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<h1 id="sec:glossary"><a id="sec:D"><span class="sec-nr">D</span> <span class="sec-title">Glossary 
of Terms</span></a></h1>

<a id="sec:glossary"></a>

<dl class="latex">
<dt><a id="gloss:anonymou"><strong>anonymous [variable]</strong></a></dt>
<dd class="defbody">
<a id="idx:anonymousvariable:2073"></a><a id="idx:variableanonymous:2074"></a>The 
variable <code>_</code> is called the <a class="gloss" href="glossary.html#gloss:anonymou">anonymous</a> 
variable. Multiple occurrences of <code>_</code> in a single <a class="gloss" href="glossary.html#gloss:term">term</a> 
are not <a class="gloss" href="glossary.html#gloss:shared">shared</a>.</dd>
<dt><a id="gloss:argument"><strong>arguments</strong></a></dt>
<dd class="defbody">
Arguments are <a class="gloss" href="glossary.html#gloss:term">terms</a> 
that appear in a <a class="gloss" href="glossary.html#gloss:compound">compound</a> <a class="gloss" href="glossary.html#gloss:term">term</a>. <var>A1</var> 
and <var>a2</var> are the first and second argument of the term
<code>myterm(A1, a2)</code>.</dd>
<dt><a id="gloss:arity"><strong>arity</strong></a></dt>
<dd class="defbody">
<a id="idx:arity:2075"></a>Argument count (= number of arguments) of a <a class="gloss" href="glossary.html#gloss:compound">compound</a> <a class="gloss" href="glossary.html#gloss:term">term</a>.</dd>
<dt><a id="gloss:assert"><strong>assert</strong></a></dt>
<dd class="defbody">
<a id="idx:assert:2076"></a>Add a <a class="gloss" href="glossary.html#gloss:clause">clause</a> 
to a <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>. 
Clauses can be added at either end of the clause-list of a <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>. 
See <a id="idx:asserta1:2077"></a><a class="pred" href="db.html#asserta/1">asserta/1</a> 
and <a id="idx:assertz1:2078"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>.</dd>
<dt><a id="gloss:atom"><strong>atom</strong></a></dt>
<dd class="defbody">
<a id="idx:atom:2079"></a>Textual constant. Used as name for <a class="gloss" href="glossary.html#gloss:compound">compound</a> 
terms, to represent constants or text.</dd>
<dt><a id="gloss:backtracking"><strong>backtracking</strong></a></dt>
<dd class="defbody">
<a id="idx:backtracking:2080"></a>Search process used by Prolog. If a 
predicate offers multiple
<a class="gloss" href="glossary.html#gloss:clause">clauses</a> to solve 
a <a class="gloss" href="glossary.html#gloss:goal">goal</a>, they are 
tried one-by-one until one <a class="gloss" href="glossary.html#gloss:succeed">succeeds</a>. 
If a subsequent part of the proof is not satisfied with the resulting <a class="gloss" href="glossary.html#gloss:variable">variable</a> <a class="gloss" href="glossary.html#gloss:binding">binding</a>, 
