<!DOCTYPE html> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <meta name="generator" content="hevea 2.05"> <meta name="Author" content="Daniel Diaz"> <meta name="Keywords" content="GNU Prolog, manual, Prolog, compiler, constraints, finite domains"> <link rel="icon" type="image/x-icon" href="/gprolog.ico"><link rel="stylesheet" type="text/css" href="gprolog.css"> <title>Prolog directives</title> </head> <body TEXT=black BGCOLOR=white> <a href="gprolog021.html"><img src="contents_motif.gif" alt="Up"></a> <a href="gprolog023.html"><img src="next_motif.gif" alt="Next"></a> <hr> <h3 class="subsection" id="sec49">7.1  Prolog directives</h3> <ul> <li><a href="gprolog022.html#sec50">Introduction</a> </li><li><a href="gprolog022.html#dynamic%2F1"><span class="c003">dynamic/1</span> </a> </li><li><a href="gprolog022.html#public%2F1"><span class="c003">public/1</span> </a> </li><li><a href="gprolog022.html#sec53"><span class="c003">multifile/1</span></a> </li><li><a href="gprolog022.html#sec54"><span class="c003">discontiguous/1</span></a> </li><li><a href="gprolog022.html#sec55"><span class="c003">ensure_linked/1</span></a> </li><li><a href="gprolog022.html#sec56"><span class="c003">built_in/0</span>, <span class="c003">built_in/1</span>, <span class="c003">built_in_fd/0</span>, <span class="c003">built_in_fd/1</span></a> </li><li><a href="gprolog022.html#sec57"><span class="c003">include/1</span></a> </li><li><a href="gprolog022.html#sec58"><span class="c003">if/1</span>, <span class="c003">else/0</span>, <span class="c003">endif/0</span>, <span class="c003">elif/1</span> </a> </li><li><a href="gprolog022.html#sec59"><span class="c003">ensure_loaded/1</span></a> </li><li><a href="gprolog022.html#op%2F3"><span class="c003">op/3</span> </a> </li><li><a href="gprolog022.html#sec61"><span class="c003">char_conversion/2</span></a> </li><li><a href="gprolog022.html#sec62"><span class="c003">set_prolog_flag/2</span></a> </li><li><a href="gprolog022.html#initialization%2F1"><span class="c003">initialization/1</span> </a> </li><li><a href="gprolog022.html#foreign%2F2"><span class="c003">foreign/2</span>, <span class="c003">foreign/1</span> </a> </li></ul> <h4 class="subsubsection" id="sec50">7.1.1  Introduction</h4> <p> Prolog directives are annotations inserted in Prolog source files for the compiler. A Prolog directive is used to specify:</p><ul class="itemize"><li class="li-itemize">the properties of some procedures defined in the source file.</li><li class="li-itemize">the format and the syntax for read-terms in the source file (using changeable Prolog flags).</li><li class="li-itemize">included source files.</li><li class="li-itemize">a goal to be executed at run-time.</li></ul> <h4 class="subsubsection" id="dynamic/1">7.1.2  <a id="hevea_default183"></a><span class="c003">dynamic/1</span> </h4> <p><span class="c009">Templates</span></p><dl class="list"><dt class="dt-list"> </dt><dd class="dd-list"><span class="c003"> dynamic(+predicate_indicator)<br> dynamic(+predicate_indicator_list)<br> dynamic(+predicate_indicator_sequence)</span></dd></dl><p><span class="c009">Description</span></p><p><span class="c003">dynamic(Pred)</span> specifies that the procedure whose predicate indicator is <span class="c003">Pred</span> is a dynamic procedure. This directive makes it possible to alter the definition of <span class="c003">Pred</span> by adding or removing clauses. For more information refer to the section about dynamic clause management (section <a href="gprolog031.html#Introduction%3A%28Dynamic-clause-management%29">8.7.1</a>).</p><p>This directive shall precede the definition of <span class="c003">Pred</span> in the source file.</p><p>If there is no clause for <span class="c003">Pred</span> in the source file, <span class="c003">Pred</span> exists however as an empty predicate (this means that <span class="c003">current_predicate(Pred)</span> succeeds).