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diff --git a/docs/tutorial/OCamlLangImpl2.html b/docs/tutorial/OCamlLangImpl2.html deleted file mode 100644 index dd7e07b422..0000000000 --- a/docs/tutorial/OCamlLangImpl2.html +++ /dev/null @@ -1,1043 +0,0 @@ -<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" - "http://www.w3.org/TR/html4/strict.dtd"> - -<html> -<head> - <title>Kaleidoscope: Implementing a Parser and AST</title> - <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> - <meta name="author" content="Chris Lattner"> - <meta name="author" content="Erick Tryzelaar"> - <link rel="stylesheet" href="../_static/llvm.css" type="text/css"> -</head> - -<body> - -<h1>Kaleidoscope: Implementing a Parser and AST</h1> - -<ul> -<li><a href="index.html">Up to Tutorial Index</a></li> -<li>Chapter 2 - <ol> - <li><a href="#intro">Chapter 2 Introduction</a></li> - <li><a href="#ast">The Abstract Syntax Tree (AST)</a></li> - <li><a href="#parserbasics">Parser Basics</a></li> - <li><a href="#parserprimexprs">Basic Expression Parsing</a></li> - <li><a href="#parserbinops">Binary Expression Parsing</a></li> - <li><a href="#parsertop">Parsing the Rest</a></li> - <li><a href="#driver">The Driver</a></li> - <li><a href="#conclusions">Conclusions</a></li> - <li><a href="#code">Full Code Listing</a></li> - </ol> -</li> -<li><a href="OCamlLangImpl3.html">Chapter 3</a>: Code generation to LLVM IR</li> -</ul> - -<div class="doc_author"> - <p> - Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> - and <a href="mailto:idadesub@users.sourceforge.net">Erick Tryzelaar</a> - </p> -</div> - -<!-- *********************************************************************** --> -<h2><a name="intro">Chapter 2 Introduction</a></h2> -<!-- *********************************************************************** --> - -<div> - -<p>Welcome to Chapter 2 of the "<a href="index.html">Implementing a language -with LLVM in Objective Caml</a>" tutorial. This chapter shows you how to use -the lexer, built in <a href="OCamlLangImpl1.html">Chapter 1</a>, to build a -full <a href="http://en.wikipedia.org/wiki/Parsing">parser</a> for our -Kaleidoscope language. Once we have a parser, we'll define and build an <a -href="http://en.wikipedia.org/wiki/Abstract_syntax_tree">Abstract Syntax -Tree</a> (AST).</p> - -<p>The parser we will build uses a combination of <a -href="http://en.wikipedia.org/wiki/Recursive_descent_parser">Recursive Descent -Parsing</a> and <a href= -"http://en.wikipedia.org/wiki/Operator-precedence_parser">Operator-Precedence -Parsing</a> to parse the Kaleidoscope language (the latter for -binary expressions and the former for everything else). Before we get to -parsing though, lets talk about the output of the parser: the Abstract Syntax -Tree.</p> - -</div> - -<!-- *********************************************************************** --> -<h2><a name="ast">The Abstract Syntax Tree (AST)</a></h2> -<!-- *********************************************************************** --> - -<div> - -<p>The AST for a program captures its behavior in such a way that it is easy for -later stages of the compiler (e.g. code generation) to interpret. We basically -want one object for each construct in the language, and the AST should closely -model the language. In Kaleidoscope, we have expressions, a prototype, and a -function object. We'll start with expressions first:</p> - -<div class="doc_code"> -<pre> -(* expr - Base type for all expression nodes. *) -type expr = - (* variant for numeric literals like "1.0". *) - | Number of float -</pre> -</div> - -<p>The code above shows the definition of the base ExprAST class and one -subclass which we use for numeric literals. The important thing to note about -this code is that the Number variant captures the numeric value of the -literal as an instance variable. This allows later phases of the compiler to -know what the stored numeric value is.