it may ask for an alternative <a class="gloss" href="glossary.html#gloss:solution">solution</a> 
(= <a class="gloss" href="glossary.html#gloss:binding">binding</a> of 
the <a class="gloss" href="glossary.html#gloss:variable">variables</a>), 
causing Prolog to reject the previously chosen <a class="gloss" href="glossary.html#gloss:clause">clause</a> 
and try the next one.</dd>
<dt><a id="gloss:binding"><strong>binding [of a variable]</strong></a></dt>
<dd class="defbody">
<a id="idx:binding:2081"></a>Current value of the <a class="gloss" href="glossary.html#gloss:variable">variable</a>. 
See also <a class="gloss" href="glossary.html#gloss:backtracking">backtracking</a> 
and
<a class="gloss" href="glossary.html#gloss:query">query</a>.</dd>
<dt><a id="gloss:built-in"><strong>built-in [predicate]</strong></a></dt>
<dd class="defbody">
<a id="idx:builtinpredicate:2082"></a>Predicate that is part of the 
Prolog system. Built-in predicates cannot be redefined by the user, 
unless this is overruled using
<a id="idx:redefinesystempredicate1:2083"></a><a class="pred" href="db.html#redefine_system_predicate/1">redefine_system_predicate/1</a>.</dd>
<dt><a id="gloss:body"><strong>body</strong></a></dt>
<dd class="defbody">
<a id="idx:body:2084"></a>Part of a <a class="gloss" href="glossary.html#gloss:clause">clause</a> 
behind the <a class="gloss" href="glossary.html#gloss:neck">neck</a> 
operator (<code><code>:-</code></code>).</dd>
<dt><a id="gloss:choice-point"><strong>choice point</strong></a></dt>
<dd class="defbody">
<a id="idx:choicepoint:2085"></a>A <a class="gloss" href="glossary.html#gloss:choice-point">choice point</a> 
represents a choice in the search for a <a class="gloss" href="glossary.html#gloss:solution">solution</a>. 
Choice points are created if multiple clauses match a <a class="gloss" href="glossary.html#gloss:query">query</a> 
or using disjunction (<a class="pred" href="control.html#;/2">;/2</a>). 
On <a class="gloss" href="glossary.html#gloss:backtracking">backtracking</a>, 
the execution state of the most recent <a class="gloss" href="glossary.html#gloss:choice-point">choice point</a> 
is restored and search continues with the next alternative (i.e., next 
clause or second branch of
<a class="pred" href="control.html#;/2">;/2</a>).</dd>
<dt><a id="gloss:clause"><strong>clause</strong></a></dt>
<dd class="defbody">
<a id="idx:clause:2086"></a>`Sentence' of a Prolog program. A <a class="gloss" href="glossary.html#gloss:clause">clause</a> 
consists of a <a class="gloss" href="glossary.html#gloss:head">head</a> 
and
<a class="gloss" href="glossary.html#gloss:body">body</a> separated by 
the <a class="gloss" href="glossary.html#gloss:neck">neck</a> operator (<code><code>:-</code></code>) 
or it is a
<a class="gloss" href="glossary.html#gloss:fact">fact</a>. For example:

