Date: Mon, 8 Apr 2013 18:41:23 +0000 Subject: Vendor import of llvm trunk r178860: http://llvm.org/svn/llvm-project/llvm/trunk@178860 --- docs/tutorial/OCamlLangImpl2.html | 1043 ------------------------------------- 1 file changed, 1043 deletions(-) delete mode 100644 docs/tutorial/OCamlLangImpl2.html (limited to 'docs/tutorial/OCamlLangImpl2.html') diff --git a/docs/tutorial/OCamlLangImpl2.html b/docs/tutorial/OCamlLangImpl2.html deleted file mode 100644 index 9bb4c40361c5..000000000000 --- a/docs/tutorial/OCamlLangImpl2.html +++ /dev/null @@ -1,1043 +0,0 @@ - - - - - Kaleidoscope: Implementing a Parser and AST - - - - - - - - -

Kaleidoscope: Implementing a Parser and AST

- -

Up to Tutorial Index
Chapter 2 -
-
Chapter 3: Code generation to LLVM IR

- -

- Written by Chris Lattner - and Erick Tryzelaar -

- - -

Chapter 2 Introduction

- - -

- -

Welcome to Chapter 2 of the "Implementing a language -with LLVM in Objective Caml" tutorial. This chapter shows you how to use -the lexer, built in Chapter 1, to build a -full parser for our -Kaleidoscope language. Once we have a parser, we'll define and build an Abstract Syntax -Tree (AST).

- -

The parser we will build uses a combination of Recursive Descent -Parsing and Operator-Precedence -Parsing 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.

- -

- - -

The Abstract Syntax Tree (AST)

- - -

- -

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:

- -

-(* expr - Base type for all expression nodes. *)
-type expr =
-  (* variant for numeric literals like "1.0". *)
-  | Number of float
-

- -

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.

- -

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: -

- -

-  (* 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
-

- -

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.

- -

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:

- -

-(* 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
-

- -

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.

- -

With this scaffolding, we can now talk about parsing expressions and function -bodies in Kaleidoscope.

- -

- - -

Parser Basics

- - -

- -

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:

- -

-  let x = Variable "x" in
-  let y = Variable "y" in
-  let result = Binary ('+', x, y) in
-  ...
-

- -

-The error handling routines make use of the builtin Stream.Failure and -Stream.Errors. Stream.Failure is raised when the parser is -unable to find any matching token in the first position of a pattern. -Stream.Error 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.

- -

With these basic types and exceptions, we can implement the first -piece of our grammar: numeric literals.

- -

- - -

Basic Expression Parsing

- - -

- -

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 -later in the tutorial. In order to parse an arbitrary primary expression, -we need to determine what sort of expression it is. For numeric literals, we -have:

- -

-(* primary
- *   ::= identifier
- *   ::= numberexpr
- *   ::= parenexpr *)
-parse_primary = parser
-  (* numberexpr ::= number *)
-  | [< 'Token.Number n >] -> Ast.Number n
-

- -

This routine is very simple: it expects to be called when the current token -is a Token.Number token. It takes the current number value, creates -a Ast.Number node, advances the lexer to the next token, and finally -returns.

- -

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:

- -

-  (* parenexpr ::= '(' expression ')' *)
-  | [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e
-

- -

This function illustrates a number of interesting things about the -parser:

- -

-1) It shows how we use the Stream.Error 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 token ?? "parse -error", where if the token before the ?? does not match, then -Stream.Error "parse error" will be raised.

- -

2) Another interesting aspect of this function is that it uses recursion by -calling Parser.parse_primary (we will soon see that -Parser.parse_primary can call Parser.parse_primary). 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.

- -

The next simple production is for handling variable references and function -calls:

- -

-  (* 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
-

- -

This routine follows the same style as the other routines. (It expects to be -called if the current token is a Token.Ident token). It also has -recursion and error handling. One interesting aspect of this is that it uses -look-ahead 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 Ast.Variable or Ast.Call node as appropriate. -

- -

We finish up by raising an exception if we received a token we didn't -expect:

- -

-  | [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
-

- -

Now that basic expressions are handled, we need to handle binary expressions. -They are a bit more complex.

- -

- - -

Binary Expression Parsing

- - -

- -

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 precedence than "+" (addition).

- -

There are many ways to handle this, but an elegant and efficient way is to -use Operator-Precedence -Parsing. This parsing technique uses the precedence of binary operators to -guide recursion. To start with, we need a table of precedences:

- -

-(* 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. *)
-  ...
-

- -

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 -Parser.precedence function returns the precedence for the current -token, or -1 if the token is not a binary operator. Having a Hashtbl.t -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 Hashtbl.t and do the comparisons in the -Parser.precedence function. (Or just use a fixed-size array).

- -

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. -

- -

-To start, an expression is a primary expression potentially followed by a -sequence of [binop,primaryexpr] pairs:

- -

-(* expression
- *   ::= primary binoprhs *)
-and parse_expr = parser
-  | [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream
-

- -

Parser.parse_bin_rhs 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 Parser.parse_bin_rhs and the current token is "+".

