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4 <html>
5 <head>
11 </head>
13 <body>
17 <ul>
20 <ol>
27 </ol>
28 </li>
30 Support</li>
31 </ul>
34 <p>
37 </p>
38 </div>
40 <!-- *********************************************************************** -->
42 <!-- *********************************************************************** -->
49 LLVM IR. This will teach you a little bit about how LLVM does things, as well
50 as demonstrate how easy it is to use. It's much more work to build a lexer and
51 parser than it is to generate LLVM IR code. :)
52 </p>
57 </div>
59 <!-- *********************************************************************** -->
61 <!-- *********************************************************************** -->
65 <p>
66 In order to generate LLVM IR, we want some simple setup to get started. First
67 we define virtual code generation (codegen) methods in each AST class:</p>
70 <pre>
71 let rec codegen_expr = function
72 | Ast.Number n -> ...
73 | Ast.Variable name -> ...
74 </pre>
75 </div>
78 along with all the things it depends on, and they all return an LLVM Value
82 of SSA values is that their value is computed as the related instruction
83 executes, and it does not get a new value until (and if) the instruction
84 re-executes. In other words, there is no way to "change" an SSA value. For
85 more information, please read up on <a
89 <p>The
90 second thing we want is an "Error" exception like we used for the parser, which
91 will be used to report errors found during code generation (for example, use of
92 an undeclared parameter):</p>
95 <pre>
96 exception Error of string
98 let the_module = create_module (global_context ()) "my cool jit"
99 let builder = builder (global_context ())
100 let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
101 let double_type = double_type context
102 </pre>
103 </div>
105 <p>The static variables will be used during code generation.
107 functions and global variables in a chunk of code. In many ways, it is the
108 top-level structure that the LLVM IR uses to contain code.</p>
111 generate LLVM instructions. Instances of the <a
113 class keep track of the current place to insert instructions and has methods to
114 create new instructions.</p>
117 in the current scope and what their LLVM representation is. (In other words, it
118 is a symbol table for the code). In this form of Kaleidoscope, the only things
119 that can be referenced are function parameters. As such, function parameters
120 will be in this map when generating code for their function body.</p>
122 <p>
123 With these basics in place, we can start talking about how to generate code for
126 that this has already been done, and we'll just use it to emit code.</p>
128 </div>
130 <!-- *********************************************************************** -->
132 <!-- *********************************************************************** -->
136 <p>Generating LLVM code for expression nodes is very straightforward: less
137 than 30 lines of commented code for all four of our expression nodes. First
138 we'll do numeric literals:</p>
141 <pre>
142 | Ast.Number n -> const_float double_type n
143 </pre>
144 </div>
146 <p>In the LLVM IR, numeric constants are represented with the
151 that constants are all uniqued together and shared. For this reason, the API
155 <pre>
156 | Ast.Variable name ->
157 (try Hashtbl.find named_values name with
159 </pre>
160 </div>
162 <p>References to variables are also quite simple using LLVM. In the simple
163 version of Kaleidoscope, we assume that the variable has already been emitted
164 somewhere and its value is available. In practice, the only values that can be
166 simply checks to see that the specified name is in the map (if not, an unknown
167 variable is being referenced) and returns the value for it. In future chapters,
173 <pre>
174 | Ast.Binary (op, lhs, rhs) ->
175 let lhs_val = codegen_expr lhs in
176 let rhs_val = codegen_expr rhs in
177 begin
178 match op with
184 let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
185 build_uitofp i double_type "booltmp" builder
187 end
188 </pre>
189 </div>
191 <p>Binary operators start to get more interesting. The basic idea here is that
192 we recursively emit code for the left-hand side of the expression, then the
193 right-hand side, then we compute the result of the binary expression. In this
194 code, we do a simple switch on the opcode to create the right LLVM instruction.
195 </p>
197 <p>In the example above, the LLVM builder class is starting to show its value.