</p> - -<p>Right now we only create the AST, so there are no useful functions on -them. It would be very easy to add a function to pretty print the code, -for example. Here are the other expression AST node definitions that we'll use -in the basic form of the Kaleidoscope language: -</p> - -<div class="doc_code"> -<pre> - (* variant for referencing a variable, like "a". *) - | Variable of string - - (* variant for a binary operator. *) - | Binary of char * expr * expr - - (* variant for function calls. *) - | Call of string * expr array -</pre> -</div> - -<p>This is all (intentionally) rather straight-forward: variables capture the -variable name, binary operators capture their opcode (e.g. '+'), and calls -capture a function name as well as a list of any argument expressions. One thing -that is nice about our AST is that it captures the language features without -talking about the syntax of the language. Note that there is no discussion about -precedence of binary operators, lexical structure, etc.</p> - -<p>For our basic language, these are all of the expression nodes we'll define. -Because it doesn't have conditional control flow, it isn't Turing-complete; -we'll fix that in a later installment. The two things we need next are a way -to talk about the interface to a function, and a way to talk about functions -themselves:</p> - -<div class="doc_code"> -<pre> -(* proto - This type represents the "prototype" for a function, which captures - * its name, and its argument names (thus implicitly the number of arguments the - * function takes). *) -type proto = Prototype of string * string array - -(* func - This type represents a function definition itself. *) -type func = Function of proto * expr -</pre> -</div> - -<p>In Kaleidoscope, functions are typed with just a count of their arguments. -Since all values are double precision floating point, the type of each argument -doesn't need to be stored anywhere. In a more aggressive and realistic -language, the "expr" variants would probably have a type field.</p> - -<p>With this scaffolding, we can now talk about parsing expressions and function -bodies in Kaleidoscope.</p> - -</div> - -<!-- *********************************************************************** --> -<h2><a name="parserbasics">Parser Basics</a></h2> -<!-- *********************************************************************** --> - -<div> - -<p>Now that we have an AST to build, we need to define the parser code to build -it. The idea here is that we want to parse something like "x+y" (which is -returned as three tokens by the lexer) into an AST that could be generated with -calls like this:</p> - -<div class="doc_code"> -<pre> - let x = Variable "x" in - let y = Variable "y" in - let result = Binary ('+', x, y) in - ... -</pre> -</div> - -<p> -The error handling routines make use of the builtin <tt>Stream.Failure</tt> and -<tt>Stream.Error</tt>s. <tt>Stream.Failure</tt> is raised when the parser is -unable to find any matching token in the first position of a pattern. -<tt>Stream.Error</tt> is raised when the first token matches, but the rest do -not. The error recovery in our parser will not be the best and is not -particular user-friendly, but it will be enough for our tutorial. These -exceptions make it easier to handle errors in routines that have various return -types.</p> - -<p>With these basic types and exceptions, we can implement the first -piece of our grammar: numeric literals.</p> - -</div> - -<!-- *********************************************************************** --> -<h2><a name="parserprimexprs">Basic Expression Parsing</a></h2> -<!-- *********************************************************************** --> - -<div> - -<p>We start with numeric literals, because they are the simplest to process. -For each production in our grammar, we'll define a function which parses that -production. We call this class of expressions "primary" expressions, for -reasons that will become more clear <a href="OCamlLangImpl6.html#unary"> -later in the tutorial</a>. In order to parse an arbitrary primary expression, -we need to determine what sort of expression it is. For numeric literals, we -have:</p> - -<div class="doc_code"> -<pre> -(* primary - * ::= identifier - * ::= numberexpr - * ::= parenexpr *) -parse_primary = parser - (* numberexpr ::= number *) - | [< 'Token.Number n >] -> Ast.Number n -</pre> -</div> - -<p>This routine is very simple: it expects to be called when the current token -is a <tt>Token.Number</tt> token. It takes the current number value, creates -a <tt>Ast.Number</tt> node, advances the lexer to the next token, and finally -returns.