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diff --git a/docs/tutorial/LangImpl6.rst b/docs/tutorial/LangImpl6.rst new file mode 100644 index 0000000000..30f4e90d03 --- /dev/null +++ b/docs/tutorial/LangImpl6.rst @@ -0,0 +1,1728 @@ +============================================================ +Kaleidoscope: Extending the Language: User-defined Operators +============================================================ + +.. contents:: + :local: + +Written by `Chris Lattner <mailto:sabre@nondot.org>`_ + +Chapter 6 Introduction +====================== + +Welcome to Chapter 6 of the "`Implementing a language with +LLVM <index.html>`_" tutorial. At this point in our tutorial, we now +have a fully functional language that is fairly minimal, but also +useful. There is still one big problem with it, however. Our language +doesn't have many useful operators (like division, logical negation, or +even any comparisons besides less-than). + +This chapter of the tutorial takes a wild digression into adding +user-defined operators to the simple and beautiful Kaleidoscope +language. This digression now gives 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 to use +this as a way to show some interesting parsing techniques. + +At the end of this tutorial, we'll run through an example Kaleidoscope +application that `renders the Mandelbrot set <#example>`_. This gives an +example of what you can build with Kaleidoscope and its feature set. + +User-defined Operators: the Idea +================================ + +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 let the +user round out the set of operators that are supported. + +The point of going into user-defined operators in a tutorial like this +is to show the power and flexibility of using a hand-written parser. +Thus far, the parser we have been implementing uses recursive descent +for most parts of the grammar and operator precedence parsing for the +expressions. See `Chapter 2 <LangImpl2.html>`_ 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. + +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: + +:: + + # Logical unary not. + def unary!(v) + if v then + 0 + else + 1; + + # Define > with the same precedence as <. + def binary> 10 (LHS RHS) + 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); + +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! + +We will break down implementation of these features into two parts: +implementing support for user-defined binary operators and adding unary +operators. + +User-defined Binary Operators +============================= + +Adding support for user-defined binary operators is pretty simple with +our current framework. We'll first add support for the unary/binary +keywords: + +.. code-block:: c++ + + enum Token { + ... + // operators + tok_binary = -11, tok_unary = -12 + }; + ... + static int gettok() { + ... + if (IdentifierStr == "for") return tok_for; + if (IdentifierStr == "in") return tok_in; + if (IdentifierStr == "binary") return tok_binary; + if (IdentifierStr == "unary") return tok_unary; + return tok_identifier; + +This just adds lexer support for the unary and binary keywords, like we +did in `previous chapters <LangImpl5.html#iflexer>`_. One nice thing +about our current AST, is that we represent binary operators with full +generalisation by using their ASCII code as the opcode. For our extended +operators, we'll use this same representation, so we don't need any new +AST or parser support. + +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 our grammar so far, the "name" for the function +definition is parsed as the "prototype" production and into the +``PrototypeAST`` AST node. To represent our new user-defined operators +as prototypes, we have to extend the ``PrototypeAST`` AST node like +this: + +.. code-block:: c++ + + /// 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; + bool isOperator; + unsigned Precedence; // Precedence if a binary op. + public: + PrototypeAST(const std::string &name, const std::vector<std::string> &args, + bool isoperator = false, unsigned prec = 0) + : Name(name), Args(args), isOperator(isoperator), Precedence(prec) {} + + 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; } + + Function *Codegen(); + }; + +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 (as you'll see below, it just doesn't apply for unary +operators). Now that we have a way to represent the prototype for a +user-defined operator, we need to parse it: + +.. code-block:: c++ + + /// prototype + /// ::= id '(' id* ')' + /// ::= binary LETTER number? (id, id) + static