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POProlog - DCG parser with input from file
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  1. POProlog - DCG parser with input from file
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    copied!<p>As part of a project I need to write a parser that can read a file and parse into facts I can use in my program.</p> <p>The file structure looks as follows: </p> <pre><code>property = { el1 , el2 , ... }. </code></pre> <p>What I want in the end is:</p> <pre><code>property(el1). property(el2). ... </code></pre> <p>I read my file like this: </p> <pre><code>main :- open('myFile.txt', read, Str), read_file(Str,Lines), close(Str), write(Lines), nl. read_file(Stream,[]) :- at_end_of_stream(Stream). read_file(Stream,[X|L]) :- \+ at_end_of_stream(Stream), read(Stream,X), parse(X), % Here I call upon my parser. read_file(Stream,L). </code></pre> <p>Now I have read in several books and online about DCG, but they all explain the same simple examples where you can generate sentences like "the cat eats the bat" etc... When I want to use it for the above example I fail miserably.</p> <p>What I did manage was "parsing" the underneath line: </p> <pre><code>property = el1. </code></pre> <p>to </p> <pre><code>property(el1). </code></pre> <p>with this: </p> <pre><code>parse(X) :- X =.. List, % Reason I do this is because X is one atom and not a list. phrase(sentence(Statement), List), asserta(Statement). sentence(Statement) --&gt; ['=', Gender, Person] , { Statement =.. [Gender, Person] }. </code></pre> <p>I don't even know if I'm using the dcg in a correct way here, so any on help on this would be appreciated. Now the problem I having is, how to do this with multiple elements in my list, and how to handle '{' and '}'.<br> What I really want is a dcg that can handle these types of sentences (with more than 2 elements): <img src="https://i.stack.imgur.com/9ZstF.png" alt="Sentence split in parts"></p> <p>Now I know many people around here refer to the libraries dcg_basics and pio when it comes to dcgs. However, I have an additional problem that when I try to use the library I receive the error:</p> <pre><code>ERROR: (c:/users/ldevriendt/documents/prolog/file3.pl:3): Type error: `text' expected, found `http/dcg_basics' Warning: (c:/users/ldevriendt/documents/prolog/file3.pl:3): Goal (directive) failed: user:[library(http/dcg_basics)] </code></pre> <p>when I do this:</p> <pre><code>:- [library(http/dcg_basics)]. </code></pre> <p>Additional info:</p> <ul> <li>I use the program: <a href="http://lakk.bildung.hessen.de/netzwerk/faecher/informatik/swiprolog/indexe.html" rel="noreferrer">SWI-Prolog-Editor</a> on a Windows environment.</li> </ul> <p>Any help on this would be appreciated!</p> <p><strong>EDIT:</strong> The aim of this is question is to learn more about DCG and its use in parsers.</p>
 

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