</p> - -<p>There are some interesting aspects to this. The most important one is that -this routine eats all of the tokens that correspond to the production and -returns the lexer buffer with the next token (which is not part of the grammar -production) ready to go. This is a fairly standard way to go for recursive -descent parsers. For a better example, the parenthesis operator is defined like -this:</p> - -<div class="doc_code"> -<pre> - (* parenexpr ::= '(' expression ')' *) - | [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e -</pre> -</div> - -<p>This function illustrates a number of interesting things about the -parser:</p> - -<p> -1) It shows how we use the <tt>Stream.Error</tt> exception. When called, this -function expects that the current token is a '(' token, but after parsing the -subexpression, it is possible that there is no ')' waiting. For example, if -the user types in "(4 x" instead of "(4)", the parser should emit an error. -Because errors can occur, the parser needs a way to indicate that they -happened. In our parser, we use the camlp4 shortcut syntax <tt>token ?? "parse -error"</tt>, where if the token before the <tt>??</tt> does not match, then -<tt>Stream.Error "parse error"</tt> will be raised.</p> - -<p>2) Another interesting aspect of this function is that it uses recursion by -calling <tt>Parser.parse_primary</tt> (we will soon see that -<tt>Parser.parse_primary</tt> can call <tt>Parser.parse_primary</tt>). This is -powerful because it allows us to handle recursive grammars, and keeps each -production very simple. Note that parentheses do not cause construction of AST -nodes themselves. While we could do it this way, the most important role of -parentheses are to guide the parser and provide grouping. Once the parser -constructs the AST, parentheses are not needed.</p> - -<p>The next simple production is for handling variable references and function -calls:</p> - -<div class="doc_code"> -<pre> - (* identifierexpr - * ::= identifier - * ::= identifier '(' argumentexpr ')' *) - | [< 'Token.Ident id; stream >] -> - let rec parse_args accumulator = parser - | [< e=parse_expr; stream >] -> - begin parser - | [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e - | [< >] -> e :: accumulator - end stream - | [< >] -> accumulator - in - let rec parse_ident id = parser - (* Call. *) - | [< 'Token.Kwd '('; - args=parse_args []; - 'Token.Kwd ')' ?? "expected ')'">] -> - Ast.Call (id, Array.of_list (List.rev args)) - - (* Simple variable ref. *) - | [< >] -> Ast.Variable id - in - parse_ident id stream -</pre> -</div> - -<p>This routine follows the same style as the other routines. (It expects to be -called if the current token is a <tt>Token.Ident</tt> token). It also has -recursion and error handling. One interesting aspect of this is that it uses -<em>look-ahead</em> to determine if the current identifier is a stand alone -variable reference or if it is a function call expression. It handles this by -checking to see if the token after the identifier is a '(' token, constructing -either a <tt>Ast.Variable</tt> or <tt>Ast.Call</tt> node as appropriate. -</p> - -<p>We finish up by raising an exception if we received a token we didn't -expect:</p> - -<div class="doc_code"> -<pre> - | [< >] -> raise (Stream.Error "unknown token when expecting an expression.") -</pre> -</div> - -<p>Now that basic expressions are handled, we need to handle binary expressions. -They are a bit more complex.</p> - -</div> - -<!-- *********************************************************************** --> -<h2><a name="parserbinops">Binary Expression Parsing</a></h2> -<!-- *********************************************************************** --> - -<div> - -<p>Binary expressions are significantly harder to parse because they are often -ambiguous. For example, when given the string "x+y*z", the parser can choose -to parse it as either "(x+y)*z" or "x+(y*z)". With common definitions from -mathematics, we expect the later parse, because "*" (multiplication) has -higher <em>precedence</em> than "+" (addition).