PrototypeAST *ParsePrototype() { + std::string FnName; + + unsigned Kind = 0; // 0 = identifier, 1 = unary, 2 = binary. + unsigned BinaryPrecedence = 30; + + switch (CurTok) { + default: + return ErrorP("Expected function name in prototype"); + case tok_identifier: + FnName = IdentifierStr; + Kind = 0; + getNextToken(); + break; + case tok_binary: + getNextToken(); + if (!isascii(CurTok)) + return ErrorP("Expected binary operator"); + FnName = "binary"; + FnName += (char)CurTok; + Kind = 2; + getNextToken(); + + // Read the precedence if present. + if (CurTok == tok_number) { + if (NumVal < 1 || NumVal > 100) + return ErrorP("Invalid precedecnce: must be 1..100"); + BinaryPrecedence = (unsigned)NumVal; + getNextToken(); + } + break; + } + + if (CurTok != '(') + return ErrorP("Expected '(' in prototype"); + + std::vector<std::string> ArgNames; + while (getNextToken() == tok_identifier) + ArgNames.push_back(IdentifierStr); + if (CurTok != ')') + return ErrorP("Expected ')' in prototype"); + + // success. + getNextToken(); // eat ')'. + + // Verify right number of names for operator. + if (Kind && ArgNames.size() != Kind) + return ErrorP("Invalid number of operands for operator"); + + return new PrototypeAST(FnName, ArgNames, Kind != 0, BinaryPrecedence); + } + +This is all fairly straightforward parsing code, and we have already +seen a lot of similar code in the past. One interesting part about the +code above is the couple lines that set up ``FnName`` for binary +operators. This builds names like "binary@" for a newly defined "@" +operator. This then takes advantage of the fact that symbol names in the +LLVM symbol table are allowed to have any character in them, including +embedded nul characters. + +The next interesting thing to add, is codegen support for these binary +operators. Given our current structure, this is a simple addition of a +default case for our existing binary operator node: + +.. code-block:: c++ + + Value *BinaryExprAST::Codegen() { + Value *L = LHS->Codegen(); + Value *R = RHS->Codegen(); + if (L == 0 || R == 0) return 0; + + switch (Op) { + case '+': return Builder.CreateFAdd(L, R, "addtmp"); + case '-': return Builder.CreateFSub(L, R, "subtmp"); + case '*': return Builder.CreateFMul(L, R, "multmp"); + case '<': + L = Builder.CreateFCmpULT(L, R, "cmptmp"); + // Convert bool 0/1 to double 0.0 or 1.0 + return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()), + "booltmp"); + default: break; + } + + // If it wasn't a builtin binary operator, it must be a user defined one. Emit + // a call to it. + Function *F = TheModule->getFunction(std::string("binary")+Op); + assert(F && "binary operator not found!"); + + Value *Ops[2] = { L, R }; + return Builder.CreateCall(F, Ops, "binop"); + } + +As you can see above, the new code is actually really simple. It just +does a lookup for the appropriate operator in the symbol table and +generates a function call to it. Since user-defined operators are just +built as normal functions (because the "prototype" boils down to a +function with the right name) everything falls into place. + +The final piece of code we are missing, is a bit of top-level magic: + +.. code-block:: c++ + + Function *FunctionAST::Codegen() { + NamedValues.clear(); + + Function *TheFunction = Proto->Codegen(); + if (TheFunction == 0) + return 0; + + // If this is an operator, install it. + if (Proto->isBinaryOp()) + BinopPrecedence[Proto->getOperatorName()] = Proto->getBinaryPrecedence(); + + // Create a new basic block to start insertion into. + BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction); + Builder.SetInsertPoint(BB); + + if (Value *RetVal = Body->Codegen()) { + ... + +Basically, before codegening a function, if it is a user-defined +operator, we register it in the precedence table. This allows the binary +operator parsing logic we already have in place to handle it. Since we +are working on a fully-general operator precedence parser, this is all +we need to do to "extend the grammar". + +Now we have useful user-defined binary operators. This builds a lot on +the previous framework we built for other operators. Adding unary +operators is a bit more challenging, because we don't have any framework +for it yet - lets see what it takes. + +User-defined Unary Operators +============================ + +Since we don't currently support unary operators in the Kaleidoscope +language, we'll need to add everything to support them. Above, we added +simple support for the 'unary' keyword to the lexer. In addition to +that, we need an AST node: + +.. code-block:: c++ + + /// UnaryExprAST - Expression class for a unary operator. + class UnaryExprAST : public ExprAST { + char Opcode; + ExprAST *Operand; + public: + UnaryExprAST(char opcode, ExprAST *operand) + : Opcode(opcode), Operand(operand) {} + virtual Value *Codegen(); + }; + +This AST node is very simple and obvious by now. It directly mirrors the +binary operator AST node, except that it only has one child. With this, +we need to add the parsing logic. Parsing a unary operator is pretty +simple: we'll add a new function to do it: + +.. code-block:: c++ + + /// unary + /// ::= primary + /// ::= '!' unary + static ExprAST *ParseUnary() { + // If the current token is not an operator, it must be a primary expr. + if (!isascii(CurTok) || CurTok == '(' || CurTok == ',') + return ParsePrimary(); + + // If this is a unary operator, read it. + int Opc = CurTok; + getNextToken(); + if (ExprAST *Operand = ParseUnary()) + return new UnaryExprAST(Opc, Operand); + return 0; + } + +The grammar we add is pretty straightforward here. If we see a unary +operator when parsing a primary operator, we eat the operator as a +prefix and parse the remaining piece as another unary operator. This +allows us to handle multiple unary operators (e.g. "!!x"). Note that +unary operators can't have ambiguous parses like binary operators can, +so there is no need for precedence information. + +The problem with this function, is that we need to call ParseUnary from +somewhere. To do this, we change previous callers of ParsePrimary to +call ParseUnary instead: + +.. code-block:: c++ + + /// binoprhs + /// ::= ('+' unary)* + static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) { + ... + // Parse the unary expression after the binary operator. + ExprAST *RHS = ParseUnary(); + if (!RHS) return 0; + ... + } + /// expression + /// ::= unary binoprhs + /// + static ExprAST *ParseExpression() { + ExprAST *LHS = ParseUnary(); + if (!LHS) return 0; + + return ParseBinOpRHS(0, LHS); + } + +With these two simple changes, we are now able to parse unary operators +and build the AST for them. Next up, we need to add parser support for +prototypes, to parse the unary operator prototype. We extend the binary +operator code above with: + +.. code-block:: c++ + + /// prototype + /// ::= id '(' id* ')' + /// ::= binary LETTER number? (id, id) + /// ::= unary LETTER (id) + static PrototypeAST *ParsePrototype() { + std::string FnName; + + unsigned Kind = 0; // 0 = identifier, 1 = unary, 2 = binary. + unsigned BinaryPrecedence = 30; + + switch (CurTok) { + default: + return ErrorP("Expected function name in prototype"); + case tok_identifier: + FnName = IdentifierStr; + Kind = 0; + getNextToken(); + break; + case tok_unary: + getNextToken(); + if (!isascii(CurTok)) + return ErrorP("Expected unary operator"); + FnName = "unary"; + FnName += (char)CurTok; + Kind = 1; + getNextToken(); + break; + case tok_binary: + ... + +As with binary operators, we name unary operators with a name that +includes the operator character. This assists us at code generation +time. Speaking of, the final piece we need to add is codegen support for +unary operators. It looks like this: + +.. code-block:: c++ + + Value *UnaryExprAST::Codegen() { + Value *OperandV = Operand->Codegen(); + if (OperandV == 0) return 0; + + Function *F = TheModule->getFunction(std::string("unary")+Opcode); + if (F == 0) + return ErrorV("Unknown unary operator"); + + return Builder.CreateCall(F, OperandV, "unop"); + } + +This code is similar to, but simpler than, the code for binary +operators. It is simpler primarily because it doesn't need to handle any +predefined operators. + +Kicking the Tires +================= + +It is somewhat hard to believe, but with a few simple extensions we've +covered in the last chapters, we have grown a real-ish language. With +this, we can do a lot of interesting things, including I/O, math, and a +bunch of other things. For example, we can now add a nice sequencing +operator (printd is defined to print out the specified value and a +newline): + +:: + + ready> extern printd(x); + Read extern: + declare double @printd(double) + + ready> def binary : 1 (x y) 0; # Low-precedence operator that ignores operands. + .. + ready> printd(123) : printd(456) : printd(789); + 123.000000 + 456.000000 + 789.000000 + Evaluated to 0.000000 + +We can also define a bunch of other "primitive" operations, such as: + +:: + + # Logical unary not. + def unary!