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diff --git a/docs/tutorial/OCamlLangImpl6.rst b/docs/tutorial/OCamlLangImpl6.rst new file mode 100644 index 0000000..36bffa8 --- /dev/null +++ b/docs/tutorial/OCamlLangImpl6.rst @@ -0,0 +1,1441 @@ +============================================================ +Kaleidoscope: Extending the Language: User-defined Operators +============================================================ + +.. contents:: + :local: + +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 <OCamlLangImpl2.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:: ocaml + + type token = + ... + (* operators *) + | Binary | Unary + + ... + + and lex_ident buffer = parser + ... + | "for" -> [< 'Token.For; stream >] + | "in" -> [< 'Token.In; stream >] + | "binary" -> [< 'Token.Binary; stream >] + | "unary" -> [< 'Token.Unary; stream >] + +This just adds lexer support for the unary and binary keywords, like we +did in `previous chapters <OCamlLangImpl5.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 +``Ast.Prototype`` AST node. To represent our new user-defined operators +as prototypes, we have to extend the ``Ast.Prototype`` AST node like +this: + +.. code-block:: ocaml + + (* 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 + | BinOpPrototype of string * string array * int + +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:: ocaml + + (* prototype + * ::= id '(' id* ')' + * ::= binary LETTER number? (id, id) + * ::= unary LETTER number? (id) *) + let parse_prototype = + let rec parse_args accumulator = parser + | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e + | [< >] -> accumulator + in + let parse_operator = parser + | [< 'Token.Unary >] -> "unary", 1 + | [< 'Token.Binary >] -> "binary", 2 + in + let parse_binary_precedence = parser + | [< 'Token.Number n >] -> int_of_float n + | [< >] -> 30 + 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)) + | [< (prefix, kind)=parse_operator; + 'Token.Kwd op ?? "expected an operator"; + (* Read the precedence if present. *) + binary_precedence=parse_binary_precedence; + 'Token.Kwd '(' ?? "expected '(' in prototype"; + args=parse_args []; + 'Token.Kwd ')' ?? "expected ')' in prototype" >] -> + let name = prefix ^ (String.make 1 op) in + let args = Array.of_list (List.rev args) in + + (* Verify right number of arguments for operator. *) + if Array.length args != kind + then raise (Stream.Error "invalid number of operands for operator") + else + if kind == 1 then + Ast.Prototype (name, args) + else + Ast.BinOpPrototype (name, args, binary_precedence) + | [< >] -> + raise (Stream.Error "expected function name in prototype") + +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 ``name`` 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:: ocaml + + let codegen_expr = function + ... + | Ast.Binary (op, lhs, rhs) -> + let lhs_val = codegen_expr lhs in + let rhs_val = codegen_expr rhs in + begin + match op with + | '+' -> build_add lhs_val rhs_val "addtmp" builder + | '-' -> build_sub lhs_val rhs_val "subtmp" builder + | '*' -> build_mul lhs_val rhs_val "multmp" builder + | '<' -> + (* Convert bool 0/1 to double 0.0 or 1.0 *) + let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in + build_uitofp i double_type "booltmp" builder + | _ -> + (* If it wasn't a builtin binary operator, it must be a user defined + * one. Emit a call to it. *) + let callee = "binary" ^ (String.make 1 op) in + let callee = + match lookup_function callee the_module with + | Some callee -> callee + | None -> raise (Error "binary operator not found!") + in + build_call callee [|lhs_val; rhs_val|] "binop" builder + end + +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:: ocaml + + let codegen_func the_fpm = function + | Ast.Function (proto, body) -> + Hashtbl.clear named_values; + let the_function = codegen_proto proto in + + (* If this is an operator, install it. *) + begin match proto with + | Ast.BinOpPrototype (name, args, prec) -> + let op = name.