</p> - -<p>There are many ways to handle this, but an elegant and efficient way is to -use <a href= -"http://en.wikipedia.org/wiki/Operator-precedence_parser">Operator-Precedence -Parsing</a>. This parsing technique uses the precedence of binary operators to -guide recursion. To start with, we need a table of precedences:</p> - -<div class="doc_code"> -<pre> -(* binop_precedence - This holds the precedence for each binary operator that is - * defined *) -let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10 - -(* precedence - Get the precedence of the pending binary operator token. *) -let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1 - -... - -let main () = - (* Install standard binary operators. - * 1 is the lowest precedence. *) - Hashtbl.add Parser.binop_precedence '<' 10; - Hashtbl.add Parser.binop_precedence '+' 20; - Hashtbl.add Parser.binop_precedence '-' 20; - Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *) - ... -</pre> -</div> - -<p>For the basic form of Kaleidoscope, we will only support 4 binary operators -(this can obviously be extended by you, our brave and intrepid reader). The -<tt>Parser.precedence</tt> function returns the precedence for the current -token, or -1 if the token is not a binary operator. Having a <tt>Hashtbl.t</tt> -makes it easy to add new operators and makes it clear that the algorithm doesn't -depend on the specific operators involved, but it would be easy enough to -eliminate the <tt>Hashtbl.t</tt> and do the comparisons in the -<tt>Parser.precedence</tt> function. (Or just use a fixed-size array).</p> - -<p>With the helper above defined, we can now start parsing binary expressions. -The basic idea of operator precedence parsing is to break down an expression -with potentially ambiguous binary operators into pieces. Consider ,for example, -the expression "a+b+(c+d)*e*f+g". Operator precedence parsing considers this -as a stream of primary expressions separated by binary operators. As such, -it will first parse the leading primary expression "a", then it will see the -pairs [+, b] [+, (c+d)] [*, e] [*, f] and [+, g]. Note that because parentheses -are primary expressions, the binary expression parser doesn't need to worry -about nested subexpressions like (c+d) at all. -</p> - -<p> -To start, an expression is a primary expression potentially followed by a -sequence of [binop,primaryexpr] pairs:</p> - -<div class="doc_code"> -<pre> -(* expression - * ::= primary binoprhs *) -and parse_expr = parser - | [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream -</pre> -</div> - -<p><tt>Parser.parse_bin_rhs</tt> is the function that parses the sequence of -pairs for us. It takes a precedence and a pointer to an expression for the part -that has been parsed so far. Note that "x" is a perfectly valid expression: As -such, "binoprhs" is allowed to be empty, in which case it returns the expression -that is passed into it. In our example above, the code passes the expression for -"a" into <tt>Parser.parse_bin_rhs</tt> and the current token is "+".</p> - -<p>The precedence value passed into <tt>Parser.parse_bin_rhs</tt> indicates the -<em>minimal operator precedence</em> that the function is allowed to eat. For -example, if the current pair stream is [+, x] and <tt>Parser.parse_bin_rhs</tt> -is passed in a precedence of 40, it will not consume any tokens (because the -precedence of '+' is only 20). With this in mind, <tt>Parser.parse_bin_rhs</tt> -starts with:</p> - -<div class="doc_code"> -<pre> -(* binoprhs - * ::= ('+' primary)* *) -and parse_bin_rhs expr_prec lhs stream = - match Stream.peek stream with - (* If this is a binop, find its precedence. *) - | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c -> - let token_prec = precedence c in - - (* If this is a binop that binds at least as tightly as the current binop, - * consume it, otherwise we are done. *) - if token_prec < expr_prec then lhs else begin -</pre> -</div> - -<p>This code gets the precedence of the current token and checks to see if if is -too low. Because we defined invalid tokens to have a precedence of -1, this -check implicitly knows that the pair-stream ends when the token stream runs out -of binary operators. If this check succeeds, we know that the token is a binary -operator and that it will be included in this expression:</p> - -<div class="doc_code"> -<pre> - (* Eat the binop. *) - Stream.junk stream; - - (* Okay, we know this is a binop. *) - let rhs = - match Stream.peek stream with - | Some (Token.Kwd c2) -> -</pre> -</div> - -<p>As such, this code eats (and remembers) the binary operator and then parses -the primary expression that follows. This builds up the whole pair, the first of -which is [+, b] for the running example.