(v) + if v then + 0 + else + 1; + + # Unary negate. + def unary-(v) + 0-v; + + # Define > with the same precedence as <. + def binary> 10 (LHS RHS) + RHS < LHS; + + # Binary logical or, which does not short circuit. + def binary| 5 (LHS RHS) + if LHS then + 1 + else if RHS then + 1 + else + 0; + + # Binary logical and, which does not short circuit. + def binary& 6 (LHS RHS) + if !LHS then + 0 + else + !!RHS; + + # Define = with slightly lower precedence than relationals. + def binary = 9 (LHS RHS) + !(LHS < RHS | LHS > RHS); + + # Define ':' for sequencing: as a low-precedence operator that ignores operands + # and just returns the RHS. + def binary : 1 (x y) y; + +Given the previous if/then/else support, we can also define interesting +functions for I/O. For example, the following prints out a character +whose "density" reflects the value passed in: the lower the value, the +denser the character: + +:: + + ready> + + extern putchard(char) + def printdensity(d) + if d > 8 then + putchard(32) # ' ' + else if d > 4 then + putchard(46) # '.' + else if d > 2 then + putchard(43) # '+' + else + putchard(42); # '*' + ... + ready> printdensity(1): printdensity(2): printdensity(3): + printdensity(4): printdensity(5): printdensity(9): + putchard(10); + **++. + Evaluated to 0.000000 + +Based on these simple primitive operations, we can start to define more +interesting things. For example, here's a little function that solves +for the number of iterations it takes a function in the complex plane to +converge: + +:: + + # Determine whether the specific location diverges. + # Solve for z = z^2 + c in the complex plane. + def mandleconverger(real imag iters creal cimag) + if iters > 255 | (real*real + imag*imag > 4) then + iters + else + mandleconverger(real*real - imag*imag + creal, + 2*real*imag + cimag, + iters+1, creal, cimag); + + # Return the number of iterations required for the iteration to escape + def mandleconverge(real imag) + mandleconverger(real, imag, 0, real, imag); + +This "``z = z2 + c``" function is a beautiful little creature that is +the basis for computation of the `Mandelbrot +Set <http://en.wikipedia.org/wiki/Mandelbrot_set>`_. Our +``mandelconverge`` function returns the number of iterations that it +takes for a complex orbit to escape, saturating to 255. This is not a +very useful function by itself, but if you plot its value over a +two-dimensional plane, you can see the Mandelbrot set. Given that we are +limited to using putchard here, our amazing graphical output is limited, +but we can whip together something using the density plotter above: + +:: + + # Compute and plot the mandlebrot set with the specified 2 dimensional range + # info. + def mandelhelp(xmin xmax xstep ymin ymax ystep) + for y = ymin, y < ymax, ystep in ( + (for x = xmin, x < xmax, xstep in + printdensity(mandleconverge(x,y))) + : putchard(10) + ) + + # mandel - This is a convenient helper function for plotting the mandelbrot set + # from the specified position with the specified Magnification. + def mandel(realstart imagstart realmag imagmag) + mandelhelp(realstart, realstart+realmag*78, realmag, + imagstart, imagstart+imagmag*40, imagmag); + +Given this, we can try plotting out the mandlebrot set! Lets try it out: + +:: + + ready> mandel(-2.3, -1.3, 0.05, 0.07); + *******************************+++++++++++************************************* + *************************+++++++++++++++++++++++******************************* + **********************+++++++++++++++++++++++++++++**************************** + *******************+++++++++++++++++++++.. ...++++++++************************* + *****************++++++++++++++++++++++.... ...+++++++++*********************** + ***************+++++++++++++++++++++++..... ...+++++++++********************* + **************+++++++++++++++++++++++.... ....+++++++++******************** + *************++++++++++++++++++++++...... .....++++++++******************* + ************+++++++++++++++++++++....... .......+++++++****************** + ***********+++++++++++++++++++.... ... .+++++++***************** + **********+++++++++++++++++....... .+++++++**************** + *********++++++++++++++........... ...+++++++*************** + ********++++++++++++............ ...++++++++************** + ********++++++++++... .......... .++++++++************** + *******+++++++++..... .+++++++++************* + *******++++++++...... ..+++++++++************* + *******++++++....... ..+++++++++************* + *******+++++...... ..+++++++++************* + *******.... .... ...+++++++++************* + *******.... . ...+++++++++************* + *******+++++...... ...+++++++++************* + *******++++++....... ..