<pre class="code">
parent(X) :-
        father(X, _).
</pre>

<p>Expressed as ``X is a parent if X is a father of someone''. See also
<a class="gloss" href="glossary.html#gloss:variable">variable</a> and <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>.</dd>
<dt><a id="gloss:compile"><strong>compile</strong></a></dt>
<dd class="defbody">
Process where a Prolog <a class="gloss" href="glossary.html#gloss:program">program</a> 
is translated to a sequence of instructions. See also <a class="gloss" href="glossary.html#gloss:interpreted">interpreted</a>. 
SWI-Prolog always compiles your program before executing it.</dd>
<dt><a id="gloss:compound"><strong>compound [term]</strong></a></dt>
<dd class="defbody">
<a id="idx:compound:2087"></a>Also called <a class="gloss" href="glossary.html#gloss:structure">structure</a>. 
It consists of a name followed by <var>N</var>
<a class="gloss" href="glossary.html#gloss:argument">arguments</a>, each 
of which are <a class="gloss" href="glossary.html#gloss:term">terms</a>. <var>N</var> 
is called the
<a class="gloss" href="glossary.html#gloss:arity">arity</a> of the term.</dd>
<dt><a id="gloss:context-module"><strong>context module</strong></a></dt>
<dd class="defbody">
<a id="idx:contextmodule:2088"></a><a id="idx:modulecontex:2089"></a>If 
a <a class="gloss" href="glossary.html#gloss:term">term</a> is referring 
to a <a class="gloss" href="glossary.html#gloss:predicate">predicate</a> 
in a <a class="gloss" href="glossary.html#gloss:module">module</a>, the
<a class="gloss" href="glossary.html#gloss:context-module">context module</a> 
is used to find the target module. The context module of a <a class="gloss" href="glossary.html#gloss:goal">goal</a> 
is the module in which the <a class="gloss" href="glossary.html#gloss:predicate">predicate</a> 
is defined, unless this <a class="gloss" href="glossary.html#gloss:predicate">predicate</a> 
is <a class="gloss" href="glossary.html#gloss:module-transparent">module transparent</a>, 
in which case the <a class="gloss" href="glossary.html#gloss:context-module">context module</a> 
is inherited from the parent
<a class="gloss" href="glossary.html#gloss:goal">goal</a>. See also <a id="idx:moduletransparent1:2090"></a><a class="pred" href="ctxmodule.html#module_transparent/1">module_transparent/1</a> 
and <a class="gloss" href="glossary.html#gloss:meta-predicate">meta-predicate</a>.</dd>
<dt><a id="gloss:det"><strong>det [determinism]</strong></a></dt>
<dd class="defbody">
<a id="idx:det:2091"></a>Short for <a class="gloss" href="glossary.html#gloss:deterministic">deterministic</a>.</dd>
<dt><a id="gloss:determinism"><strong>determinism</strong></a></dt>
<dd class="defbody">
<a id="idx:determinism:2092"></a>How many solutions a <a class="gloss" href="glossary.html#gloss:goal">goal</a> 
can provide. Values are `nondet' (zero to infinite), `multi' (one to 
infinite), `det' (exactly one) and `semidet' (zero or one).</dd>
<dt><a id="gloss:deterministic"><strong>deterministic</strong></a></dt>
<dd class="defbody">
<a id="idx:deterministic:2093"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a> 
is <a class="gloss" href="glossary.html#gloss:deterministic">deterministic</a> 
if it succeeds exactly one time without leaving a <a class="gloss" href="glossary.html#gloss:choice-point">choice point</a>.</dd>
<dt><a id="gloss:dynamic"><strong>dynamic [predicate]</strong></a></dt>
<dd class="defbody">
<a id="idx:dynamicpredicate:2094"></a><a id="idx:predicatedynamic:2095"></a>A <a class="gloss" href="glossary.html#gloss:dynamic">dynamic</a> 
predicate is a predicate to which <a class="gloss" href="glossary.html#gloss:clause">clauses</a> 
may be
<a class="gloss" href="glossary.html#gloss:assert">assert</a>ed and from 
which <a class="gloss" href="glossary.html#gloss:clause">clauses</a> may 
be <a class="gloss" href="glossary.html#gloss:retract">retract</a>ed 
while the program is running. See also <a class="gloss" href="glossary.html#gloss:update-view">update view</a>.</dd>
<dt><a id="gloss:exported"><strong>exported [predicate]</strong></a></dt>
<dd class="defbody">
<a id="idx:exportedpredicate:2096"></a><a id="idx:predicateexported:2097"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a> 
is said to be <a class="gloss" href="glossary.html#gloss:exported">exported</a> 
from a <a class="gloss" href="glossary.html#gloss:module">module</a> if 
it appears in the <a class="gloss" href="glossary.html#gloss:public-list">public list</a>. 
This implies that the predicate can be <a class="gloss" href="glossary.html#gloss:imported">imported</a> 
into another module to make it visible there. See also <a id="idx:usemodule12:2098"></a><span class="pred-ext">use_module/[1,2]</span>.</dd>
<dt><a id="gloss:fact"><strong>fact</strong></a></dt>
<dd class="defbody">
<a id="idx:fact:2099"></a><a class="gloss" href="glossary.html#gloss:clause">Clause</a> 
without a <a class="gloss" href="glossary.html#gloss:body">body</a>. 
This is called a fact because, interpreted as logic, there is no 
condition to be satisfied. The example below states <code>john</code> is 
a person.