</p> - -<p>Now that we parsed the left-hand side of an expression and one pair of the -RHS sequence, we have to decide which way the expression associates. In -particular, we could have "(a+b) binop unparsed" or "a + (b binop unparsed)". -To determine this, we look ahead at "binop" to determine its precedence and -compare it to BinOp's precedence (which is '+' in this case):</p> - -<div class="doc_code"> -<pre> - (* If BinOp binds less tightly with rhs than the operator after - * rhs, let the pending operator take rhs as its lhs. *) - let next_prec = precedence c2 in - if token_prec < next_prec -</pre> -</div> - -<p>If the precedence of the binop to the right of "RHS" is lower or equal to the -precedence of our current operator, then we know that the parentheses associate -as "(a+b) binop ...". In our example, the current operator is "+" and the next -operator is "+", we know that they have the same precedence. In this case we'll -create the AST node for "a+b", and then continue parsing:</p> - -<div class="doc_code"> -<pre> - ... if body omitted ... - in - - (* Merge lhs/rhs. *) - let lhs = Ast.Binary (c, lhs, rhs) in - parse_bin_rhs expr_prec lhs stream - end -</pre> -</div> - -<p>In our example above, this will turn "a+b+" into "(a+b)" and execute the next -iteration of the loop, with "+" as the current token. The code above will eat, -remember, and parse "(c+d)" as the primary expression, which makes the -current pair equal to [+, (c+d)]. It will then evaluate the 'if' conditional above with -"*" as the binop to the right of the primary. In this case, the precedence of "*" is -higher than the precedence of "+" so the if condition will be entered.</p> - -<p>The critical question left here is "how can the if condition parse the right -hand side in full"? In particular, to build the AST correctly for our example, -it needs to get all of "(c+d)*e*f" as the RHS expression variable. The code to -do this is surprisingly simple (code from the above two blocks duplicated for -context):</p> - -<div class="doc_code"> -<pre> - match Stream.peek stream with - | Some (Token.Kwd c2) -> - (* If BinOp binds less tightly with rhs than the operator after - * rhs, let the pending operator take rhs as its lhs. *) - if token_prec < precedence c2 - then <b>parse_bin_rhs (token_prec + 1) rhs stream</b> - else rhs - | _ -> rhs - in - - (* Merge lhs/rhs. *) - let lhs = Ast.Binary (c, lhs, rhs) in - parse_bin_rhs expr_prec lhs stream - end -</pre> -</div> - -<p>At this point, we know that the binary operator to the RHS of our primary -has higher precedence than the binop we are currently parsing. As such, we know -that any sequence of pairs whose operators are all higher precedence than "+" -should be parsed together and returned as "RHS". To do this, we recursively -invoke the <tt>Parser.parse_bin_rhs</tt> function specifying "token_prec+1" as -the minimum precedence required for it to continue. In our example above, this -will cause it to return the AST node for "(c+d)*e*f" as RHS, which is then set -as the RHS of the '+' expression.</p> - -<p>Finally, on the next iteration of the while loop, the "+g" piece is parsed -and added to the AST. With this little bit of code (14 non-trivial lines), we -correctly handle fully general binary expression parsing in a very elegant way. -This was a whirlwind tour of this code, and it is somewhat subtle. I recommend -running through it with a few tough examples to see how it works. -</p> - -<p>This wraps up handling of expressions. At this point, we can point the -parser at an arbitrary token stream and build an expression from it, stopping -at the first token that is not part of the expression. Next up we need to -handle function definitions, etc.