+++++++++************* + *******++++++++...... .+++++++++************* + *******+++++++++..... ..+++++++++************* + ********++++++++++... .......... .++++++++************** + ********++++++++++++............ ...++++++++************** + *********++++++++++++++.......... ...+++++++*************** + **********++++++++++++++++........ .+++++++**************** + **********++++++++++++++++++++.... ... ..+++++++**************** + ***********++++++++++++++++++++++....... .......++++++++***************** + ************+++++++++++++++++++++++...... ......++++++++****************** + **************+++++++++++++++++++++++.... ....++++++++******************** + ***************+++++++++++++++++++++++..... ...+++++++++********************* + *****************++++++++++++++++++++++.... ...++++++++*********************** + *******************+++++++++++++++++++++......++++++++************************* + *********************++++++++++++++++++++++.++++++++*************************** + *************************+++++++++++++++++++++++******************************* + ******************************+++++++++++++************************************ + ******************************************************************************* + ******************************************************************************* + ******************************************************************************* + Evaluated to 0.000000 + ready> mandel(-2, -1, 0.02, 0.04); + **************************+++++++++++++++++++++++++++++++++++++++++++++++++++++ + ***********************++++++++++++++++++++++++++++++++++++++++++++++++++++++++ + *********************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++. + *******************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++... + *****************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++..... + ***************++++++++++++++++++++++++++++++++++++++++++++++++++++++++........ + **************++++++++++++++++++++++++++++++++++++++++++++++++++++++........... + ************+++++++++++++++++++++++++++++++++++++++++++++++++++++.............. + ***********++++++++++++++++++++++++++++++++++++++++++++++++++........ . + **********++++++++++++++++++++++++++++++++++++++++++++++............. + ********+++++++++++++++++++++++++++++++++++++++++++.................. + *******+++++++++++++++++++++++++++++++++++++++....................... + ******+++++++++++++++++++++++++++++++++++........................... + *****++++++++++++++++++++++++++++++++............................ + *****++++++++++++++++++++++++++++............................... + ****++++++++++++++++++++++++++...... ......................... + ***++++++++++++++++++++++++......... ...... ........... + ***++++++++++++++++++++++............ + **+++++++++++++++++++++.............. + **+++++++++++++++++++................ + *++++++++++++++++++................. + *++++++++++++++++............ ... + *++++++++++++++.............. + *+++....++++................ + *.......... ........... + * + *.......... ........... + *+++....++++................ + *++++++++++++++.............. + *++++++++++++++++............ ... + *++++++++++++++++++................. + **+++++++++++++++++++................ + **+++++++++++++++++++++.............. + ***++++++++++++++++++++++............ + ***++++++++++++++++++++++++......... ...... ........... + ****++++++++++++++++++++++++++...... ......................... + *****++++++++++++++++++++++++++++............................... + *****++++++++++++++++++++++++++++++++............................ + ******+++++++++++++++++++++++++++++++++++........................... + *******+++++++++++++++++++++++++++++++++++++++....................... + ********+++++++++++++++++++++++++++++++++++++++++++.................. + Evaluated to 0.000000 + ready> mandel(-0.9, -1.4, 0.02, 0.03); + ******************************************************************************* + ******************************************************************************* + ******************************************************************************* + **********+++++++++++++++++++++************************************************ + *+++++++++++++++++++++++++++++++++++++++*************************************** + +++++++++++++++++++++++++++++++++++++++++++++********************************** + ++++++++++++++++++++++++++++++++++++++++++++++++++***************************** + ++++++++++++++++++++++++++++++++++++++++++++++++++++++************************* + +++++++++++++++++++++++++++++++++++++++++++++++++++++++++********************** + +++++++++++++++++++++++++++++++++.........