWriteStream(PASS_REGS1);
my_mem_stream = true;
}
} else {
/* needs to change LOCAL_c_output_stream for write */
output_stream = Yap_CheckStream(ARG1, Output_Stream_f, "format/3");

2
pl/arrays.yap
View File

@ -21,7 +21,7 @@
@addtogroup YAPArraysPl Prolog Support for seeing terms as arrays and for data-base arrays of objects
@ingroupp YAPArrays
@ingroup YAPArrays
@{
*/

3
pl/checker.yap
View File

@ -156,7 +156,8 @@ no_style_check(-multiple) :-
no_style_check([]).
no_style_check([H|T]) :- no_style_check(H), no_style_check(T).
/** @pred discontiguous(+ _G_) is iso
/**
* @pred discontiguous(+ G) is iso, directive
Avoid warnings from the sytax checker.
Declare that the predicate _G_ or list of predicates are discontiguous

2
pl/flags.yap
View File

@ -15,7 +15,7 @@
* *
*************************************************************************/
/**
* @file flags.yap
* @file pl/flags.yap
*
* @defgroup YAPFlags Yap Flags
*

4
pl/hacks.yap
View File

@ -17,7 +17,8 @@
*************************************************************************/
/**
* @file hacks.yap
DD%% @file pl/hacks.yap
* @file hacks.yap
* @author VITOR SANTOS COSTA <vsc@VITORs-MBP-2.lan>
* @date Thu Oct 19 12:02:56 2017
*
@ -28,7 +29,6 @@
*
*/
%% @file pl/hacks.yap
:- module('$hacks',
[display_stack_info/4,

2
pl/metadecls.yap
View File

@ -1,6 +1,6 @@
/**
* @file metadecl.yap
* @file metadecls.yap
* @author VITOR SANTOS COSTA <vsc@vcosta-laptop.dcc.fc.up.pt>
* @date Sat Apr 7 03:08:03 2018
*

2
pl/newmod.yap
View File

@ -27,8 +27,6 @@ module(N) :-
'$do_error'(type_error(atom,N),module(N)).
/**
\pred module(+ Module:atom, +ExportList:list) is directive
define a new module
This directive defines the file where it appears as a _module file_;
it must be the first declaration in the file. _Module_ must be an

4
swi/library/predopts.pl
View File

@ -32,8 +32,8 @@
]).
:- multifile
predicate_options:option_decl/3,
predicate_options:pred_option/3.
option_decl/3,
:pred_option/3.
:- multifile % provided by library(predicate_options)
system:predicate_option_type/2,
system:predicate_option_mode/2.