</p> - -</div> - -<!-- *********************************************************************** --> -<h2><a name="parsertop">Parsing the Rest</a></h2> -<!-- *********************************************************************** --> - -<div> - -<p> -The next thing missing is handling of function prototypes. In Kaleidoscope, -these are used both for 'extern' function declarations as well as function body -definitions. The code to do this is straight-forward and not very interesting -(once you've survived expressions): -</p> - -<div class="doc_code"> -<pre> -(* prototype - * ::= id '(' id* ')' *) -let parse_prototype = - let rec parse_args accumulator = parser - | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e - | [< >] -> accumulator - in - - parser - | [< 'Token.Ident id; - 'Token.Kwd '(' ?? "expected '(' in prototype"; - args=parse_args []; - 'Token.Kwd ')' ?? "expected ')' in prototype" >] -> - (* success. *) - Ast.Prototype (id, Array.of_list (List.rev args)) - - | [< >] -> - raise (Stream.Error "expected function name in prototype") -</pre> -</div> - -<p>Given this, a function definition is very simple, just a prototype plus -an expression to implement the body:</p> - -<div class="doc_code"> -<pre> -(* definition ::= 'def' prototype expression *) -let parse_definition = parser - | [< 'Token.Def; p=parse_prototype; e=parse_expr >] -> - Ast.Function (p, e) -</pre> -</div> - -<p>In addition, we support 'extern' to declare functions like 'sin' and 'cos' as -well as to support forward declaration of user functions. These 'extern's are just -prototypes with no body:</p> - -<div class="doc_code"> -<pre> -(* external ::= 'extern' prototype *) -let parse_extern = parser - | [< 'Token.Extern; e=parse_prototype >] -> e -</pre> -</div> - -<p>Finally, we'll also let the user type in arbitrary top-level expressions and -evaluate them on the fly. We will handle this by defining anonymous nullary -(zero argument) functions for them:</p> - -<div class="doc_code"> -<pre> -(* toplevelexpr ::= expression *) -let parse_toplevel = parser - | [< e=parse_expr >] -> - (* Make an anonymous proto. *) - Ast.Function (Ast.Prototype ("", [||]), e) -</pre> -</div> - -<p>Now that we have all the pieces, let's build a little driver that will let us -actually <em>execute</em> this code we've built!</p> - -</div> - -<!-- *********************************************************************** --> -<h2><a name="driver">The Driver</a></h2> -<!-- *********************************************************************** --> - -<div> - -<p>The driver for this simply invokes all of the parsing pieces with a top-level -dispatch loop. There isn't much interesting here, so I'll just include the -top-level loop. See <a href="#code">below</a> for full code in the "Top-Level -Parsing" section.</p> - -<div class="doc_code"> -<pre> -(* top ::= definition | external | expression | ';' *) -let rec main_loop stream = - match Stream.peek stream with - | None -> () - - (* ignore top-level semicolons. *) - | Some (Token.Kwd ';') -> - Stream.junk stream; - main_loop stream - - | Some token -> - begin - try match token with - | Token.Def -> - ignore(Parser.parse_definition stream); - print_endline "parsed a function definition."; - | Token.Extern -> - ignore(Parser.parse_extern stream); - print_endline "parsed an extern."; - | _ -> - (* Evaluate a top-level expression into an anonymous function. *) - ignore(Parser.parse_toplevel stream); - print_endline "parsed a top-level expr"; - with Stream.Error s -> - (* Skip token for error recovery. *) - Stream.junk stream; - print_endline s; - end; - print_string "ready> "; flush stdout; - main_loop stream -</pre> -</div> - -<p>The most interesting part of this is that we ignore top-level semicolons. -Why is this, you ask? The basic reason is that if you type "4 + 5" at the -command line, the parser doesn't know whether that is the end of what you will type -or not. For example, on the next line you could type "def foo..." in which case -4+5 is the end of a top-level expression. Alternatively you could type "* 6", -which would continue the expression. Having top-level semicolons allows you to -type "4+5;", and the parser will know you are done.