Changeset 4336

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Timestamp:
07/01/08 09:53:49 (2 months ago)
Author:
pmoura
Message:

Improved the Prolog migration guide on converting code that makes use of multifile predicates.

Location:
trunk
Files:
3 modified

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  • trunk/manuals/index.html

    r4323 r4336  
    3232    <div class="copyright"> 
    3333        <span>Copyright &copy; <a href="mailto:pmoura@logtalk.org">Paulo Moura</a> &mdash; <a href="http://logtalk.org">Logtalk.org</a></span><br/>  
    34         <span>Last updated on: May 30, 2008</span> 
     34        <span>Last updated on: July 1, 2008</span> 
    3535    </div> 
    3636    <div class="navbottom"> 

  • trunk/manuals/migration/index.html

    r3847 r4336  
    5656By adding the <em>gateway</em> clause after or before the local clauses, you can choose if the local clauses should be used before or after the overridden clauses. 
    5757</p> 
     58<p> 
     59A more complicated scenario is when you have several files containing clauses for a multifile predicate. For example, assume that a multifile predicate named <code>mp/2</code> is defined in two files. In this case, start by defining a protocol containing the declaration of the multifile predicate: 
     60</p> 
     61<pre> 
     62:- protocol(ptc).  
     63 
     64    :- public(mp/1).  
     65 
     66:- end_protocol.  
     67</pre> 
     68<p> 
     69Second, for each file, define a category containing the corresponding clauses for the <code>mp/2</code> predicate:  
     70</p> 
     71<pre> 
     72:- category(ctg1,  
     73    implements(ptc)).  
     74 
     75    mp(1).    % clauses from the first file 
     76    mp(2).  
     77 
     78:- end_category.  
     79 
     80 
     81:- category(ctg2,  
     82    implements(ptc)). 
     83 
     84    mp(3).    % clauses from the first file 
     85    mp(4).  
     86 
     87:- end_category.  
     88</pre> 
     89<p> 
     90Next, define an object importing all the categories and defining aliases to the imported predicates: 
     91</p> 
     92<pre> 
     93:- object(obj,  
     94    implements(ptc),  
     95    imports(ctg1, ctg2)). 
     96 
     97    :- alias(ctg1, mp/1, ctg1_mp/1).  
     98    :- alias(ctg2, mp/1, ctg2_mp/1).  
     99 
     100    mp(X) :-  
     101        ::ctg1_mp(X).  
     102    mp(X) :-  
     103        ::ctg2_mp(X).  
     104 
     105:- end_ object.  
     106</pre> 
     107<p> 
     108The predicate aliases above are needed to allow access to the overridded clauses of the <code>mp/1</code> predicate (by default, the clauses from  <code>ctg1</code> would override the clauses from the <code>ctg2</code> category as a consequence of the predicate lookup mechanism).  
     109</p> 
     110<p> 
     111Compiling and loading the above Logtalk entities allows you to access all clauses of the former multifile predicate. For example:  
     112</p> 
     113<pre> 
     114| ?- obj::mp(X). 
     115 
     116X = 1 ;  
     117X = 2 ;  
     118X = 3 ;  
     119X = 4  
     120yes  
     121</pre> 
    58122 
    59123<h2>Converting Prolog modules into objects<a id="converting"></a></h2> 
    … …  
    143207    <div class="copyright"> 
    144208        <span>Copyright &copy; <a href="mailto:pmoura@logtalk.org">Paulo Moura</a> &mdash; <a href="http://logtalk.org">Logtalk.org</a></span><br/>  
    145         <span>Last updated on: June 6, 2007</span> 
     209        <span>Last updated on: July 1, 2008</span> 
    146210    </div> 
    147211    <div class="navbottom"> 

  • trunk/RELEASE_NOTES.txt

    r4331 r4336  
    4949    "sicstus3.config" to avoid being mistaken for the SICStus Prolog 4  
    5050    config file. 
     51 
     52    Improved the Prolog migration guide on converting code that makes use  
     53    of multifile predicates. 
    5154 
    5255    Updated the support for the Pygments syntax highlighter to avoid marking