</p><p>In order to allow multiple definitions, <span class="c003">Pred</span> can also be a list of predicate indicators or a sequence of predicate indicators using <span class="c003">’,’/2</span> as separator.</p><p><span class="c009">Portability</span></p><p>ISO directive.</p> <h4 class="subsubsection" id="public/1">7.1.3  <a id="hevea_default184"></a><span class="c003">public/1</span> </h4> <p><span class="c009">Templates</span></p><dl class="list"><dt class="dt-list"> </dt><dd class="dd-list"><span class="c003"> public(+predicate_indicator)<br> public(+predicate_indicator_list)<br> public(+predicate_indicator_sequence)</span></dd></dl><p><span class="c009">Description</span></p><p><span class="c003">public(Pred)</span> specifies that the procedure whose predicate indicator is <span class="c003">Pred</span> is a public procedure. This directive makes it possible to inspect the clauses of <span class="c003">Pred</span>. For more information refer to the section about dynamic clause management (section <a href="gprolog031.html#Introduction%3A%28Dynamic-clause-management%29">8.7.1</a>).</p><p>This directive shall precede the definition of <span class="c003">Pred</span> in the source file. Since a dynamic procedure is also public. It is useless (but correct) to define a public directive for a predicate already declared as dynamic.</p><p>In order to allow multiple definitions, <span class="c003">Pred</span> can also be a list of predicate indicators or a sequence of predicate indicators using <span class="c003">’,’/2</span> as separator.</p><p><span class="c009">Portability</span></p><p>GNU Prolog directive. The ISO reference does not define any directive to declare a predicate public but it does distinguish public predicates. It is worth noting that in most Prolog systems the <span class="c003">public/1</span> directive is as a visibility declaration. Indeed, declaring a predicate as public makes it visible from any predicate defined in any other file (otherwise the predicate is only visible from predicates defined in the same source file as itself). When a module system is incorporated in GNU Prolog a more general visibility declaration shall be provided conforming to the ISO reference.</p> <h4 class="subsubsection" id="sec53">7.1.4  <a id="hevea_default185"></a><span class="c003">multifile/1</span></h4> <p><span class="c009">Templates</span></p><dl class="list"><dt class="dt-list"> </dt><dd class="dd-list"><span class="c003"> multifile(+predicate_indicator)<br> multifile(+predicate_indicator_list)<br> multifile(+predicate_indicator_sequence)</span></dd></dl><p><span class="c009">Description</span></p><p><span class="c003">multifile(Pred)</span> specifies that the procedure whose predicate indicator is <span class="c003">Pred</span> is a multifle procedure (the clauses of <span class="c003">Pred</span> can reside in several source files). This directive is only supported by GNU Prolog since version 1.4.0.</p><p><span class="c009">Portability</span></p><p>ISO directive.</p> <h4 class="subsubsection" id="sec54">7.1.5  <a id="hevea_default186"></a><span class="c003">discontiguous/1</span></h4> <p><span class="c009">Templates</span></p><dl class="list"><dt class="dt-list"> </dt><dd class="dd-list"><span class="c003"> discontiguous(+predicate_indicator)<br> discontiguous(+predicate_indicator_list)<br> discontiguous(+predicate_indicator_sequence)</span></dd></dl><p><span class="c009">Description</span></p><p><span class="c003">discontiguous(Pred)</span> specifies that the procedure whose predicate indicator is <span class="c003">Pred</span> is a discontiguous procedure. Namely, the clauses defining <span class="c003">Pred</span> are not restricted to be consecutive but can appear anywhere in the source file.</p><p>This directive shall precede the definition of <span class="c003">Pred</span> in the source file.</p><p>In order to allow multiple definitions, <span class="c003">Pred</span> can also be a list of predicate indicators or a sequence of predicate indicators using <span class="c003">’,’/2</span> as separator.