[String.length name - 1] in + Hashtbl.add Parser.binop_precedence op prec; + | _ -> () + end; + + (* Create a new basic block to start insertion into. *) + let bb = append_block context "entry" the_function in + position_at_end bb builder; + ... + +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:: ocaml + + type expr = + ... + (* variant for a unary operator. *) + | Unary of char * expr + ... + +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:: ocaml + + (* unary + * ::= primary + * ::= '!' unary *) + and parse_unary = parser + (* If this is a unary operator, read it. *) + | [< 'Token.Kwd op when op != '(' && op != ')'; operand=parse_expr >] -> + Ast.Unary (op, operand) + + (* If the current token is not an operator, it must be a primary expr. *) + | [< stream >] -> parse_primary stream + +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 ``parse_unary`` instead: + +.. code-block:: ocaml + + (* binoprhs + * ::= ('+' primary)* *) + and parse_bin_rhs expr_prec lhs stream = + ... + (* Parse the unary expression after the binary operator. *) + let rhs = parse_unary stream in + ... + + ... + + (* expression + * ::= primary binoprhs *) + and parse_expr = parser + | [< lhs=parse_unary; stream >] -> parse_bin_rhs 0 lhs stream + +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:: ocaml + + (* prototype + * ::= id '(' id* ')' + * ::= binary LETTER number? (id, id) + * ::= unary LETTER number? (id) *) + let parse_prototype = + let rec parse_args accumulator = parser + | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e + | [< >] -> accumulator + in + let parse_operator = parser + | [< 'Token.Unary >] -> "unary", 1 + | [< 'Token.Binary >] -> "binary", 2 + in + let parse_binary_precedence = parser + | [< 'Token.Number n >] -> int_of_float n + | [< >] -> 30 + 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)) + | [< (prefix, kind)=parse_operator; + 'Token.Kwd op ?? "expected an operator"; + (* Read the precedence if present. *) + binary_precedence=parse_binary_precedence; + 'Token.Kwd '(' ?? "expected '(' in prototype"; + args=parse_args []; + 'Token.Kwd ')' ?? "expected ')' in prototype" >] -> + let name = prefix ^ (String.make 1 op) in + let args = Array.of_list (List.rev args) in + + (* Verify right number of arguments for operator. *) + if Array.length args != kind + then raise (Stream.Error "invalid number of operands for operator") + else + if kind == 1 then + Ast.Prototype (name, args) + else + Ast.BinOpPrototype (name, args, binary_precedence) + | [< >] -> + raise (Stream.Error "expected function name in prototype") + +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:: ocaml + + let rec codegen_expr = function + ... + | Ast.Unary (op, operand) -> + let operand = codegen_expr operand in + let callee = "unary" ^ (String.make 1 op) in + let callee = + match lookup_function callee the_module with + | Some callee -> callee + | None -> raise (Error "unknown unary operator") + in + build_call callee [|operand|] "unop" builder + +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); + +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 = z\ :sup:`2`\ + 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 <OCamlLangImpl7.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 + ocamlbuild toy.byte + # Run + ./toy.byte + +Here is the code: + +\_tags: + :: + + <{lexer,parser}.ml>: use_camlp4, pp(camlp4of) + <*.{byte,native}>: g++, use_llvm, use_llvm_analysis + <*.{byte,native}>: use_llvm_executionengine, use_llvm_target + <*.{byte,native}>: use_llvm_scalar_opts, use_bindings + +myocamlbuild.ml: + .. code-block:: ocaml + + open Ocamlbuild_plugin;; + + ocaml_lib ~extern:true "llvm";; + ocaml_lib ~extern:true "llvm_analysis";; + ocaml_lib ~extern:true "llvm_executionengine";; + ocaml_lib ~extern:true "llvm_target";; + ocaml_lib ~extern:true "llvm_scalar_opts";; + + flag ["link"; "ocaml"; "g++"] (S[A"-cc"; A"g++"; A"-cclib"; A"-rdynamic"]);; + dep ["link"; "ocaml"; "use_bindings"] ["bindings.o"];; + +token.ml: + .. code-block:: ocaml + + (*===----------------------------------------------------------------------=== + * 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 + + (* control *) + | If | Then | Else + | For | In + + (* operators *) + | Binary | Unary + +lexer.ml: + .. code-block:: ocaml + + (*===----------------------------------------------------------------------=== + * 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 >] + | "if" -> [< 'Token.If; stream >] + | "then" -> [< 'Token.Then; stream >] + | "else" -> [< 'Token.Else; stream >] + | "for" -> [< 'Token.For; stream >] + | "in" -> [< 'Token.In; stream >] + | "binary" -> [< 'Token.Binary; stream >] + | "unary" -> [< 'Token.Unary; stream >] + | id -> [< 'Token.Ident id; stream >] + + and lex_comment = parser + | [< ' ('\n'); stream=lex >] -> stream + | [< 'c; e=lex_comment >] -> e + | [< >] -> [< >] + +ast.ml: + .. code-block:: ocaml + + (*===----------------------------------------------------------------------=== + * 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 unary operator. *) + | Unary of char * expr + + (* variant for a binary operator. *) + | Binary of char * expr * expr + + (* variant for function calls. *) + | Call of string * expr array + + (* variant for if/then/else. *) + | If of expr * expr * expr + + (* variant for for/in. *) + | For of string * expr * expr * expr option * expr + + (* 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 + | BinOpPrototype of string * string array * int + + (* func - This type represents a function definition itself. *) + type func = Function of proto * expr + +parser.ml: + .. code-block:: ocaml + + (*===---------------------------------------------------------------------=== + * 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 + * ::= ifexpr + * ::= forexpr *) + 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 + + (* ifexpr ::= 'if' expr 'then' expr 'else' expr *) + | [< 'Token.If; c=parse_expr; + 'Token.Then ?? "expected 'then'"; t=parse_expr; + 'Token.Else ?? "expected 'else'"; e=parse_expr >] -> + Ast.If (c, t, e) + + (* forexpr + ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression *) + | [< 'Token.For; + 'Token.Ident id ?? "expected identifier after for"; + 'Token.Kwd '=' ?? "expected '=' after for"; + stream >] -> + begin parser + | [< + start=parse_expr; + 'Token.Kwd ',' ?? "expected ',' after for"; + end_=parse_expr; + stream >] -> + let step = + begin parser + | [< 'Token.Kwd ','; step=parse_expr >] -> Some step + | [< >] -> None + end stream + in + begin parser + | [< 'Token.In; body=parse_expr >] -> + Ast.For (id, start, end_, step, body) + | [< >] -> + raise (Stream.Error "expected 'in' after for") + end stream + | [< >] -> + raise (Stream.Error "expected '=' after for") + end stream + + | [< >] -> raise (Stream.Error "unknown token when expecting an expression.") + + (* unary + * ::= primary + * ::= '!' unary *) + and parse_unary = parser + (* If this is a unary operator, read it. *) + | [< 'Token.Kwd op when op != '(' && op != ')'; operand=parse_expr >] -> + Ast.Unary (op, operand) + + (* If the current token is not an operator, it must be a primary expr. *) + | [< stream >] -> parse_primary stream + + (* 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 unary expression after the binary operator. *) + let rhs = parse_unary 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_unary; stream >] -> parse_bin_rhs 0 lhs stream + + (* prototype + * ::= id '(' id* ')' + * ::= binary LETTER number? (id, id) + * ::= unary LETTER number? (id) *) + let parse_prototype = + let rec parse_args accumulator = parser + | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e + | [< >] -> accumulator + in + let parse_operator = parser + | [< 'Token.Unary >] -> "unary", 1 + | [< 'Token.Binary >] -> "binary", 2 + in + let parse_binary_precedence = parser + | [< 'Token.Number n >] -> int_of_float n + | [< >] -> 30 + 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)) + | [< (prefix, kind)=parse_operator; + 'Token.Kwd op ?? "expected an operator"; + (* Read the precedence if present. *) + binary_precedence=parse_binary_precedence; + 'Token.Kwd '(' ?? "expected '(' in prototype"; + args=parse_args []; + 'Token.Kwd ')' ?? "expected ')' in prototype" >] -> + let name = prefix ^ (String.make 1 op) in + let args = Array.of_list (List.rev args) in + + (* Verify right number of arguments for