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<h1><a href="start.html" accesskey="h" title="[H]"><img src="lib/tpl/dokuwiki/images/logo.png" width="64" height="64" alt="" /> <span>BASIC 256 - Language Documentation</span></a></h1>
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<h3 class="toggle">Table of Contents</h3>
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<li class="level2"><div class="li"><a href="el_techinformation.html#developer_and_technical">Developer and Technical</a></div>
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<li class="level3"><div class="li"><a href="el_techinformation.html#overview">Overview</a></div></li>
<li class="level3"><div class="li"><a href="el_techinformation.html#to_do">To do</a></div></li>
<li class="level3"><div class="li"><a href="el_techinformation.html#the_life_of_a_basic-256_program">The life of a BASIC-256 program</a></div></li>
<li class="level3"><div class="li"><a href="el_techinformation.html#graphical_output">Graphical Output</a></div></li>
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<h2 class="sectionedit1" id="developer_and_technical">Developer and Technical</h2>
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<h3 class="sectionedit2" id="overview">Overview</h3>
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<p>
BASIC-256 programs are first compiled to byte code using LEX and YACC, and then run by interpreting the byte code in a stack machine. Adding functions is a simple matter of adding a byte code, letting LEX and YACC know how to parse the syntax, and coding the appropriate instruction in the interpreter. If you've never written a compiler or interpreter, the BASIC-256 internals would provide an excellent introduction to the basics of that.
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<p>
Please keep in mind that BASIC-256 is a teaching language for children (target ages 7-9), so we'd like to stay away from advanced concepts as much as possible. While it would be fun to make BASIC-256 a powerful high-level language, there are already much better languages that exist to fill that need: Python, Scheme.
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<h3 class="sectionedit3" id="to_do">To do</h3>
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<li class="level1"><div class="li"> Real-time error checking in the editor (parse each line just after it's typed)</div>
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<h3 class="sectionedit4" id="the_life_of_a_basic-256_program">The life of a BASIC-256 program</h3>
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<li class="level1"><div class="li"> BASIC program parsed into tokens by LEX</div>
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<li class="level1"><div class="li"> LEX feeds tokens to YACC</div>
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<li class="level1"><div class="li"> YACC determines if line is valid syntax. If so, it adds the appropriate byte codes to the byte-coded program</div>
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<li class="level1"><div class="li"> If no syntax errors occur, the C++ portion of the program interprets the byte code one instruction at a time, using a stack machine</div>
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<li class="level1"><div class="li"> Run time errors halt program execution and display an error message on the screen</div>
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<h3 class="sectionedit5" id="graphical_output">Graphical Output</h3>
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<p>
All graphing functions are performed on a buffer, which is subsequently written to the screen immediately after each operation. This is intentionally inefficient. The “fast” way to do this would be to have a separate rendering thread that calls a display routine when it's done, or to do all the rendering in the display routine.
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<p>
This is an ideal illustration of concessions made in BASIC-256 to keep things simple. We're interested in kids being able to see their dots move across the screen without having to explain double-buffering and multi-threading. We also want to allow them to write games like Pong that test for collisions using basic geometric formulas and draw the ball and paddles in a single loop. The current approach allows for this.
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<p>
Note: To speed things up for children doing more advanced programs, the <a href="el_fastgraphics.html" class="wikilink1" title="el:fastgraphics">FASTGRAPHICS</a> mode has been added. When in this mode, the display will only be updated when the BASIC program uses the <a href="el_refresh.html" class="wikilink1" title="el:refresh">REFRESH</a> command. This allows kids to benefit from double-buffering without having to understand it completely.
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<div class="docInfo"><bdi>el/techinformation.txt</bdi> · Last modified: 2014/01/11 23:26 (external edit)</div>
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