<pre class="code">
person(john).
</pre>

</dd>
<dt><a id="gloss:fail"><strong>fail</strong></a></dt>
<dd class="defbody">
A <a class="gloss" href="glossary.html#gloss:goal">goal</a> is said to 
haved failed if it could not be <a class="gloss" href="glossary.html#gloss:prove">proven</a>.</dd>
<dt><a id="gloss:float"><strong>float</strong></a></dt>
<dd class="defbody">
Computer's crippled representation of a real number. Represented as 
`IEEE double'.</dd>
<dt><a id="gloss:foreign"><strong>foreign</strong></a></dt>
<dd class="defbody">
Computer code expressed in languages other than Prolog. SWI-Prolog can 
only cooperate directly with the C and C++ computer languages.</dd>
<dt><a id="gloss:functor"><strong>functor</strong></a></dt>
<dd class="defbody">
<a id="idx:functor:2100"></a>Combination of name and <a class="gloss" href="glossary.html#gloss:arity">arity</a> 
of a <a class="gloss" href="glossary.html#gloss:compound">compound</a> 
term. The term
<code>foo(a, b, c)</code> is said to be a term belonging to the functor 
foo/3 . foo/0 is used to refer to the <a class="gloss" href="glossary.html#gloss:atom">atom</a>
<code>foo</code>.</dd>
<dt><a id="gloss:goal"><strong>goal</strong></a></dt>
<dd class="defbody">
<a id="idx:goal:2101"></a><a id="idx:query:2102"></a>Question stated to 
the Prolog engine. A <a class="gloss" href="glossary.html#gloss:goal">goal</a> 
is either an <a class="gloss" href="glossary.html#gloss:atom">atom</a> 
or a <a class="gloss" href="glossary.html#gloss:compound">compound</a> 
term. A <a class="gloss" href="glossary.html#gloss:goal">goal</a> either 
succeeds, in which case the
<a class="gloss" href="glossary.html#gloss:variable">variables</a> in 
the <a class="gloss" href="glossary.html#gloss:compound">compound</a> 
terms have a <a class="gloss" href="glossary.html#gloss:binding">binding</a>, 
or it <a class="gloss" href="glossary.html#gloss:fail">fails</a> if 
Prolog fails to prove it.</dd>
<dt><a id="gloss:hashing"><strong>hashing</strong></a></dt>
<dd class="defbody">
<a id="idx:hashing:2103"></a><a class="gloss" href="glossary.html#gloss:indexing">Indexing</a> 
technique used for quick lookup.</dd>
<dt><a id="gloss:head"><strong>head</strong></a></dt>
<dd class="defbody">
<a id="idx:head:2104"></a>Part of a <a class="gloss" href="glossary.html#gloss:clause">clause</a> 
before the <a class="gloss" href="glossary.html#gloss:neck">neck</a> 
operator (<code><code>:-</code></code>). This is an <a class="gloss" href="glossary.html#gloss:atom">atom</a> 
or <a class="gloss" href="glossary.html#gloss:compound">compound</a> 
term.</dd>
<dt><a id="gloss:imported"><strong>imported [predicate]</strong></a></dt>
<dd class="defbody">
<a id="idx:importedpredicate:2105"></a><a id="idx:predicateimported:2106"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a> 
is said to be <a class="gloss" href="glossary.html#gloss:imported">imported</a> 
into a <a class="gloss" href="glossary.html#gloss:module">module</a> if 
it is defined in another <a class="gloss" href="glossary.html#gloss:module">module</a> 
and made available in this <a class="gloss" href="glossary.html#gloss:module">module</a>. 
See also <a class="sec" href="modules.html">chapter 6</a>.</dd>
<dt><a id="gloss:indexing"><strong>indexing</strong></a></dt>