- -

The precedence value passed into Parser.parse_bin_rhs indicates the -minimal operator precedence that the function is allowed to eat. For -example, if the current pair stream is [+, x] and Parser.parse_bin_rhs -is passed in a precedence of 40, it will not consume any tokens (because the -precedence of '+' is only 20). With this in mind, Parser.parse_bin_rhs -starts with:

- -

-(* 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
-

- -

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:

- -

-        (* Eat the binop. *)
-        Stream.junk stream;
-
-        (* Okay, we know this is a binop. *)
-        let rhs =
-          match Stream.peek stream with
-          | Some (Token.Kwd c2) ->
-

- -

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.

- -

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):

- -

-              (* 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
-

- -

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:

- -

-          ... if body omitted ...
-        in
-
-        (* Merge lhs/rhs. *)
-        let lhs = Ast.Binary (c, lhs, rhs) in
-        parse_bin_rhs expr_prec lhs stream
-      end
-

- -

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.

- -

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):

- -

-          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 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
-

- -

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 Parser.parse_bin_rhs 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.

- -

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. -

- -

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.

- -

- - -

Parsing the Rest

- - -

- -

-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): -

- -

-(* 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")
-

- -

Given this, a function definition is very simple, just a prototype plus -an expression to implement the body:

- -

-(* definition ::= 'def' prototype expression *)
-let parse_definition = parser
-  | [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
-      Ast.Function (p, e)
-

- -

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:

- -

-(*  external ::= 'extern' prototype *)
-let parse_extern = parser
-  | [< 'Token.Extern; e=parse_prototype >] -> e
-

- -

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:

- -

-(* toplevelexpr ::= expression *)
-let parse_toplevel = parser
-  | [< e=parse_expr >] ->
-      (* Make an anonymous proto. *)
-      Ast.Function (Ast.Prototype ("", [||]), e)
-

- -

Now that we have all the pieces, let's build a little driver that will let us -actually execute this code we've built!

- -

- - -

The Driver

- - -

- -

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 below for full code in the "Top-Level -Parsing" section.

- -

-(* 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
-

- -

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.

- -

- - -

Conclusions

- - -

- -

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:

- -

-$ ./toy.byte
-ready> def foo(x y) x+foo(y, 4.0);
-Parsed a function definition.
-ready> def foo(x y) x+y y;
-Parsed a function definition.
-Parsed a top-level expr
-ready> def foo(x y) x+y );
-Parsed a function definition.
-Error: unknown token when expecting an expression
-ready> extern sin(a);
-ready> Parsed an extern
-ready> ^D
-$
-

- -

There is a lot of room for extension here. You can define new AST nodes, -extend the language in many ways, etc. In the -next installment, we will describe how to generate LLVM Intermediate -Representation (IR) from the AST.

- -

- - -

Full Code Listing

- - -

- -

-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:

- -

-# Compile
-ocamlbuild toy.byte
-# Run
-./toy.byte
-

- -

Here is the code:

- -

_tags:

-<{lexer,parser}.ml>: use_camlp4, pp(camlp4of)
-

token.ml:

-(*===----------------------------------------------------------------------===
- * 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
-

lexer.ml:

-(*===----------------------------------------------------------------------===
- * 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
-  | [< >] -> [< >]
-

ast.ml:

-(*===----------------------------------------------------------------------===
- * 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
-

parser.ml:

-(*===---------------------------------------------------------------------===
- * 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")
-
-(* definition ::= 'def' prototype expression *)
-let parse_definition = parser
-  | [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
-      Ast.Function (p, e)
-
-(* toplevelexpr ::= expression *)
-let parse_toplevel = parser
-  | [< e=parse_expr >] ->
-      (* Make an anonymous proto. *)
-      Ast.Function (Ast.Prototype ("", [||]), e)
-
-(*  external ::= 'extern' prototype *)
-let parse_extern = parser
-  | [< 'Token.Extern; e=parse_prototype >] -> e
-

toplevel.ml:

-(*===----------------------------------------------------------------------===
- * Top-Level parsing and JIT Driver
- *===----------------------------------------------------------------------===*)
-
-(* 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
-

toy.ml:

-(*===----------------------------------------------------------------------===
- * Main driver code.
- *===----------------------------------------------------------------------===*)
-
-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. *)
-
-  (* Prime the first token. *)
-  print_string "ready> "; flush stdout;
-  let stream = Lexer.lex (Stream.of_channel stdin) in
-
-  (* Run the main "interpreter loop" now. *)
-  Toplevel.main_loop stream;
-;;
-
-main ()
-

- -Next: Implementing Code Generation to LLVM IR -

- - -

- - Chris Lattner - Erick Tryzelaar
- The LLVM Compiler Infrastructure
- Last modified: $Date: 2012-05-03 00:46:36 +0200 (Thu, 03 May 2012) $ -

- - -- cgit v1.3