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| author | Chris Lattner <sabre@nondot.org> | 2007-11-01 06:49:54 +0000 |
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| committer | Chris Lattner <sabre@nondot.org> | 2007-11-01 06:49:54 +0000 |
| commit | c9d5d2c548533e22f8885b92e01494a4df8a4117 (patch) | |
| tree | ad052e095066f77a60822ecf6f189da3328f7a27 /docs/tutorial/LangImpl6.html | |
| parent | 0547bab214c65402cd80846e8bccb7535c0ddf09 (diff) | |
| download | external_llvm-c9d5d2c548533e22f8885b92e01494a4df8a4117.zip external_llvm-c9d5d2c548533e22f8885b92e01494a4df8a4117.tar.gz external_llvm-c9d5d2c548533e22f8885b92e01494a4df8a4117.tar.bz2 | |
Add the start of chapter 6, still much to go.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@43607 91177308-0d34-0410-b5e6-96231b3b80d8
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diff --git a/docs/tutorial/LangImpl6.html b/docs/tutorial/LangImpl6.html new file mode 100644 index 0000000..a8ef28f --- /dev/null +++ b/docs/tutorial/LangImpl6.html @@ -0,0 +1,227 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" + "http://www.w3.org/TR/html4/strict.dtd"> + +<html> +<head> + <title>Kaleidoscope: Extending the Language: Operator Overloading</title> + <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> + <meta name="author" content="Chris Lattner"> + <link rel="stylesheet" href="../llvm.css" type="text/css"> +</head> + +<body> + +<div class="doc_title">Kaleidoscope: Extending the Language: Operator Overloading</div> + +<div class="doc_author"> + <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p> +</div> + +<!-- *********************************************************************** --> +<div class="doc_section"><a name="intro">Part 6 Introduction</a></div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<p>Welcome to Part 6 of the "<a href="index.html">Implementing a language with +LLVM</a>" tutorial. At this point in our tutorial, we now have a fully +functional language that is fairly minimal, but also useful. One big problem +with it though is that it doesn't have many useful operators (like division, +logical negation, or even any comparisons other than less-than.</p> + +<p>This chapter of the tutorial takes a wild digression into adding operator +overloading to the simple and beautiful Kaleidoscope language, giving us a +simple and ugly language in some ways, but also a powerful one at the same time. +One of the great things about creating your own language is that you get to +decide what is good or bad. In this tutorial we'll assume that it is okay and +use this as a way to show some interesting parsing techniques.</p> + +</div> + +<!-- *********************************************************************** --> +<div class="doc_section"><a name="idea">Operator Overloading: the Idea</a></div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<p> +The operator overloading that we will add to Kaleidoscope is more general than +languages like C++. In C++, you are only allowed to redefine existing +operators: you can't programatically change the grammar, introduce new +operators, change precedence levels, etc. In this chapter, we will add this +capability to Kaleidoscope, which will allow us to round out the set of +operators that are supported, culminating in a more interesting example app.</p> + +<p>The point of going into operator overloading in a tutorial like this is to +show the power and flexibility of using a hand-written parser. The parser we +are using so far is using recursive descent for most parts of the grammar, and +operator precedence parsing for the expressions. See <a +href="LangImpl2.html">Chapter 2</a> for details. Without using operator +precedence parsing, it would be very difficult to allow the programmer to +introduce new operators into the grammar: the grammar is dynamically extensible +as the JIT runs.</p> + +<p>The two specific features we'll add are programmable unary operators (right +now, Kaleidoscope has no unary operators at all) as well as binary operators. +An example of this is:</p> + +<div class="doc_code"> +<pre> +# Logical unary not. +def unary!(v) + if v then + 0 + else + 1; + +# Define > with the same precedence as <. +def binary> 10 (LHS RHS) + !