1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316
|
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>1. Kaleidoscope: Kaleidoscope Introduction and the Lexer — LLVM 13 documentation</title>
<link rel="stylesheet" href="../../_static/pygments.css" type="text/css" />
<link rel="stylesheet" href="../../_static/llvm-theme.css" type="text/css" />
<script id="documentation_options" data-url_root="../../" src="../../_static/documentation_options.js"></script>
<script src="../../_static/jquery.js"></script>
<script src="../../_static/underscore.js"></script>
<script src="../../_static/doctools.js"></script>
<link rel="index" title="Index" href="../../genindex.html" />
<link rel="search" title="Search" href="../../search.html" />
<link rel="next" title="2. Kaleidoscope: Implementing a Parser and AST" href="LangImpl02.html" />
<link rel="prev" title="My First Language Frontend with LLVM Tutorial" href="index.html" />
<style type="text/css">
table.right { float: right; margin-left: 20px; }
table.right td { border: 1px solid #ccc; }
</style>
</head><body>
<div class="logo">
<a href="../../index.html">
<img src="../../_static/logo.png"
alt="LLVM Logo" width="250" height="88"/></a>
</div>
<div class="related" role="navigation" aria-label="related navigation">
<h3>Navigation</h3>
<ul>
<li class="right" style="margin-right: 10px">
<a href="../../genindex.html" title="General Index"
accesskey="I">index</a></li>
<li class="right" >
<a href="LangImpl02.html" title="2. Kaleidoscope: Implementing a Parser and AST"
accesskey="N">next</a> |</li>
<li class="right" >
<a href="index.html" title="My First Language Frontend with LLVM Tutorial"
accesskey="P">previous</a> |</li>
<li><a href="https://llvm.org/">LLVM Home</a> | </li>
<li><a href="../../index.html">Documentation</a>»</li>
<li class="nav-item nav-item-1"><a href="../../GettingStartedTutorials.html" >Getting Started/Tutorials</a> »</li>
<li class="nav-item nav-item-2"><a href="../index.html" >LLVM Tutorial: Table of Contents</a> »</li>
<li class="nav-item nav-item-3"><a href="index.html" accesskey="U">My First Language Frontend with LLVM Tutorial</a> »</li>
<li class="nav-item nav-item-this"><a href=""><span class="section-number">1. </span>Kaleidoscope: Kaleidoscope Introduction and the Lexer</a></li>
</ul>
</div>
<div class="sphinxsidebar" role="navigation" aria-label="main navigation">
<div class="sphinxsidebarwrapper">
<h3>Documentation</h3>
<ul class="want-points">
<li><a href="https://llvm.org/docs/GettingStartedTutorials.html">Getting Started/Tutorials</a></li>
<li><a href="https://llvm.org/docs/UserGuides.html">User Guides</a></li>
<li><a href="https://llvm.org/docs/Reference.html">Reference</a></li>
</ul>
<h3>Getting Involved</h3>
<ul class="want-points">
<li><a href="https://llvm.org/docs/Contributing.html">Contributing to LLVM</a></li>
<li><a href="https://llvm.org/docs/HowToSubmitABug.html">Submitting Bug Reports</a></li>
<li><a href="https://llvm.org/docs/GettingInvolved.html#mailing-lists">Mailing Lists</a></li>
<li><a href="https://llvm.org/docs/GettingInvolved.html#irc">IRC</a></li>
<li><a href="https://llvm.org/docs/GettingInvolved.html#meetups-and-social-events">Meetups and Social Events</a></li>
</ul>
<h3>Additional Links</h3>
<ul class="want-points">
<li><a href="https://llvm.org/docs/FAQ.html">FAQ</a></li>
<li><a href="https://llvm.org/docs/Lexicon.html">Glossary</a></li>
<li><a href="https://llvm.org/pubs">Publications</a></li>
<li><a href="https://github.com/llvm/llvm-project//">Github Repository</a></li>
</ul>
<div role="note" aria-label="source link">
<h3>This Page</h3>
<ul class="this-page-menu">
<li><a href="../../_sources/tutorial/MyFirstLanguageFrontend/LangImpl01.rst.txt"
rel="nofollow">Show Source</a></li>
</ul>
</div>
<div id="searchbox" style="display: none" role="search">
<h3 id="searchlabel">Quick search</h3>
<div class="searchformwrapper">
<form class="search" action="../../search.html" method="get">
<input type="text" name="q" aria-labelledby="searchlabel" />
<input type="submit" value="Go" />
</form>
</div>
</div>
<script>$('#searchbox').show(0);</script>
</div>
</div>
<div class="document">
<div class="documentwrapper">
<div class="bodywrapper">
<div class="body" role="main">
<div class="section" id="kaleidoscope-kaleidoscope-introduction-and-the-lexer">
<h1><span class="section-number">1. </span>Kaleidoscope: Kaleidoscope Introduction and the Lexer<a class="headerlink" href="#kaleidoscope-kaleidoscope-introduction-and-the-lexer" title="Permalink to this headline">¶</a></h1>
<div class="contents local topic" id="contents">
<ul class="simple">
<li><p><a class="reference internal" href="#the-kaleidoscope-language" id="id1">The Kaleidoscope Language</a></p></li>
<li><p><a class="reference internal" href="#the-lexer" id="id2">The Lexer</a></p></li>
</ul>
</div>
<div class="section" id="the-kaleidoscope-language">
