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- <title>Kaleidoscope: The basic language, with its lexer</title>
+ <title>Kaleidoscope: Tutorial Introduction and the Lexer</title>
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-<div class="doc_title">Kaleidoscope: The basic language, with its lexer</div>
+<h1>Kaleidoscope: Tutorial Introduction and the Lexer</h1>
<ul>
+<li><a href="index.html">Up to Tutorial Index</a></li>
<li>Chapter 1
<ol>
<li><a href="#intro">Tutorial Introduction</a></li>
<li><a href="#lexer">The Lexer</a></li>
</ol>
</li>
+<li><a href="LangImpl2.html">Chapter 2</a>: Implementing a Parser and AST</li>
</ul>
<div class="doc_author">
</div>
<!-- *********************************************************************** -->
-<div class="doc_section"><a name="intro">Tutorial Introduction</a></div>
+<h2><a name="intro">Tutorial Introduction</a></h2>
<!-- *********************************************************************** -->
-<div class="doc_text">
+<div>
<p>Welcome to the "Implementing a language with LLVM" tutorial. This tutorial
-will run through implementation of a simple language, showing how fun and easy
-it can be. This tutorial will get you up and started and build a framework you
-can extend to other languages and to play with other things.
+runs through the implementation of a simple language, showing how fun and
+easy it can be. This tutorial will get you up and started as well as help to
+build a framework you can extend to other languages. The code in this tutorial
+can also be used as a playground to hack on other LLVM specific things.
</p>
+<p>
+The goal of this tutorial is to progressively unveil our language, describing
+how it is built up over time. This will let us cover a fairly broad range of
+language design and LLVM-specific usage issues, showing and explaining the code
+for it all along the way, without overwhelming you with tons of details up
+front.</p>
+
+<p>It is useful to point out ahead of time that this tutorial is really about
+teaching compiler techniques and LLVM specifically, <em>not</em> about teaching
+modern and sane software engineering principles. In practice, this means that
+we'll take a number of shortcuts to simplify the exposition. For example, the
+code leaks memory, uses global variables all over the place, doesn't use nice
+design patterns like <a
+href="http://en.wikipedia.org/wiki/Visitor_pattern">visitors</a>, etc... but it
+is very simple. If you dig in and use the code as a basis for future projects,
+fixing these deficiencies shouldn't be hard.</p>
+
+<p>I've tried to put this tutorial together in a way that makes chapters easy to
+skip over if you are already familiar with or are uninterested in the various
+pieces. The structure of the tutorial is:
+</p>
+
+<ul>
+<li><b><a href="#language">Chapter #1</a>: Introduction to the Kaleidoscope
+language, and the definition of its Lexer</b> - This shows where we are going
+and the basic functionality that we want it to do. In order to make this
+tutorial maximally understandable and hackable, we choose to implement
+everything in C++ instead of using lexer and parser generators. LLVM obviously
+works just fine with such tools, feel free to use one if you prefer.</li>
+<li><b><a href="LangImpl2.html">Chapter #2</a>: Implementing a Parser and
+AST</b> - With the lexer in place, we can talk about parsing techniques and
+basic AST construction. This tutorial describes recursive descent parsing and
+operator precedence parsing. Nothing in Chapters 1 or 2 is LLVM-specific,
+the code doesn't even link in LLVM at this point. :)</li>
+<li><b><a href="LangImpl3.html">Chapter #3</a>: Code generation to LLVM IR</b> -
+With the AST ready, we can show off how easy generation of LLVM IR really
+is.</li>
+<li><b><a href="LangImpl4.html">Chapter #4</a>: Adding JIT and Optimizer
+Support</b> - Because a lot of people are interested in using LLVM as a JIT,
+we'll dive right into it and show you the 3 lines it takes to add JIT support.
+LLVM is also useful in many other ways, but this is one simple and "sexy" way
+to shows off its power. :)</li>
+<li><b><a href="LangImpl5.html">Chapter #5</a>: Extending the Language: Control
+Flow</b> - With the language up and running, we show how to extend it with
+control flow operations (if/then/else and a 'for' loop). This gives us a chance
+to talk about simple SSA construction and control flow.</li>
+<li><b><a href="LangImpl6.html">Chapter #6</a>: Extending the Language:
+User-defined Operators</b> - This is a silly but fun chapter that talks about
+extending the language to let the user program define their own arbitrary
+unary and binary operators (with assignable precedence!). This lets us build a
+significant piece of the "language" as library routines.</li>
+<li><b><a href="LangImpl7.html">Chapter #7</a>: Extending the Language: Mutable
+Variables</b> - This chapter talks about adding user-defined local variables
+along with an assignment operator. The interesting part about this is how
+easy and trivial it is to construct SSA form in LLVM: no, LLVM does <em>not</em>
+require your front-end to construct SSA form!</li>
+<li><b><a href="LangImpl8.html">Chapter #8</a>: Conclusion and other useful LLVM
+tidbits</b> - This chapter wraps up the series by talking about potential
+ways to extend the language, but also includes a bunch of pointers to info about
+"special topics" like adding garbage collection support, exceptions, debugging,
+support for "spaghetti stacks", and a bunch of other tips and tricks.</li>
+
+</ul>
+
+<p>By the end of the tutorial, we'll have written a bit less than 700 lines of
+non-comment, non-blank, lines of code. With this small amount of code, we'll
+have built up a very reasonable compiler for a non-trivial language including
+a hand-written lexer, parser, AST, as well as code generation support with a JIT
+compiler. While other systems may have interesting "hello world" tutorials,
+I think the breadth of this tutorial is a great testament to the strengths of
+LLVM and why you should consider it if you're interested in language or compiler
+design.</p>
+
+<p>A note about this tutorial: we expect you to extend the language and play
+with it on your own. Take the code and go crazy hacking away at it, compilers
+don't need to be scary creatures - it can be a lot of fun to play with
+languages!</p>
+
</div>
<!-- *********************************************************************** -->
-<div class="doc_section"><a name="language">The Basic Language</a></div>
+<h2><a name="language">The Basic Language</a></h2>
<!-- *********************************************************************** -->
-<div class="doc_text">
+<div>
<p>This tutorial will be illustrated with a toy language that we'll call
-"<a href="http://en.wikipedia.org/wiki/Kaleidoscope">Kaleidoscope</a>".