<dd class="defbody">
<a id="idx:indexing:2107"></a>Indexing is a technique used to quickly 
select candidate <a class="gloss" href="glossary.html#gloss:clause">clauses</a> 
of a <a class="gloss" href="glossary.html#gloss:predicate">predicate</a> 
for a specific <a class="gloss" href="glossary.html#gloss:goal">goal</a>. 
In most Prolog systems, indexing is done (only) on the first <a class="gloss" href="glossary.html#gloss:argument">argument</a> 
of the <a class="gloss" href="glossary.html#gloss:head">head</a>. If 
this argument is instantiated to an <a class="gloss" href="glossary.html#gloss:atom">atom</a>, <a class="gloss" href="glossary.html#gloss:integer">integer</a>, <a class="gloss" href="glossary.html#gloss:float">float</a> 
or
<a class="gloss" href="glossary.html#gloss:compound">compound</a> term 
with <a class="gloss" href="glossary.html#gloss:functor">functor</a>, <a class="gloss" href="glossary.html#gloss:hashing">hashing</a> 
is used to quickly select all <a class="gloss" href="glossary.html#gloss:clause">clauses</a> 
where the first argument may <a class="gloss" href="glossary.html#gloss:unify">unify</a> 
with the first argument of the <a class="gloss" href="glossary.html#gloss:goal">goal</a>. 
SWI-Prolog supports just-in-time and multi-argument indexing. See <a class="sec" href="jitindex.html">section 
2.17</a>.</dd>
<dt><a id="gloss:integer"><strong>integer</strong></a></dt>
<dd class="defbody">
<a id="idx:integer:2108"></a>Whole number. On all implementations of 
SWI-Prolog integers are at least 64-bit signed values. When linked to 
the GNU GMP library, integer arithmetic is unbounded. See also <a id="idx:currentprologflag2:2109"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>, 
flags <a class="flag" href="flags.html#flag:bounded">bounded</a>, <a class="flag" href="flags.html#flag:max_integer">max_integer</a> 
and <a class="flag" href="flags.html#flag:min_integer">min_integer</a>.</dd>
<dt><a id="gloss:interpreted"><strong>interpreted</strong></a></dt>
<dd class="defbody">
<a id="idx:interpreted:2110"></a>As opposed to <a class="gloss" href="glossary.html#gloss:compile">compiled</a>, 
interpreted means the Prolog system attempts to prove a <a class="gloss" href="glossary.html#gloss:goal">goal</a> 
by directly reading the <a class="gloss" href="glossary.html#gloss:clause">clauses</a> 
rather than executing instructions from an (abstract) instruction set 
that is not or only indirectly related to Prolog.</dd>
<dt><a id="gloss:instantiation"><strong>instantiation [of an argument]</strong></a></dt>
<dd class="defbody">
<a id="idx:instantiation:2111"></a>To what extend a term is bound to a 
value. Typical levels are `unbound' (a <a class="gloss" href="glossary.html#gloss:variable">variable</a>), 
`ground' (term without variables) or `partially bound' (term with 
embedded variables).</dd>
<dt><a id="gloss:meta-predicate"><strong>meta-predicate</strong></a></dt>
<dd class="defbody">
<a id="idx:metapredicate:2112"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a> 
that reasons about other <a class="gloss" href="glossary.html#gloss:predicate">predicates</a>, 
either by calling them, (re)defining them or querying <a class="gloss" href="glossary.html#gloss:property">properties</a>.</dd>