<h2><a class="toc-backref" href="#id1"><span class="section-number">1.1. </span>The Kaleidoscope Language</a><a class="headerlink" href="#the-kaleidoscope-language" title="Permalink to this headline">¶</a></h2>
<p>This tutorial is illustrated with a toy language called
“<a class="reference external" href="http://en.wikipedia.org/wiki/Kaleidoscope">Kaleidoscope</a>” (derived
from “meaning beautiful, form, and view”). Kaleidoscope is a procedural
language that allows you to define functions, use conditionals, math,
etc. Over the course of the tutorial, we’ll extend Kaleidoscope to
support the if/then/else construct, a for loop, user defined operators,
JIT compilation with a simple command line interface, debug info, etc.</p>
<p>We want to keep things simple, so the only datatype in Kaleidoscope
is a 64-bit floating point type (aka ‘double’ in C parlance). As such,
all values are implicitly double precision and the language doesn’t
require type declarations. This gives the language a very nice and
simple syntax. For example, the following simple example computes
<a class="reference external" href="http://en.wikipedia.org/wiki/Fibonacci_number">Fibonacci numbers:</a></p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="c1"># Compute the x'th fibonacci number.</span>
<span class="k">def</span> <span class="nf">fib</span><span class="p">(</span><span class="n">x</span><span class="p">)</span>
<span class="k">if</span> <span class="n">x</span> <span class="o"><</span> <span class="mi">3</span> <span class="n">then</span>
<span class="mi">1</span>
<span class="k">else</span>
<span class="n">fib</span><span class="p">(</span><span class="n">x</span><span class="o">-</span><span class="mi">1</span><span class="p">)</span><span class="o">+</span><span class="n">fib</span><span class="p">(</span><span class="n">x</span><span class="o">-</span><span class="mi">2</span><span class="p">)</span>
<span class="c1"># This expression will compute the 40th number.</span>
<span class="n">fib</span><span class="p">(</span><span class="mi">40</span><span class="p">)</span>
</pre></div>
</div>
<p>We also allow Kaleidoscope to call into standard library functions - the
LLVM JIT makes this really easy. This means that you can use the
‘extern’ keyword to define a function before you use it (this is also
useful for mutually recursive functions). For example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">extern</span> <span class="n">sin</span><span class="p">(</span><span class="n">arg</span><span class="p">);</span>
<span class="n">extern</span> <span class="n">cos</span><span class="p">(</span><span class="n">arg</span><span class="p">);</span>
<span class="n">extern</span> <span class="n">atan2</span><span class="p">(</span><span class="n">arg1</span> <span class="n">arg2</span><span class="p">);</span>
<span class="n">atan2</span><span class="p">(</span><span class="n">sin</span><span class="p">(</span><span class="o">.</span><span class="mi">4</span><span class="p">),</span> <span class="n">cos</span><span class="p">(</span><span class="mi">42</span><span class="p">))</span>
</pre></div>
</div>
<p>A more interesting example is included in Chapter 6 where we write a
little Kaleidoscope application that <a class="reference external" href="LangImpl06.html#kicking-the-tires">displays a Mandelbrot
Set</a> at various levels of magnification.</p>
<p>Let’s dive into the implementation of this language!</p>
</div>
<div class="section" id="the-lexer">
<h2><a class="toc-backref" href="#id2"><span class="section-number">1.2. </span>The Lexer</a><a class="headerlink" href="#the-lexer" title="Permalink to this headline">¶</a></h2>
<p>When it comes to implementing a language, the first thing needed is the
ability to process a text file and recognize what it says. The
traditional way to do this is to use a
“<a class="reference external" href="http://en.wikipedia.org/wiki/Lexical_analysis">lexer</a>” (aka
‘scanner’) to break the input up into “tokens”. Each token returned by
the lexer includes a token code and potentially some metadata (e.g. the
numeric value of a number). First, we define the possibilities:</p>
<div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="c1">// The lexer returns tokens [0-255] if it is an unknown character, otherwise one</span>
<span class="c1">// of these for known things.</span>
<span class="k">enum</span> <span class="nc">Token</span> <span class="p">{</span>
<span class="n">tok_eof</span> <span class="o">=</span> <span class="mi">-1</span><span class="p">,</span>
<span class="c1">// commands</span>
<span class="n">tok_def</span> <span class="o">=</span> <span class="mi">-2</span><span class="p">,</span>
<span class="n">tok_extern</span> <span class="o">=</span> <span class="mi">-3</span><span class="p">,</span>
<span class="c1">// primary</span>
<span class="n">tok_identifier</span> <span class="o">=</span> <span class="mi">-4</span><span class="p">,</span>
<span class="n">tok_number</span> <span class="o">=</span> <span class="mi">-5</span><span class="p">,</span>