</p><p>A multifile predicate cannot be directly called from a file where it is not declared as multifile (the native compiler must know the called predicate is multifile). Workarounds: either call it via a meta-call (e.g. using <span class="c003">call/1</span>) or declare it as multifile in the calling source file). A good habit is to encapsulate a multifile predicate in a monofile predicate which invokes it (external call only invoke the monofile wrapper predicate).</p><p><span class="c009">Portability</span></p><p>ISO directive. </p> <h4 class="subsubsection" id="sec55">7.1.6  <a id="hevea_default187"></a><span class="c003">ensure_linked/1</span></h4> <p><span class="c009">Templates</span></p><dl class="list"><dt class="dt-list"> </dt><dd class="dd-list"><span class="c003"> ensure_linked(+predicate_indicator)<br> ensure_linked(+predicate_indicator_list)<br> ensure_linked(+predicate_indicator_sequence)</span></dd></dl><p><span class="c009">Description</span></p><p><span class="c003">ensure_linked(Pred)</span> specifies that the procedure whose predicate indicator is <span class="c003">Pred</span> must be included by the linker. This directive is useful when compiling to native code to force the linker to include the code of a given predicate. Indeed, if the <span class="c003">gplc</span> is invoked with an option to reduce the size of the executable (section <a href="gprolog009.html#Using-the-compiler">4.4.3</a>), the linker only includes the code of predicates that are statically referenced. However, the linker cannot detect dynamically referenced predicates (used as data passed to a meta-call predicate). The use of this directive prevents it to exclude the code of such predicates.</p><p>In order to allow multiple definitions, <span class="c003">Pred</span> can also be a list of predicate indicators or a sequence of predicate indicators using <span class="c003">’,’/2</span> as separator.</p><p><span class="c009">Portability</span></p><p>GNU Prolog directive.</p> <h4 class="subsubsection" id="sec56">7.1.7  <a id="hevea_default188"></a><span class="c003">built_in/0</span>, <a id="hevea_default189"></a><span class="c003">built_in/1</span>, <a id="hevea_default190"></a><span class="c003">built_in_fd/0</span>, <a id="hevea_default191"></a><span class="c003">built_in_fd/1</span></h4> <p><span class="c009">Templates</span></p><dl class="list"><dt class="dt-list"> </dt><dd class="dd-list"><span class="c003"> built_in<br> built_in(+predicate_indicator)<br> built_in(+predicate_indicator_list)<br> built_in(+predicate_indicator_sequence)<br> built_in_fd<br> built_in_fd(+predicate_indicator)<br> built_in_fd(+predicate_indicator_list)<br> built_in_fd(+predicate_indicator_sequence)</span></dd></dl><p><span class="c009">Description</span></p><p><span class="c003">built_in</span> specifies that the procedures defined from now have the <a id="hevea_default192"></a><span class="c003">built_in</span> property (section <a href="gprolog032.html#predicate-property%2F2">8.8.2</a>).</p><p><span class="c003">built_in(Pred)</span> is similar to <span class="c003">built_in/0</span> but only affects the procedure whose predicate indicator is <span class="c003">Pred</span>.</p><p>This directive shall precede the definition of <span class="c003">Pred</span> in the source file.</p><p>In order to allow multiple definitions, <span class="c003">Pred</span> can also be a list of predicate indicators or a sequence of predicate indicators using <span class="c003">’,’/2</span> as separator.</p><p><span class="c003">built_in_fd</span> (resp. <span class="c003">built_in_fd(Pred)</span>) is similar to <span class="c003">built_in</span> (resp. <span class="c003">built_in(Pred)</span>) but sets the <a id="hevea_default193"></a><span class="c003">built_in_fd</span> predicate property (section <a href="gprolog032.html#predicate-property%2F2">8.8.2</a>).</p><p><span class="c009">Portability</span></p><p>GNU Prolog directives.