<dt><a id="gloss:mode"><strong>mode [declaration]</strong></a></dt>
<dd class="defbody">
<a id="idx:mode:2113"></a>Declaration of an argument <a class="gloss" href="glossary.html#gloss:instantiation">instantiation</a> 
pattern for a
<a class="gloss" href="glossary.html#gloss:predicate">predicate</a>, 
often accompanied with a <a class="gloss" href="glossary.html#gloss:determinism">determinism</a>.</dd>
<dt><a id="gloss:module"><strong>module</strong></a></dt>
<dd class="defbody">
<a id="idx:module:2114"></a>Collection of predicates. Each module 
defines a name-space for predicates. <a class="gloss" href="glossary.html#gloss:built-in">built-in</a> 
predicates are accessible from all modules. Predicates can be published 
(<a class="gloss" href="glossary.html#gloss:exported">exported</a>) and <a class="gloss" href="glossary.html#gloss:imported">imported</a> 
to make their definition available to other modules.</dd>
<dt><a id="gloss:module-transparent"><strong>module transparent [predicate]</strong></a></dt>
<dd class="defbody">
<a id="idx:moduletransparent:2115"></a><a id="idx:transparent:2116"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a> 
that does not change the <a class="gloss" href="glossary.html#gloss:context-module">context module</a>. 
Sometimes also called a <a class="gloss" href="glossary.html#gloss:meta-predicate">meta-predicate</a>.</dd>
<dt><a id="gloss:multi"><strong>multi [determinism]</strong></a></dt>
<dd class="defbody">
<a id="idx:multi:2117"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a> 
is said to have <a class="gloss" href="glossary.html#gloss:determinism">determinism</a> 
multi if it generates at
<em>least</em> one answer.</dd>
<dt><a id="gloss:multifile"><strong>multifile [predicate]</strong></a></dt>
<dd class="defbody">
Predicate for which the definition is distributed over multiple source 
files. See <a id="idx:multifile1:2118"></a><a class="pred" href="dynamic.html#multifile/1">multifile/1</a>.</dd>
<dt><a id="gloss:neck"><strong>neck</strong></a></dt>
<dd class="defbody">
<a id="idx:neck:2119"></a>Operator (<code><code>:-</code></code>) 
separating <a class="gloss" href="glossary.html#gloss:head">head</a> 
from <a class="gloss" href="glossary.html#gloss:body">body</a> in a <a class="gloss" href="glossary.html#gloss:clause">clause</a>.</dd>
<dt><a id="gloss:nondet"><strong>nondet</strong></a></dt>
<dd class="defbody">
<a id="idx:nondet:2120"></a>Short for <a class="gloss" href="glossary.html#gloss:non-deterministic">non deterministic</a>.</dd>
<dt><a id="gloss:non-deterministic"><strong>non deterministic</strong></a></dt>
<dd class="defbody">
<a id="idx:nondeterministic:2121"></a>A <a class="gloss" href="glossary.html#gloss:non-deterministic">non deterministic</a> 
predicate is a predicate that mail fail or succeed any number of times.</dd>
<dt><a id="gloss:operator"><strong>operator</strong></a></dt>
<dd class="defbody">
<a id="idx:operator:2122"></a>Symbol (<a class="gloss" href="glossary.html#gloss:atom">atom</a>) 
that may be placed before its <a class="gloss" href="glossary.html#gloss:operand">operand</a> 
(prefix), after its <a class="gloss" href="glossary.html#gloss:operand">operand</a> 
(postfix) or between its two <a class="gloss" href="glossary.html#gloss:operand">operands</a> 
(infix).