<span class="p">};</span>
<span class="k">static</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">IdentifierStr</span><span class="p">;</span> <span class="c1">// Filled in if tok_identifier</span>
<span class="k">static</span> <span class="kt">double</span> <span class="n">NumVal</span><span class="p">;</span> <span class="c1">// Filled in if tok_number</span>
</pre></div>
</div>
<p>Each token returned by our lexer will either be one of the Token enum
values or it will be an ‘unknown’ character like ‘+’, which is returned
as its ASCII value. If the current token is an identifier, the
<code class="docutils literal notranslate"><span class="pre">IdentifierStr</span></code> global variable holds the name of the identifier. If
the current token is a numeric literal (like 1.0), <code class="docutils literal notranslate"><span class="pre">NumVal</span></code> holds its
value. We use global variables for simplicity, but this is not the
best choice for a real language implementation :).</p>
<p>The actual implementation of the lexer is a single function named
<code class="docutils literal notranslate"><span class="pre">gettok</span></code>. The <code class="docutils literal notranslate"><span class="pre">gettok</span></code> function is called to return the next token
from standard input. Its definition starts as:</p>
<div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="c1">/// gettok - Return the next token from standard input.</span>
<span class="k">static</span> <span class="kt">int</span> <span class="n">gettok</span><span class="p">()</span> <span class="p">{</span>
<span class="k">static</span> <span class="kt">int</span> <span class="n">LastChar</span> <span class="o">=</span> <span class="sc">' '</span><span class="p">;</span>
<span class="c1">// Skip any whitespace.</span>
<span class="k">while</span> <span class="p">(</span><span class="n">isspace</span><span class="p">(</span><span class="n">LastChar</span><span class="p">))</span>
<span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
</pre></div>
</div>
<p><code class="docutils literal notranslate"><span class="pre">gettok</span></code> works by calling the C <code class="docutils literal notranslate"><span class="pre">getchar()</span></code> function to read
characters one at a time from standard input. It eats them as it
recognizes them and stores the last character read, but not processed,
in LastChar. The first thing that it has to do is ignore whitespace
between tokens. This is accomplished with the loop above.</p>
<p>The next thing <code class="docutils literal notranslate"><span class="pre">gettok</span></code> needs to do is recognize identifiers and
specific keywords like “def”. Kaleidoscope does this with this simple
loop:</p>
<div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="p">(</span><span class="n">isalpha</span><span class="p">(</span><span class="n">LastChar</span><span class="p">))</span> <span class="p">{</span> <span class="c1">// identifier: [a-zA-Z][a-zA-Z0-9]*</span>
<span class="n">IdentifierStr</span> <span class="o">=</span> <span class="n">LastChar</span><span class="p">;</span>
<span class="k">while</span> <span class="p">(</span><span class="n">isalnum</span><span class="p">((</span><span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">())))</span>
<span class="n">IdentifierStr</span> <span class="o">+=</span> <span class="n">LastChar</span><span class="p">;</span>
<span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"def"</span><span class="p">)</span>
<span class="k">return</span> <span class="n">tok_def</span><span class="p">;</span>
<span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"extern"</span><span class="p">)</span>
<span class="k">return</span> <span class="n">tok_extern</span><span class="p">;</span>
<span class="k">return</span> <span class="n">tok_identifier</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
</div>
<p>Note that this code sets the ‘<code class="docutils literal notranslate"><span class="pre">IdentifierStr</span></code>’ global whenever it
lexes an identifier. Also, since language keywords are matched by the
same loop, we handle them here inline. Numeric values are similar:</p>
<div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="p">(</span><span class="n">isdigit</span><span class="p">(</span><span class="n">LastChar</span><span class="p">)</span> <span class="o">||</span> <span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'.'</span><span class="p">)</span> <span class="p">{</span> <span class="c1">// Number: [0-9.]+</span>
<span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">NumStr</span><span class="p">;</span>
<span class="k">do</span> <span class="p">{</span>
<span class="n">NumStr</span> <span class="o">+=</span> <span class="n">LastChar</span><span class="p">;</span>
<span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