</p> <h4 class="subsubsection" id="sec57">7.1.8  <a id="hevea_default194"></a><span class="c003">include/1</span></h4> <p><span class="c009">Templates</span></p><dl class="list"><dt class="dt-list"> </dt><dd class="dd-list"><span class="c003"> include(+atom)</span></dd></dl><p><span class="c009">Description</span></p><p><span class="c003">include(File)</span> specifies that the content of the Prolog source <span class="c003">File</span> shall be inserted. The resulting Prolog text is identical to the Prolog text obtained by replacing the directive by the content of the Prolog source <span class="c003">File</span>.</p><p>In case of <span class="c003">File</span> is a relative file name, it is searched in the current directory. If it is not found it is then searched in each directory of parent includers.</p><p>See <a id="hevea_default195"></a><span class="c003">absolute_file_name/2</span> for information about the syntax of <span class="c003">File</span> (section <a href="gprolog050.html#absolute-file-name%2F2">8.26.1</a>).</p><p><span class="c009">Portability</span></p><p>ISO directive.</p> <h4 class="subsubsection" id="sec58">7.1.9  <a id="hevea_default196"></a><span class="c003">if/1</span>, <a id="hevea_default197"></a><span class="c003">else/0</span>, <a id="hevea_default198"></a><span class="c003">endif/0</span>, <a id="hevea_default199"></a><span class="c003">elif/1</span> </h4> <p><span class="c009">Templates</span></p><dl class="list"><dt class="dt-list"> </dt><dd class="dd-list"><span class="c003"> if(+callable_term) <br> else<br> endif<br> elif(+callable_term)</span></dd></dl><p><span class="c009">Description</span></p><p>These directives are for conditional compilation.</p><p><span class="c003">if(Goal)</span> compile subsequent code only if <span class="c003">Goal</span> succeeds. <span class="c003">Goal</span> is first processed by <span class="c003">expand_term/2</span> (section <a href="gprolog041.html#expand-term%2F2">8.17.2</a>). If <span class="c003">Goal</span> raises an exception it is printed and <span class="c003">Goal</span> fails.</p><p><span class="c003">else</span> introduces the <span class="c008">else</span> part.</p><p><span class="c003">endif</span> terminates a conditional compilation part.</p><p><span class="c003">elif(Goal)</span> is a shorthand for <span class="c003">:- else. :- if(Goal). </span>…<span class="c003"> :- endif</span>.</p><p><span class="c009">Portability</span></p><p>GNU Prolog directive. Also in SWI and YAP.</p> <h4 class="subsubsection" id="sec59">7.1.10  <a id="hevea_default200"></a><span class="c003">ensure_loaded/1</span></h4> <p><span class="c009">Templates</span></p><dl class="list"><dt class="dt-list"> </dt><dd class="dd-list"><span class="c003"> ensure_loaded(+atom)</span></dd></dl><p><span class="c009">Description</span></p><p><span class="c003">ensure_loaded(File)</span> is not supported by GNU Prolog. When such a directive is encountered it is simply ignored.</p><p><span class="c009">Portability</span></p><p>ISO directive. Not supported.</p> <h4 class="subsubsection" id="op/3">7.1.11  <a id="hevea_default201"></a><span class="c003">op/3</span> </h4> <p><span class="c009">Templates</span></p><dl class="list"><dt class="dt-list"> </dt><dd class="dd-list"><span class="c003"> op(+integer, +operator_specifier, +atom_or_atom_list)</span></dd></dl><p><span class="c009">Description</span></p><p><span class="c003">op(Priority, OpSpecifier, Operator)</span> alters the operator table. This directive is executed as soon as it is encountered by calling the built-in predicate <a id="hevea_default202"></a><span class="c003">op/3</span> (section <a href="gprolog038.html#op%2F3%3A%28Term-input%2Foutput%29">8.14.10</a>). A system directive is also generated to reflect the effect of this directive at run-time (section <a href="gprolog009.html#Running-an-executable">4.4.4</a>).</p><p><span class="c009">Portability</span></p><p>ISO directive.