<p>In Prolog, the expression <code>a+b</code> is exactly the same as the 
canonical term <code>+(a,b)</code>.</dd>
<dt><a id="gloss:operand"><strong>operand</strong></a></dt>
<dd class="defbody">
<a id="idx:operand:2123"></a><a class="gloss" href="glossary.html#gloss:argument">Argument</a> 
of an <a class="gloss" href="glossary.html#gloss:operator">operator</a>.</dd>
<dt><a id="gloss:precedence"><strong>precedence</strong></a></dt>
<dd class="defbody">
<a id="idx:precedence:2124"></a>The <a class="gloss" href="glossary.html#gloss:priority">priority</a> 
of an <a class="gloss" href="glossary.html#gloss:operator">operator</a>. 
Operator precedence is used to interpret <code>a+b*c</code> as <code>+(a, *(b,c))</code>.</dd>
<dt><a id="gloss:predicate"><strong>predicate</strong></a></dt>
<dd class="defbody">
<a id="idx:predicate:2125"></a>Collection of <a class="gloss" href="glossary.html#gloss:clause">clauses</a> 
with the same <a class="gloss" href="glossary.html#gloss:functor">functor</a> 
(name/<a class="gloss" href="glossary.html#gloss:arity">arity</a>). If a <a class="gloss" href="glossary.html#gloss:goal">goal</a> 
is proved, the system looks for a <a class="gloss" href="glossary.html#gloss:predicate">predicate</a> 
with the same functor, then uses <a class="gloss" href="glossary.html#gloss:indexing">indexing</a> 
to select candidate <a class="gloss" href="glossary.html#gloss:clause">clauses</a> 
and then tries these <a class="gloss" href="glossary.html#gloss:clause">clauses</a> 
one-by-one. See also <a class="gloss" href="glossary.html#gloss:backtracking">backtracking</a>.</dd>
<dt><a id="gloss:predicate-indicator"><strong>predicate indicator</strong></a></dt>
<dd class="defbody">
<a id="idx:predicateindicator:2126"></a>Term of the form Name/Arity 
(traditional) or Name//Arity (ISO DCG proposal), where Name is an atom 
and Arity a non-negative integer. It acts as an <em>indicator</em> (or 
reference) to a predicate or
<b>DCG</b> rule.</dd>
<dt><a id="gloss:priority"><strong>priority</strong></a></dt>
<dd class="defbody">
<a id="idx:priority:2127"></a>In the context of <a class="gloss" href="glossary.html#gloss:operator">operators</a> 
a synonym for <a class="gloss" href="glossary.html#gloss:precedence">precedence</a>.</dd>
<dt><a id="gloss:program"><strong>program</strong></a></dt>
<dd class="defbody">
<a id="idx:program:2128"></a>Collection of <a class="gloss" href="glossary.html#gloss:predicate">predicates</a>.</dd>
<dt><a id="gloss:property"><strong>property</strong></a></dt>
<dd class="defbody">
<a id="idx:property:2129"></a>Attribute of an object. SWI-Prolog defines 
various <em>*_property</em> predicates to query the status of 
predicates, clauses. etc.</dd>
<dt><a id="gloss:prove"><strong>prove</strong></a></dt>
<dd class="defbody">
<a id="idx:prove:2130"></a>Process where Prolog attempts to prove a <a class="gloss" href="glossary.html#gloss:query">query</a> 
using the available
<a class="gloss" href="glossary.html#gloss:predicate">predicates</a>.</dd>
<dt><a id="gloss:public-list"><strong>public list</strong></a></dt>
<dd class="defbody">
<a id="idx:publiclist:2131"></a>List of <a class="gloss" href="glossary.html#gloss:predicate">predicates</a> 
exported from a <a class="gloss" href="glossary.html#gloss:module">module</a>.</dd>
<dt><a id="gloss:query"><strong>query</strong></a></dt>
<dd class="defbody">
See <a class="gloss" href="glossary.html#gloss:goal">goal</a>.</dd>
<dt><a id="gloss:retract"><strong>retract</strong></a></dt>
<dd class="defbody">
<a id="idx:retract:2132"></a>Remove a <a class="gloss" href="glossary.html#gloss:clause">clause</a> 
from a <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>. 
See also <a class="gloss" href="glossary.html#gloss:dynamic">dynamic</a>,
<a class="gloss" href="glossary.html#gloss:update-view">update view</a> 
and <a class="gloss" href="glossary.html#gloss:assert">assert</a>.</dd>
<dt><a id="gloss:semidet"><strong>semidet</strong></a></dt>
<dd class="defbody">
<a id="idx:semidet:2133"></a>Shorthand for </dd>
<dt><a id="gloss:semi-deterministic"><strong>semi deterministic</strong></a></dt>
<dd class="defbody">
.</dd>
<dt><a id="gloss:semi-deterministic"><strong>semi deterministic</strong></a></dt>
<dd class="defbody">
<a id="idx:semideterministic:2134"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a> 
that is <a class="gloss" href="glossary.html#gloss:semi-deterministic">semi deterministic</a> 
either fails or succeeds exactly once without a <a class="gloss" href="glossary.html#gloss:choice-point">choice point</a>. 
See also
<a class="gloss" href="glossary.html#gloss:deterministic">deterministic</a>.</dd>
<dt><a id="gloss:shared"><strong>shared</strong></a></dt>
<dd class="defbody">
<a id="idx:shared:2135"></a>Two <a class="gloss" href="glossary.html#gloss:variable">variables</a> 
are called <a class="gloss" href="glossary.html#gloss:shared">shared</a> 
after they are <a class="gloss" href="glossary.html#gloss:unify">unified</a>. 
This implies if either of them is <a class="gloss" href="glossary.html#gloss:binding">bound</a>, 
the other is bound to the same value:

<pre class="code">
?- A = B, A = a.
A = B, B = a.
</pre>

</dd>
<dt><a id="gloss:singleton"><strong>singleton [variable]</strong></a></dt>
<dd class="defbody">
<a id="idx:singleton:2136"></a><a class="gloss" href="glossary.html#gloss:variable">Variable</a> 
appearing only one time in a <a class="gloss" href="glossary.html#gloss:clause">clause</a>. 
SWI-Prolog normally warns for this to avoid you making spelling 
mistakes. If a variable appears on purpose only once in a clause, write 
it as <code>_</code> (see <a class="gloss" href="glossary.html#gloss:anonymou">anonymous</a>). 
Rules for naming a variable and avoiding a warning are given in <a class="sec" href="syntax.html">section 
2.15.2.5</a>.</dd>
<dt><a id="gloss:solution"><strong>solution</strong></a></dt>
<dd class="defbody">
<a id="idx:solution:2137"></a><a class="gloss" href="glossary.html#gloss:binding">Bindings</a> 
resulting from a successfully <a class="gloss" href="glossary.html#gloss:prove">prove</a>n <a class="gloss" href="glossary.html#gloss:goal">goal</a>.</dd>
<dt><a id="gloss:structure"><strong>structure</strong></a></dt>
<dd class="defbody">
<a id="idx:structure:2138"></a>Synonym for <a class="gloss" href="glossary.html#gloss:compound">compound</a> 
term.</dd>
<dt><a id="gloss:string"><strong>string</strong></a></dt>
<dd class="defbody">
Used for the following representations of text: a packed array (see <a class="sec" href="strings.html">section 
5.2</a>, SWI-Prolog specific), a list of character codes or a list of 
one-character <a class="gloss" href="glossary.html#gloss:atom">atoms</a>.</dd>
<dt><a id="gloss:succeed"><strong>succeed</strong></a></dt>
<dd class="defbody">
<a id="idx:succeed:2139"></a>A <a class="gloss" href="glossary.html#gloss:goal">goal</a> 
is said to have <a class="gloss" href="glossary.html#gloss:succeed">succeeded</a> 
if it has been <a class="gloss" href="glossary.html#gloss:prove">proven</a>.</dd>
<dt><a id="gloss:term"><strong>term</strong></a></dt>
<dd class="defbody">
<a id="idx:term:2140"></a>Value in Prolog. A <a class="gloss" href="glossary.html#gloss:term">term</a> 
is either a <a class="gloss" href="glossary.html#gloss:variable">variable</a>, <a class="gloss" href="glossary.html#gloss:atom">atom</a>, <a class="gloss" href="glossary.html#gloss:integer">integer</a>,
<a class="gloss" href="glossary.html#gloss:float">float</a> or <a class="gloss" href="glossary.html#gloss:compound">compound</a> 
term. In addition, SWI-Prolog also defines the type <a class="gloss" href="glossary.html#gloss:string">string</a>.</dd>
<dt><a id="gloss:transparent"><strong>transparent</strong></a></dt>
<dd class="defbody">
See <a class="gloss" href="glossary.html#gloss:module-transparent">module transparent</a>.</dd>
<dt><a id="gloss:unify"><strong>unify</strong></a></dt>
<dd class="defbody">
<a id="idx:unify:2141"></a>Prolog process to make two terms equal by 
assigning variables in one term to values at the corresponding location 
of the other term. For example:

<pre class="code">
?- foo(a, B) = foo(A, b).
A = a,
B = b.
</pre>

<p>Unlike assignment (which does not exist in Prolog), unification is 
not directed.</dd>
<dt><a id="gloss:update-view"><strong>update view</strong></a></dt>
<dd class="defbody">
<a id="idx:updateview:2142"></a><a id="idx:viewupdate:2143"></a>How 
Prolog behaves when a <a class="gloss" href="glossary.html#gloss:dynamic">dynamic</a> <a class="gloss" href="glossary.html#gloss:predicate">predicate</a> 
is changed while it is running. There are two models. In most older 
Prolog systems the change becomes immediately visible to the <a class="gloss" href="glossary.html#gloss:goal">goal</a>, 
in modern systems including SWI-Prolog, the running <a class="gloss" href="glossary.html#gloss:goal">goal</a> 
is not affected. Only new <a class="gloss" href="glossary.html#gloss:goal">goals</a> 
`see' the new definition.</dd>
<dt><a id="gloss:variable"><strong>variable</strong></a></dt>
<dd class="defbody">
<a id="idx:variable:2144"></a>A Prolog variable is a value that `is not 
yet bound'. After <a class="gloss" href="glossary.html#gloss:binding">binding</a> 
a variable, it cannot be modified. <a class="gloss" href="glossary.html#gloss:backtracking">Backtracking</a> 
to a point in the execution before the variable was bound will turn it 
back into a variable:

<pre class="code">
?- A = b, A = c.
false.

?- (A = b; true; A = c).
A = b ;
true ;
A = c .
</pre>

<p>See also <a class="gloss" href="glossary.html#gloss:unify">unify</a>.

<p></dd>
</dl>

</body></html>
swi-prolog-nox 7.2.3-2 / usr / lib / swi-prolog / doc / Manual / glossary.html