operator. *) + if Array.length args != kind + then raise (Stream.Error "invalid number of operands for operator") + else + if kind == 1 then + Ast.Prototype (name, args) + else + Ast.BinOpPrototype (name, args, binary_precedence) + | [< >] -> + 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 + +codegen.ml: + .. code-block:: ocaml + + (*===----------------------------------------------------------------------=== + * Code Generation + *===----------------------------------------------------------------------===*) + + open Llvm + + exception Error of string + + let context = global_context () + let the_module = create_module context "my cool jit" + let builder = builder context + let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10 + let double_type = double_type context + + let rec codegen_expr = function + | Ast.Number n -> const_float double_type n + | Ast.Variable name -> + (try Hashtbl.find named_values name with + | Not_found -> raise (Error "unknown variable name")) + | Ast.Unary (op, operand) -> + let operand = codegen_expr operand in + let callee = "unary" ^ (String.make 1 op) in + let callee = + match lookup_function callee the_module with + | Some callee -> callee + | None -> raise (Error "unknown unary operator") + in + build_call callee [|operand|] "unop" builder + | Ast.Binary (op, lhs, rhs) -> + let lhs_val = codegen_expr lhs in + let rhs_val = codegen_expr rhs in + begin + match op with + | '+' -> build_add lhs_val rhs_val "addtmp" builder + | '-' -> build_sub lhs_val rhs_val "subtmp" builder + | '*' -> build_mul lhs_val rhs_val "multmp" builder + | '<' -> + (* Convert bool 0/1 to double 0.0 or 1.0 *) + let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in + build_uitofp i double_type "booltmp" builder + | _ -> + (* If it wasn't a builtin binary operator, it must be a user defined + * one. Emit a call to it. *) + let callee = "binary" ^ (String.make 1 op) in + let callee = + match lookup_function callee the_module with + | Some callee -> callee + | None -> raise (Error "binary operator not found!") + in + build_call callee [|lhs_val; rhs_val|] "binop" builder + end + | Ast.Call (callee, args) -> + (* Look up the name in the module table. *) + let callee = + match lookup_function callee the_module with + | Some callee -> callee + | None -> raise (Error "unknown function referenced") + in + let params = params callee in + + (* If argument mismatch error. *) + if Array.length params == Array.length args then () else + raise (Error "incorrect # arguments passed"); + let args = Array.map codegen_expr args in + build_call callee args "calltmp" builder + | Ast.If (cond, then_, else_) -> + let cond = codegen_expr cond in + + (* Convert condition to a bool by comparing equal to 0.0 *) + let zero = const_float double_type 0.0 in + let cond_val = build_fcmp Fcmp.One cond zero "ifcond" builder in + + (* Grab the first block so that we might later add the conditional branch + * to it at the end of the function. *) + let start_bb = insertion_block builder in + let the_function = block_parent start_bb in + + let then_bb = append_block context "then" the_function in + + (* Emit 'then' value. *) + position_at_end then_bb builder; + let then_val = codegen_expr then_ in + + (* Codegen of 'then' can change the current block, update then_bb for the + * phi. We create a new name because one is used for the phi node, and the + * other is used for the conditional branch. *) + let new_then_bb = insertion_block builder in + + (* Emit 'else' value. *) + let else_bb = append_block context "else" the_function in + position_at_end else_bb builder; + let else_val = codegen_expr else_ in + + (* Codegen of 'else' can change the current block, update else_bb for the + * phi. *) + let new_else_bb = insertion_block builder in + + (* Emit merge block. *) + let merge_bb = append_block context "ifcont" the_function in + position_at_end merge_bb builder; + let incoming = [(then_val, new_then_bb); (else_val, new_else_bb)] in + let phi = build_phi incoming "iftmp" builder in + + (* Return to the start block to add the conditional branch. *) + position_at_end start_bb builder; + ignore (build_cond_br cond_val then_bb else_bb builder); + + (* Set a unconditional branch at the end of the 'then' block and the + * 'else' block to the 'merge' block. *) + position_at_end new_then_bb builder; ignore (build_br merge_bb builder); + position_at_end new_else_bb builder; ignore (build_br merge_bb builder); + + (* Finally, set the builder to the end of the merge block. *) + position_at_end merge_bb builder; + + phi + | Ast.For (var_name, start, end_, step, body) -> + (* Emit the start code first, without 'variable' in scope. *) + let start_val = codegen_expr start in + + (* Make the new basic block for the loop header, inserting after current + * block. *) + let preheader_bb = insertion_block builder in + let the_function = block_parent preheader_bb in + let loop_bb = append_block context "loop" the_function in + + (* Insert an explicit fall through from the current block to the + * loop_bb. *) + ignore (build_br loop_bb builder); + + (* Start insertion in loop_bb. *) + position_at_end loop_bb builder; + + (* Start the PHI node with an entry for start. *) + let variable = build_phi [(start_val, preheader_bb)] var_name builder in + + (* Within the loop, the variable is defined equal to the PHI node. If it + * shadows an existing variable, we have to restore it, so save it + * now. *) + let old_val = + try Some (Hashtbl.find named_values var_name) with Not_found -> None + in + Hashtbl.add named_values var_name variable; + + (* Emit the body of the loop. This, like any other expr, can change the + * current BB. Note that we ignore the value computed by the body, but + * don't allow an error *) + ignore (codegen_expr body); + + (* Emit the step value. *) + let step_val = + match step with + | Some step -> codegen_expr step + (* If not specified, use 1.0. *) + | None -> const_float double_type 1.0 + in + + let next_var = build_add variable step_val "nextvar" builder in + + (* Compute the end condition. *) + let end_cond = codegen_expr end_ in + + (* Convert condition to a bool by comparing equal to 0.0. *) + let zero = const_float double_type 0.0 in + let end_cond = build_fcmp Fcmp.One end_cond zero "loopcond" builder in + + (* Create the "after loop" block and insert it. *) + let loop_end_bb = insertion_block builder in + let after_bb = append_block context "afterloop" the_function in + + (* Insert the conditional branch into the end of loop_end_bb. *) + ignore (build_cond_br end_cond loop_bb after_bb builder); + + (* Any new code will be inserted in after_bb. *) + position_at_end after_bb builder; + + (* Add a new entry to the PHI node for the backedge. *) + add_incoming (next_var, loop_end_bb) variable; + + (* Restore the unshadowed variable. *) + begin match old_val with + | Some old_val -> Hashtbl.add named_values var_name old_val + | None -> () + end; + + (* for expr always returns 0.0. *) + const_null double_type + + let codegen_proto = function + | Ast.Prototype (name, args) | Ast.BinOpPrototype (name, args, _) -> + (* Make the function type: double(double,double) etc. *) + let doubles = Array.make (Array.length args) double_type in + let ft = function_type double_type doubles in + let f = + match lookup_function name the_module with + | None -> declare_function name ft the_module + + (* If 'f' conflicted, there was already something named 'name'. If it + * has a body, don't allow redefinition or reextern. *) + | Some f -> + (* If 'f' already has a body, reject this. *) + if block_begin f <> At_end f then + raise (Error "redefinition of function"); + + (* If 'f' took a different number of arguments, reject. *) + if element_type (type_of f) <> ft then + raise (Error "redefinition of function with different # args"); + f + in + + (* Set names for all arguments. *) + Array.iteri (fun i a -> + let n = args.(i) in + set_value_name n a; + Hashtbl.add named_values n a; + ) (params f); + f + + let codegen_func the_fpm = function + | Ast.Function (proto, body) -> + Hashtbl.clear named_values; + let the_function = codegen_proto proto in + + (* If this is an operator, install it. *) + begin match proto with + | Ast.BinOpPrototype (name, args, prec) -> + let op = name.