<span class="p">}</span> <span class="k">while</span> <span class="p">(</span><span class="n">isdigit</span><span class="p">(</span><span class="n">LastChar</span><span class="p">)</span> <span class="o">||</span> <span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'.'</span><span class="p">);</span>
<span class="n">NumVal</span> <span class="o">=</span> <span class="n">strtod</span><span class="p">(</span><span class="n">NumStr</span><span class="p">.</span><span class="n">c_str</span><span class="p">(),</span> <span class="mi">0</span><span class="p">);</span>
<span class="k">return</span> <span class="n">tok_number</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
</div>
<p>This is all pretty straightforward code for processing input. When
reading a numeric value from input, we use the C <code class="docutils literal notranslate"><span class="pre">strtod</span></code> function to
convert it to a numeric value that we store in <code class="docutils literal notranslate"><span class="pre">NumVal</span></code>. Note that
this isn’t doing sufficient error checking: it will incorrectly read
“1.23.45.67” and handle it as if you typed in “1.23”. Feel free to
extend it! Next we handle comments:</p>
<div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'#'</span><span class="p">)</span> <span class="p">{</span>
<span class="c1">// Comment until end of line.</span>
<span class="k">do</span>
<span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
<span class="k">while</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">!=</span> <span class="n">EOF</span> <span class="o">&&</span> <span class="n">LastChar</span> <span class="o">!=</span> <span class="sc">'\n'</span> <span class="o">&&</span> <span class="n">LastChar</span> <span class="o">!=</span> <span class="sc">'\r'</span><span class="p">);</span>
<span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">!=</span> <span class="n">EOF</span><span class="p">)</span>
<span class="k">return</span> <span class="n">gettok</span><span class="p">();</span>
<span class="p">}</span>
</pre></div>
</div>
<p>We handle comments by skipping to the end of the line and then return
the next token. Finally, if the input doesn’t match one of the above
cases, it is either an operator character like ‘+’ or the end of the
file. These are handled with this code:</p>
<div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span> <span class="c1">// Check for end of file. Don't eat the EOF.</span>
<span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">==</span> <span class="n">EOF</span><span class="p">)</span>
<span class="k">return</span> <span class="n">tok_eof</span><span class="p">;</span>
<span class="c1">// Otherwise, just return the character as its ascii value.</span>
<span class="kt">int</span> <span class="n">ThisChar</span> <span class="o">=</span> <span class="n">LastChar</span><span class="p">;</span>
<span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
<span class="k">return</span> <span class="n">ThisChar</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
</div>
<p>With this, we have the complete lexer for the basic Kaleidoscope
language (the <a class="reference external" href="LangImpl02.html#full-code-listing">full code listing</a> for the Lexer
is available in the <a class="reference external" href="LangImpl02.html">next chapter</a> of the tutorial).
Next we’ll <a class="reference external" href="LangImpl02.html">build a simple parser that uses this to build an Abstract
Syntax Tree</a>. When we have that, we’ll include a
driver so that you can use the lexer and parser together.</p>
<p><a class="reference external" href="LangImpl02.html">Next: Implementing a Parser and AST</a></p>
</div>
</div>
<div class="clearer"></div>
</div>
</div>
</div>
<div class="clearer"></div>
</div>
<div class="related" role="navigation" aria-label="related navigation">
<h3>Navigation</h3>
<ul>
<li class="right" style="margin-right: 10px">
<a href="../../genindex.html" title="General Index"
>index</a></li>
<li class="right" >
<a href="LangImpl02.html" title="2. Kaleidoscope: Implementing a Parser and AST"
>next</a> |</li>
<li class="right" >
<a href="index.html" title="My First Language Frontend with LLVM Tutorial"
>previous</a> |</li>
<li><a href="https://llvm.org/">LLVM Home</a> | </li>
<li><a href="../../index.html">Documentation</a>»</li>
<li class="nav-item nav-item-1"><a href="../../GettingStartedTutorials.html" >Getting Started/Tutorials</a> »</li>
<li class="nav-item nav-item-2"><a href="../index.html" >LLVM Tutorial: Table of Contents</a> »</li>
<li class="nav-item nav-item-3"><a href="index.html" >My First Language Frontend with LLVM Tutorial</a> »</li>
<li class="nav-item nav-item-this"><a href=""><span class="section-number">1. </span>Kaleidoscope: Kaleidoscope Introduction and the Lexer</a></li>
</ul>
</div>
<div class="footer" role="contentinfo">
© Copyright 2003-2021, LLVM Project.
Last updated on 2021-09-18.
Created using <a href="https://www.sphinx-doc.org/">Sphinx</a> 3.5.4.
</div>
</body>
</html>
|