198 IRBuilder knows where to insert the newly created instruction, all you have to
201 provide a name for the generated instruction.</p>
203 <p>One nice thing about LLVM is that the name is just a hint. For instance, if
204 the code above emits multiple "addtmp" variables, LLVM will automatically
205 provide each one with an increasing, unique numeric suffix. Local value names
206 for instructions are purely optional, but it makes it much easier to read the
207 IR dumps.</p>
210 strict rules: for example, the Left and Right operators of
212 type, and the result type of the add must match the operand types. Because
213 all values in Kaleidoscope are doubles, this makes for very simple code for add,
214 sub and mul.</p>
218 (a one bit integer). The problem with this is that Kaleidoscope wants the value to be a 0.0 or 1.0 value. In order to get these semantics, we combine the fcmp instruction with
220 converts its input integer into a floating point value by treating the input
221 as an unsigned value. In contrast, if we used the <a
226 <pre>
227 | Ast.Call (callee, args) ->
228 (* Look up the name in the module table. *)
229 let callee =
230 match lookup_function callee the_module with
231 | Some callee -> callee
233 in
234 let params = params callee in
236 (* If argument mismatch error. *)
237 if Array.length params == Array.length args then () else
238 raise (Error "incorrect # arguments passed");
239 let args = Array.map codegen_expr args in
240 build_call callee args "calltmp" builder
241 </pre>
242 </div>
244 <p>Code generation for function calls is quite straightforward with LLVM. The
245 code above initially does a function name lookup in the LLVM Module's symbol
246 table. Recall that the LLVM Module is the container that holds all of the
247 functions we are JIT'ing. By giving each function the same name as what the
248 user specifies, we can use the LLVM symbol table to resolve function names for
249 us.</p>
251 <p>Once we have the function to call, we recursively codegen each argument that
253 instruction</a>. Note that LLVM uses the native C calling conventions by
254 default, allowing these calls to also call into standard library functions like
257 <p>This wraps up our handling of the four basic expressions that we have so far
258 in Kaleidoscope. Feel free to go in and add some more. For example, by
260 several other interesting instructions that are really easy to plug into our
261 basic framework.</p>
263 </div>
265 <!-- *********************************************************************** -->
267 <!-- *********************************************************************** -->
271 <p>Code generation for prototypes and functions must handle a number of
272 details, which make their code less beautiful than expression code
273 generation, but allows us to illustrate some important points. First, lets
274 talk about code generation for prototypes: they are used both for function
275 bodies and external function declarations. The code starts with:</p>
278 <pre>
279 let codegen_proto = function
280 | Ast.Prototype (name, args) ->
281 (* Make the function type: double(double,double) etc. *)
282 let doubles = Array.make (Array.length args) double_type in
283 let ft = function_type double_type doubles in
284 let f =
285 match lookup_function name the_module with
286 </pre>
287 </div>
289 <p>This code packs a lot of power into a few lines. Note first that this
292 really talks about the external interface for a function (not the value computed
293 by an expression), it makes sense for it to return the LLVM Function it
294 corresponds to when codegen'd.</p>
297 that should be used for a given Prototype. Since all function arguments in
298 Kaleidoscope are of type double, the first line creates a vector of "N" LLVM
300 function type that takes "N" doubles as arguments, returns one double as a
301 result, and that is not vararg (that uses the function
305 <p>The final line above checks if the function has already been defined in
309 <pre>
310 | None -> declare_function name ft the_module
311 </pre>
312 </div>
314 <p>This indicates the type and name to use, as well as which module to insert
315 into. By default we assume a function has
317 linkage</a>" means that the function may be defined outside the current module
318 and/or that it is callable by functions outside the module. The "<tt>name</tt>"
319 passed in is the name the user specified: this name is registered in
320 "<tt>Codegen.the_module</tt>"s symbol table, which is used by the function call