++++++++++++++++++******************* + +++++++++++++++++++++++++++++++.... ......+++++++++++++++++++**************** + +++++++++++++++++++++++++++++....... ........+++++++++++++++++++************** + ++++++++++++++++++++++++++++........ ........++++++++++++++++++++************ + +++++++++++++++++++++++++++......... .. ...+++++++++++++++++++++********** + ++++++++++++++++++++++++++........... ....++++++++++++++++++++++******** + ++++++++++++++++++++++++............. .......++++++++++++++++++++++****** + +++++++++++++++++++++++............. ........+++++++++++++++++++++++**** + ++++++++++++++++++++++........... ..........++++++++++++++++++++++*** + ++++++++++++++++++++........... .........++++++++++++++++++++++* + ++++++++++++++++++............ ...........++++++++++++++++++++ + ++++++++++++++++............... .............++++++++++++++++++ + ++++++++++++++................. ...............++++++++++++++++ + ++++++++++++.................. .................++++++++++++++ + +++++++++.................. .................+++++++++++++ + ++++++........ . ......... ..++++++++++++ + ++............ ...... ....++++++++++ + .............. ...++++++++++ + .............. ....+++++++++ + .............. .....++++++++ + ............. ......++++++++ + ........... .......++++++++ + ......... ........+++++++ + ......... ........+++++++ + ......... ....+++++++ + ........ ...+++++++ + ....... ...+++++++ + ....+++++++ + .....+++++++ + ....+++++++ + ....+++++++ + ....+++++++ + Evaluated to 0.000000 + ready> ^D + +At this point, you may be starting to realize that Kaleidoscope is a +real and powerful language. It may not be self-similar :), but it can be +used to plot things that are! + +With this, we conclude the "adding user-defined operators" chapter of +the tutorial. We have successfully augmented our language, adding the +ability to extend the language in the library, and we have shown how +this can be used to build a simple but interesting end-user application +in Kaleidoscope. At this point, Kaleidoscope can build a variety of +applications that are functional and can call functions with +side-effects, but it can't actually define and mutate a variable itself. + +Strikingly, variable mutation is an important feature of some languages, +and it is not at all obvious how to `add support for mutable +variables <LangImpl7.html>`_ without having to add an "SSA construction" +phase to your front-end. In the next chapter, we will describe how you +can add variable mutation without building SSA in your front-end. + +Full Code Listing +================= + +Here is the complete code listing for our running example, enhanced with +the if/then/else and for expressions.. To build this example, use: + +.. code-block:: bash + + # Compile + clang++ -g toy.cpp `llvm-config --cppflags --ldflags --libs core jit native` -O3 -o toy + # Run + ./toy + +On some platforms, you will need to specify -rdynamic or +-Wl,--export-dynamic when linking. This ensures that symbols defined in +the main executable are exported to the dynamic linker and so are +available for symbol resolution at run time. This is not needed if you +compile your support code into a shared library, although doing that +will cause problems on Windows. + +Here is the code: + +.. code-block:: c++ + + #include "llvm/DerivedTypes.h" + #include "llvm/ExecutionEngine/ExecutionEngine.h" + #include "llvm/ExecutionEngine/JIT.h" + #include "llvm/IRBuilder.h" + #include "llvm/LLVMContext.h" + #include "llvm/Module.h" + #include "llvm/PassManager.h" + #include "llvm/Analysis/Verifier.h" + #include "llvm/Analysis/Passes.h" + #include "llvm/DataLayout.h" + #include "llvm/Transforms/Scalar.h" + #include "llvm/Support/TargetSelect.h" + #include <cstdio> + #include <string> + #include <map> + #include <vector> + using namespace llvm; + + //===----------------------------------------------------------------------===// + // Lexer + //===----------------------------------------------------------------------===// + + // The lexer returns tokens [0-255] if it is an unknown character, otherwise one + // of these for known things. + enum Token { + tok_eof = -1, + + // commands + tok_def = -2, tok_extern = -3, + + // primary + tok_identifier = -4, tok_number = -5, + + // control + tok_if = -6, tok_then = -7, tok_else = -8, + tok_for = -9, tok_in = -10, + + // operators + tok_binary = -11, tok_unary = -12 + }; + + static std::string IdentifierStr; // Filled in if tok_identifier + static double NumVal; // Filled in if tok_number + + /// gettok - Return