(LHS < RHS); # alternatively, could just use "RHS < LHS" + +# Binary "logical or", (note that it does not "short circuit") +def binary| 5 (LHS RHS) + if LHS then + 1 + else if RHS then + 1 + else + 0; + +# Define = with slightly lower precedence than relationals. +def binary= 9 (LHS RHS) + !(LHS < RHS | LHS > RHS); +</pre> +</div> + +<p>Many languages aspire to being able to implement their standard runtime +library in the language itself. In Kaleidoscope, we can implement significant +parts of the language in the library!</p> + +<p>We will break down implementation of these features into two parts: +implementing support for overloading of binary operators and adding unary +operators.</p> + +</div> + +<!-- *********************************************************************** --> +<div class="doc_section"><a name="binary">Overloading Binary Operators</a></div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<p>Adding support for overloaded binary operators is pretty simple with our +current framework. We'll first add support for the unary/binary keywords:</p> + +<div class="doc_code"> +<pre> +enum Token { + ... + <b>// operators + tok_binary = -11, tok_unary = -12</b> +}; +... +static int gettok() { +... + if (IdentifierStr == "for") return tok_for; + if (IdentifierStr == "in") return tok_in; + <b>if (IdentifierStr == "binary") return tok_binary; + if (IdentifierStr == "unary") return tok_unary;</b> + return tok_identifier; +</pre> +</div> + +<p>This just adds lexer support for the unary and binary keywords, like we +did in <a href="LangImpl5.html#iflexer">previous chapters</a>. One nice thing +about our current AST is that we represent binary operators fully generally +with their ASCII code as the opcode. For our extended operators, we'll use the +same representation, so we don't need any new AST or parser support.</p> + +<p>On the other hand, we have to be able to represent the definitions of these +new operators, in the "def binary| 5" part of the function definition. In the +grammar so far, the "name" for the function definition is parsed as the +"prototype" production and into the <tt>PrototypeAST</tt> AST node. To +represent our new user-defined operators as prototypes, we have to extend +the <tt>PrototypeAST</tt> AST node like this:</p> + +<div class="doc_code"> +<pre> +/// PrototypeAST - This class represents the "prototype" for a function, +/// which captures its argument names as well as if it is an operator. +class PrototypeAST { + std::string Name; + std::vector<std::string> Args; + <b>bool isOperator; + unsigned Precedence; // Precedence if a binary op.</b> +public: + PrototypeAST(const std::string &name, const std::vector<std::string> &args, + <b>bool isoperator = false, unsigned prec = 0</b>) + : Name(name), Args(args), <b>isOperator(isoperator), Precedence(prec)</b> {} + + <b>bool isUnaryOp() const { return isOperator && Args.size() == 1; } + bool isBinaryOp() const { return isOperator && Args.size() == 2; } + + char getOperatorName() const { + assert(isUnaryOp() || isBinaryOp()); + return Name[Name.size()-1]; + } + + unsigned getBinaryPrecedence() const { return Precedence; }</b> + + Function *Codegen(); +}; +</pre> +</div> + +<p>Basically, in addition to knowing a name for the prototype, we now keep track +of whether it was an operator, and if it was, what precedence level the operator +is at. The precedence is only used for binary operators.</p> + + +<p>...</p> + +</div> + + +<!-- *********************************************************************** --> +<div class="doc_section"><a name="code">Full Code Listing</a></div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<p> +Here is the complete code listing for our running example, enhanced with the +if/then/else and for expressions.. To build this example, use: +</p> + +<div class="doc_code"> +<pre> + # Compile + g++ -g toy.cpp `llvm-config --cppflags --ldflags --libs core jit native` -O3 -o toy + # Run + ./toy +</pre> +</div> + +<p>Here is the code:</p> + +<div class="doc_code"> +<pre> +</pre> +</div> + +</div> + +<!-- *********************************************************************** --> +<hr> +<address> + <a href="http://jigsaw.w3.org/css-validator/check/referer"><img + src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a> + <a href="http://validator.w3.org/check/referer"><img + src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a> + + <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) $ +</address> +</body> +</html> |