</p> - -</div> - -<!-- *********************************************************************** --> -<h2><a name="conclusions">Conclusions</a></h2> -<!-- *********************************************************************** --> - -<div> - -<p>With just under 300 lines of commented code (240 lines of non-comment, -non-blank code), we fully defined our minimal language, including a lexer, -parser, and AST builder. With this done, the executable will validate -Kaleidoscope code and tell us if it is grammatically invalid. For -example, here is a sample interaction:</p> - -<div class="doc_code"> -<pre> -$ <b>./toy.byte</b> -ready> <b>def foo(x y) x+foo(y, 4.0);</b> -Parsed a function definition. -ready> <b>def foo(x y) x+y y;</b> -Parsed a function definition. -Parsed a top-level expr -ready> <b>def foo(x y) x+y );</b> -Parsed a function definition. -Error: unknown token when expecting an expression -ready> <b>extern sin(a);</b> -ready> Parsed an extern -ready> <b>^D</b> -$ -</pre> -</div> - -<p>There is a lot of room for extension here. You can define new AST nodes, -extend the language in many ways, etc. In the <a href="OCamlLangImpl3.html"> -next installment</a>, we will describe how to generate LLVM Intermediate -Representation (IR) from the AST.</p> - -</div> - -<!-- *********************************************************************** --> -<h2><a name="code">Full Code Listing</a></h2> -<!-- *********************************************************************** --> - -<div> - -<p> -Here is the complete code listing for this and the previous chapter. -Note that it is fully self-contained: you don't need LLVM or any external -libraries at all for this. (Besides the ocaml standard libraries, of -course.) To build this, just compile with:</p> - -<div class="doc_code"> -<pre> -# Compile -ocamlbuild toy.byte -# Run -./toy.byte -</pre> -</div> - -<p>Here is the code:</p> - -<dl> -<dt>_tags:</dt> -<dd class="doc_code"> -<pre> -<{lexer,parser}.ml>: use_camlp4, pp(camlp4of) -</pre> -</dd> - -<dt>token.ml:</dt> -<dd class="doc_code"> -<pre> -(*===----------------------------------------------------------------------=== - * Lexer Tokens - *===----------------------------------------------------------------------===*) - -(* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of - * these others for known things. *) -type token = - (* commands *) - | Def | Extern - - (* primary *) - | Ident of string | Number of float - - (* unknown *) - | Kwd of char -</pre> -</dd> - -<dt>lexer.ml:</dt> -<dd class="doc_code"> -<pre> -(*===----------------------------------------------------------------------=== - * Lexer - *===----------------------------------------------------------------------===*) - -let rec lex = parser - (* Skip any whitespace. *) - | [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream - - (* identifier: [a-zA-Z][a-zA-Z0-9] *) - | [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] -> - let buffer = Buffer.create 1 in - Buffer.add_char buffer c; - lex_ident buffer stream - - (* number: [0-9.]+ *) - | [< ' ('0' .. '9' as c); stream >] -> - let buffer = Buffer.create 1 in - Buffer.add_char buffer c; - lex_number buffer stream - - (* Comment until end of line. *) - | [< ' ('#'); stream >] -> - lex_comment stream - - (* Otherwise, just return the character as its ascii value. *) - | [< 'c; stream >] -> - [< 'Token.Kwd c; lex stream >] - - (* end of stream. *) - | [< >] -> [< >] - -and lex_number buffer = parser - | [< ' ('0' .. '9' | '.' as c); stream >] -> - Buffer.add_char buffer c; - lex_number buffer stream - | [< stream=lex >] -> - [< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >] - -and lex_ident buffer = parser - | [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] -> - Buffer.add_char buffer c; - lex_ident buffer stream - | [< stream=lex >] -> - match Buffer.contents buffer with - | "def" -> [< 'Token.Def; stream >] - | "extern" -> [< 'Token.Extern; stream >] - | id -> [< 'Token.Ident id; stream >] - -and lex_comment = parser - | [< ' ('\n'); stream=lex >] -> stream - | [< 'c; e=lex_comment >] -> e - | [< >] -> [< >] -</pre> -</dd> - -<dt>ast.ml:</dt> -<dd class="doc_code"> -<pre> -(*===----------------------------------------------------------------------=== - * Abstract Syntax Tree (aka Parse Tree) - *===----------------------------------------------------------------------===*) - -(* expr - Base type for all expression nodes. *) -type expr = - (* variant for numeric literals like "1.0". *) - | Number of float - - (* variant for referencing a variable, like "a". *) - | Variable of string - - (* variant for a binary operator. *) - | Binary of char * expr * expr - - (* variant for function calls. *) - | Call of string * expr array - -(* proto - This type represents the "prototype" for a function, which captures - * its name, and its argument names (thus implicitly the number of arguments the - * function takes). *) -type proto = Prototype of string * string array - -(* func - This type represents a function definition itself. *) -type func = Function of proto * expr -</pre> -</dd> - -<dt>parser.ml:</dt> -<dd class="doc_code"> -<pre> -(*===---------------------------------------------------------------------=== - * Parser - *===---------------------------------------------------------------------===*) - -(* binop_precedence - This holds the precedence for each binary operator that is - * defined *) -let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10 - -(* precedence - Get the precedence of the pending binary operator token. *) -let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1 - -(* primary - * ::= identifier - * ::= numberexpr - * ::= parenexpr *) -let rec parse_primary = parser - (* numberexpr ::= number *) - | [< 'Token.Number n >] -> Ast.Number n - - (* parenexpr ::= '(' expression ')' *) - | [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e - - (* identifierexpr - * ::= identifier - * ::= identifier '(' argumentexpr ')' *) - | [< 'Token.Ident id; stream >] -> - let rec parse_args accumulator = parser - | [< e=parse_expr; stream >] -> - begin parser - | [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e - | [< >] -> e :: accumulator - end stream - | [< >] -> accumulator - in - let rec parse_ident id = parser - (* Call. *) - | [< 'Token.Kwd '('; - args=parse_args []; - 'Token.Kwd ')' ?? "expected ')'">] -> - Ast.Call (id, Array.of_list (List.rev args)) - - (* Simple variable ref. *) - | [< >] -> Ast.Variable id - in - parse_ident id stream - - | [< >] -> raise (Stream.Error "unknown token when expecting an expression.") - -(* binoprhs - * ::= ('+' primary)* *) -and parse_bin_rhs expr_prec lhs stream = - match Stream.peek stream with - (* If this is a binop, find its precedence. *) - | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c -> - let token_prec = precedence c in - - (* If this is a binop that binds at least as tightly as the current binop, - * consume it, otherwise we are done. *) - if token_prec < expr_prec then lhs else begin - (* Eat the binop. *) - Stream.junk stream; - - (* Parse the primary expression after the binary operator. *) - let rhs = parse_primary stream in - - (* Okay, we know this is a binop. *) - let rhs = - match Stream.peek stream with - | Some (Token.Kwd c2) -> - (* If BinOp binds less tightly with rhs than the operator after - * rhs, let the pending operator take rhs as its lhs. *) - let next_prec = precedence c2 in - if token_prec < next_prec - then parse_bin_rhs (token_prec + 1) rhs stream - else rhs - | _ -> rhs - in - - (* Merge lhs/rhs. *) - let lhs = Ast.Binary (c, lhs, rhs) in - parse_bin_rhs expr_prec lhs stream - end - | _ -> lhs - -(* expression - * ::= primary binoprhs *) -and parse_expr = parser - | [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream - -(* prototype - * ::= id '(' id* ')' *) -let parse_prototype = - let rec parse_args accumulator = parser - | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e - | [< >] -> accumulator - in - - parser - | [< 'Token.Ident id; - 'Token.Kwd '(' ?? "expected '(' in prototype"; - args=parse_args []; - 'Token.Kwd ')' ?? "expected ')' in prototype" >] -> - (* success. *) - Ast.Prototype (id, Array.of_list (List.rev args)) - - | [< >] -> - raise (Stream.Error "expected function name in prototype")< |