[String.length name - 1] in + Hashtbl.add Parser.binop_precedence op prec; + | _ -> () + end; + + (* Create a new basic block to start insertion into. *) + let bb = append_block context "entry" the_function in + position_at_end bb builder; + + try + let ret_val = codegen_expr body in + + (* Finish off the function. *) + let _ = build_ret ret_val builder in + + (* Validate the generated code, checking for consistency. *) + Llvm_analysis.assert_valid_function the_function; + + (* Optimize the function. *) + let _ = PassManager.run_function the_function the_fpm in + + the_function + with e -> + delete_function the_function; + raise e + +toplevel.ml: + .. code-block:: ocaml + + (*===----------------------------------------------------------------------=== + * Top-Level parsing and JIT Driver + *===----------------------------------------------------------------------===*) + + open Llvm + open Llvm_executionengine + + (* top ::= definition | external | expression | ';' *) + let rec main_loop the_fpm the_execution_engine stream = + match Stream.peek stream with + | None -> () + + (* ignore top-level semicolons. *) + | Some (Token.Kwd ';') -> + Stream.junk stream; + main_loop the_fpm the_execution_engine stream + + | Some token -> + begin + try match token with + | Token.Def -> + let e = Parser.parse_definition stream in + print_endline "parsed a function definition."; + dump_value (Codegen.codegen_func the_fpm e); + | Token.Extern -> + let e = Parser.parse_extern stream in + print_endline "parsed an extern."; + dump_value (Codegen.codegen_proto e); + | _ -> + (* Evaluate a top-level expression into an anonymous function. *) + let e = Parser.parse_toplevel stream in + print_endline "parsed a top-level expr"; + let the_function = Codegen.codegen_func the_fpm e in + dump_value the_function; + + (* JIT the function, returning a function pointer. *) + let result = ExecutionEngine.run_function the_function [||] + the_execution_engine in + + print_string "Evaluated to "; + print_float (GenericValue.as_float Codegen.double_type result); + print_newline (); + with Stream.Error s | Codegen.Error s -> + (* Skip token for error recovery. *) + Stream.junk stream; + print_endline s; + end; + print_string "ready> "; flush stdout; + main_loop the_fpm the_execution_engine stream + +toy.ml: + .. code-block:: ocaml + + (*===----------------------------------------------------------------------=== + * Main driver code. + *===----------------------------------------------------------------------===*) + + open Llvm + open Llvm_executionengine + open Llvm_target + open Llvm_scalar_opts + + let main () = + ignore (initialize_native_target ()); + + (* 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 + + (* Create the JIT. *) + let the_execution_engine = ExecutionEngine.create Codegen.the_module in + let the_fpm = PassManager.create_function Codegen.the_module in + + (* Set up the optimizer pipeline. Start with registering info about how the + * target lays out data structures. *) + DataLayout.add (ExecutionEngine.target_data the_execution_engine) the_fpm; + + (* Do simple "peephole" optimizations and bit-twiddling optzn. *) + add_instruction_combination the_fpm; + + (* reassociate expressions. *) + add_reassociation the_fpm; + + (* Eliminate Common SubExpressions. *) + add_gvn the_fpm; + + (* Simplify the control flow graph (deleting unreachable blocks, etc). *) + add_cfg_simplification the_fpm; + + ignore (PassManager.initialize the_fpm); + + (* Run the main "interpreter loop" now. *) + Toplevel.main_loop the_fpm the_execution_engine stream; + + (* Print out all the generated code. *) + dump_module Codegen.the_module + ;; + + main () + +bindings.c + .. code-block:: c + + #include <stdio.h> + + /* putchard - putchar that takes a double and returns 0. */ + extern double putchard(double X) { + putchar((char)X); + return 0; + } + + /* printd - printf that takes a double prints it as "%f\n", returning 0. */ + extern double printd(double X) { + printf("%f\n", X); + return 0; + } + +`Next: Extending the language: mutable variables / SSA +construction <OCamlLangImpl7.html>`_ + |