the next token from standard input. + static int gettok() { + static int LastChar = ' '; + + // Skip any whitespace. + while (isspace(LastChar)) + LastChar = getchar(); + + if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]* + IdentifierStr = LastChar; + while (isalnum((LastChar = getchar()))) + IdentifierStr += LastChar; + + if (IdentifierStr == "def") return tok_def; + if (IdentifierStr == "extern") return tok_extern; + if (IdentifierStr == "if") return tok_if; + if (IdentifierStr == "then") return tok_then; + if (IdentifierStr == "else") return tok_else; + if (IdentifierStr == "for") return tok_for; + if (IdentifierStr == "in") return tok_in; + if (IdentifierStr == "binary") return tok_binary; + if (IdentifierStr == "unary") return tok_unary; + return tok_identifier; + } + + if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+ + std::string NumStr; + do { + NumStr += LastChar; + LastChar = getchar(); + } while (isdigit(LastChar) || LastChar == '.'); + + NumVal = strtod(NumStr.c_str(), 0); + return tok_number; + } + + if (LastChar == '#') { + // Comment until end of line. + do LastChar = getchar(); + while (LastChar != EOF && LastChar != '\n' && LastChar != '\r'); + + if (LastChar != EOF) + return gettok(); + } + + // Check for end of file. Don't eat the EOF. + if (LastChar == EOF) + return tok_eof; + + // Otherwise, just return the character as its ascii value. + int ThisChar = LastChar; + LastChar = getchar(); + return ThisChar; + } + + //===----------------------------------------------------------------------===// + // Abstract Syntax Tree (aka Parse Tree) + //===----------------------------------------------------------------------===// + + /// ExprAST - Base class for all expression nodes. + class ExprAST { + public: + virtual ~ExprAST() {} + virtual Value *Codegen() = 0; + }; + + /// NumberExprAST - Expression class for numeric literals like "1.0". + class NumberExprAST : public ExprAST { + double Val; + public: + NumberExprAST(double val) : Val(val) {} + virtual Value *Codegen(); + }; + + /// VariableExprAST - Expression class for referencing a variable, like "a". + class VariableExprAST : public ExprAST { + std::string Name; + public: + VariableExprAST(const std::string &name) : Name(name) {} + virtual Value *Codegen(); + }; + + /// UnaryExprAST - Expression class for a unary operator. + class UnaryExprAST : public ExprAST { + char Opcode; + ExprAST *Operand; + public: + UnaryExprAST(char opcode, ExprAST *operand) + : Opcode(opcode), Operand(operand) {} + virtual Value *Codegen(); + }; + + /// BinaryExprAST - Expression class for a binary operator. + class BinaryExprAST : public ExprAST { + char Op; + ExprAST *LHS, *RHS; + public: + BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs) + : Op(op), LHS(lhs), RHS(rhs) {} + virtual Value *Codegen(); + }; + + /// CallExprAST - Expression class for function calls. + class CallExprAST : public ExprAST { + std::string Callee; + std::vector<ExprAST*> Args; + public: + CallExprAST(const std::string &callee, std::vector<ExprAST*> &args) + : Callee(callee), Args(args) {} + virtual Value *Codegen(); + }; + + /// IfExprAST - Expression class for if/then/else. + class IfExprAST : public ExprAST { + ExprAST *Cond, *Then, *Else; + public: + IfExprAST(ExprAST *cond, ExprAST *then, ExprAST *_else) + : Cond(cond), Then(then), Else(_else) {} + virtual Value *Codegen(); + }; + + /// ForExprAST - Expression class for for/in. + class ForExprAST : public ExprAST { + std::string VarName; + ExprAST *Start, *End, *Step, *Body; + public: + ForExprAST(const std::string &varname, ExprAST *start, ExprAST *end, + ExprAST *step, ExprAST *body) + : VarName(varname), Start(start), End(end), Step(step), Body(body) {} + virtual Value *Codegen(); + }; + + /// PrototypeAST - This class represents the "prototype" for a function, + /// which captures its name, and its argument names (thus implicitly the number + /// of arguments the function takes), as well as if it is an operator. + class PrototypeAST { + std::string Name; + std::vector<std::string> Args; + bool isOperator; + unsigned Precedence; // Precedence if a binary op. + public: + PrototypeAST(const std::string &name, const std::vector<std::string> &args, + bool isoperator = false, unsigned prec = 0) + : Name(name), Args(args), isOperator(isoperator), Precedence(prec) {} + + 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; } + + Function *Codegen(); + }; + + /// FunctionAST - This class represents a function definition itself. + class FunctionAST { + PrototypeAST *Proto; + ExprAST *Body; + pu |