</p> <h4 class="subsubsection" id="sec61">7.1.12  <a id="hevea_default203"></a><span class="c003">char_conversion/2</span></h4> <p><span class="c009">Templates</span></p><dl class="list"><dt class="dt-list"> </dt><dd class="dd-list"><span class="c003"> char_conversion(+character, +character)</span></dd></dl><p><span class="c009">Description</span></p><p><span class="c003">char_conversion(InChar, OutChar)</span> alters the character-conversion mapping. This directive is executed as soon as it is encountered by a call to the built-in predicate <a id="hevea_default204"></a><span class="c003">char_conversion/2</span> (section <a href="gprolog038.html#char-conversion%2F2">8.14.12</a>). A system directive is also generated to reflect the effect of this directive at run-time (section <a href="gprolog009.html#Running-an-executable">4.4.4</a>).</p><p><span class="c009">Portability</span></p><p>ISO directive.</p> <h4 class="subsubsection" id="sec62">7.1.13  <a id="hevea_default205"></a><span class="c003">set_prolog_flag/2</span></h4> <p><span class="c009">Templates</span></p><dl class="list"><dt class="dt-list"> </dt><dd class="dd-list"><span class="c003"> set_prolog_flag(+flag, +term)</span></dd></dl><p><span class="c009">Description</span></p><p><span class="c003">set_prolog_flag(Flag, Value)</span> sets the value of the <a id="hevea_default206"></a>Prolog flag <span class="c003">Flag</span> to <span class="c003">Value</span>. This directive is executed as soon as it is encountered by a call to the built-in predicate <a id="hevea_default207"></a><span class="c003">set_prolog_flag/2</span> (section <a href="gprolog046.html#set-prolog-flag%2F2">8.22.1</a>). A system directive is also generated to reflect the effect of this directive at run-time (section <a href="gprolog009.html#Running-an-executable">4.4.4</a>).</p><p><span class="c009">Portability</span></p><p>ISO directive.</p> <h4 class="subsubsection" id="initialization/1">7.1.14  <a id="hevea_default208"></a><span class="c003">initialization/1</span> </h4> <p><span class="c009">Templates</span></p><dl class="list"><dt class="dt-list"> </dt><dd class="dd-list"><span class="c003"> initialization(+callable_term)</span></dd></dl><p><span class="c009">Description</span></p><p><span class="c003">initialization(Goal)</span> adds <span class="c003">Goal</span> to the set of goal which shall be executed at run-time. A user directive is generated to execute <span class="c003">Goal</span> at run-time. If several initialization directives appear in the same file they are executed in the order of appearance (section <a href="gprolog009.html#Running-an-executable">4.4.4</a>).</p><p><span class="c009">Portability</span></p><p>ISO directive.</p> <h4 class="subsubsection" id="foreign/2">7.1.15  <a id="hevea_default209"></a><span class="c003">foreign/2</span>, <a id="hevea_default210"></a><span class="c003">foreign/1</span> </h4> <p><span class="c009">Templates</span></p><dl class="list"><dt class="dt-list"> </dt><dd class="dd-list"><span class="c003"> foreign(+callable_term, +foreign_option_list)<br> foreign(+callable_term)</span></dd></dl><p><span class="c009">Description</span></p><p><span class="c003">foreign(Template, Options)</span> defines an interface predicate whose prototype is <span class="c003">Template</span> according to the options given by <span class="c003">Options</span>. Refer to the foreign code interface for more information (section <a href="gprolog068.html#Calling-C-from-Prolog">10.3</a>).</p><p><span class="c003">foreign(Template)</span> is equivalent to <span class="c003">foreign(Template, [])</span>.</p><p><span class="c009">Portability</span></p><p>GNU Prolog directive.</p> <hr class="c011"> Copyright (C) 1999-2013 Daniel Diaz Verbatim copying and distribution of this entire article is permitted in any medium, provided this notice is preserved. <a href="index.html#copyright">More about the copyright</a> <hr> <a href="gprolog021.html"><img src="contents_motif.gif" alt="Up"></a> <a href="gprolog023.html"><img src="next_motif.gif" alt="Next"></a> </body> </html>