+"<a 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 if/then/else, operator overloading, JIT compilation with
-a simple command line interface, etc.</p>
+Kaleidoscope to support the if/then/else construct, a for loop, user defined
+operators, JIT compilation with a simple command line interface, etc.</p>
-<p>Because we want to keep things simple, in Kaleidoscope the only datatype is a
+<p>Because we want to keep things simple, 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, A simple example computes <a
-href="http://en.wikipedia.org/wiki/Fibonacci_number">Fibonacci numbers</a>,
-which looks like this:</p>
+example, the following simple example computes <a
+href="http://en.wikipedia.org/wiki/Fibonacci_number">Fibonacci numbers:</a></p>
<div class="doc_code">
<pre>
</pre>
</div>
-<p>In the first incarnation of the language, we will only support basic
-arithmetic: if/then/else will be added in a future installment. Another
-interesting aspect of the first implementation is that it is a completely
-functional language, which does not allow you to have side-effects etc. We will
-eventually add side effects for those who prefer them.</p>
-
-<p>In order to make this tutorial
-maximally understandable and hackable, we choose to implement everything in C++
-instead of using lexer and parser generators. LLVM obviously works just fine
-with such tools, and making use of them doesn't impact the overall design.</p>
+<p>A more interesting example is included in Chapter 6 where we write a little
+Kaleidoscope application that <a href="LangImpl6.html#example">displays
+a Mandelbrot Set</a> at various levels of magnification.</p>
-<p>A note about this tutorial: we expect you to extend the language and play
-with it on your own. Take the code and go crazy hacking away at it. It can be
-a lot of fun to play with languages!</p>
+<p>Lets dive into the implementation of this language!</p>
</div>
<!-- *********************************************************************** -->
-<div class="doc_section"><a name="lexer">The Lexer</a></div>
+<h2><a name="lexer">The Lexer</a></h2>
<!-- *********************************************************************** -->
-<div class="doc_text">
+<div>
<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
</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
+or it will be an 'unknown' character like '+', which is returned as its ASCII
value. If the current token is an identifier, the <tt>IdentifierStr</tt>
global variable holds the name of the identifier. If the current token is a
numeric literal (like 1.0), <tt>NumVal</tt> holds its value. Note that we use
implementation :).
</p>
-<p>The actual implementation of the lexer is a single function <tt>gettok</tt>.
-<tt>gettok</tt> is called to return the next token from standard input. Its
-definition starts as:</p>
+<p>The actual implementation of the lexer is a single function named
+<tt>gettok</tt>. The <tt>gettok</tt> function is called to return the next token
+from standard input. Its definition starts as:</p>
<div class="doc_code">
<pre>
<p>
<tt>gettok</tt> works by calling the C <tt>getchar()</tt> 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
+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 it needs to do is recognize identifiers, and specific keywords
-like "def". Kaleidoscope does this with this simple loop:</p>
+<p>The next thing <tt>gettok</tt> needs to do is recognize identifiers and
+specific keywords like "def". Kaleidoscope does this with this simple loop:</p>
<div class="doc_code">
<pre>
</pre>
</div>
-<p>Note that it sets the '<tt>IdentifierStr</tt>' 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>
+<p>Note that this code sets the '<tt>IdentifierStr</tt>' 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="doc_code">
<pre>
if (LastChar == '#') {
// Comment until end of line.
do LastChar = getchar();
- while (LastChar != EOF && LastChar != '\n' & LastChar != '\r');
+ while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
if (LastChar != EOF)
return gettok();
</pre>
</div>
-<p>We handle comments by skipping to the end of the line and then returning the
-next comment. 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>
+<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="doc_code">
<pre>
</pre>
</div>
-<p>With this, we have the complete lexer for the basic Kaleidoscope language.
+<p>With this, we have the complete lexer for the basic Kaleidoscope language
+(the <a href="LangImpl2.html#code">full code listing</a> for the Lexer is
+available in the <a href="LangImpl2.html">next chapter</a> of the tutorial).
Next we'll <a href="LangImpl2.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>
+<a href="LangImpl2.html">Next: Implementing a Parser and AST</a>
</div>
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<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
- <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
- Last modified: $Date: 2007-10-17 11:05:13 -0700 (Wed, 17 Oct 2007) $
+ <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
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