321 code above.</p>
323 <p>In Kaleidoscope, I choose to allow redefinitions of functions in two cases:
324 first, we want to allow 'extern'ing a function more than once, as long as the
325 prototypes for the externs match (since all arguments have the same type, we
326 just have to check that the number of arguments match). Second, we want to
327 allow 'extern'ing a function and then defining a body for it. This is useful
328 when defining mutually recursive functions.</p>
331 <pre>
332 (* If 'f' conflicted, there was already something named 'name'. If it
333 * has a body, don't allow redefinition or reextern. *)
334 | Some f ->
335 (* If 'f' already has a body, reject this. *)
336 if Array.length (basic_blocks f) == 0 then () else
337 raise (Error "redefinition of function");
339 (* If 'f' took a different number of arguments, reject. *)
340 if Array.length (params f) == Array.length args then () else
341 raise (Error "redefinition of function with different # args");
342 f
343 in
344 </pre>
345 </div>
347 <p>In order to verify the logic above, we first check to see if the pre-existing
348 function is "empty". In this case, empty means that it has no basic blocks in
349 it, which means it has no body. If it has no body, it is a forward
350 declaration. Since we don't allow anything after a full definition of the
351 function, the code rejects this case. If the previous reference to a function
352 was an 'extern', we simply verify that the number of arguments for that
353 definition and this one match up. If not, we emit an error.</p>
356 <pre>
357 (* Set names for all arguments. *)
358 Array.iteri (fun i a ->
359 let n = args.(i) in
360 set_value_name n a;
361 Hashtbl.add named_values n a;
362 ) (params f);
363 f
364 </pre>
365 </div>
367 <p>The last bit of code for prototypes loops over all of the arguments in the
368 function, setting the name of the LLVM Argument objects to match, and registering
371 object to the caller. Note that we don't check for conflicting
372 argument names here (e.g. "extern foo(a b a)"). Doing so would be very
373 straight-forward with the mechanics we have already used above.</p>
376 <pre>
377 let codegen_func = function
378 | Ast.Function (proto, body) ->
379 Hashtbl.clear named_values;
380 let the_function = codegen_proto proto in
381 </pre>
382 </div>
384 <p>Code generation for function definitions starts out simply enough: we just
385 codegen the prototype (Proto) and verify that it is ok. We then clear out the
387 from the last function we compiled. Code generation of the prototype ensures
388 that there is an LLVM Function object that is ready to go for us.</p>
391 <pre>
392 (* Create a new basic block to start insertion into. *)
393 let bb = append_block context "entry" the_function in
394 position_at_end bb builder;
396 try
397 let ret_val = codegen_expr body in
398 </pre>
399 </div>
402 first line creates a new
405 tells the builder that new instructions should be inserted into the end of the
406 new basic block. Basic blocks in LLVM are an important part of functions that
407 define the <a
409 Since we don't have any control flow, our functions will only contain one
414 <pre>
415 let ret_val = codegen_expr body in
417 (* Finish off the function. *)
418 let _ = build_ret ret_val builder in
420 (* Validate the generated code, checking for consistency. *)
421 Llvm_analysis.assert_valid_function the_function;
423 the_function
424 </pre>
425 </div>
428 method for the root expression of the function. If no error happens, this emits
429 code to compute the expression into the entry block and returns the value that
430 was computed. Assuming no error, we then create an LLVM <a
432 Once the function is built, we call
434 function does a variety of consistency checks on the generated code, to
435 determine if our compiler is doing everything right. Using this is important:
436 it can catch a lot of bugs. Once the function is finished and validated, we
437 return it.</p>
440 <pre>
441 with e ->
442 delete_function the_function;
443 raise e
444 </pre>
445 </div>
447 <p>The only piece left here is handling of the error case. For simplicity, we
448 handle this by merely deleting the function we produced with the
450 function that they incorrectly typed in before: if we didn't delete it, it
451 would live in the symbol table, with a body, preventing future redefinition.</p>
454 can return a previously defined forward declaration, our code can actually delete
455 a forward declaration. There are a number of ways to fix this bug, see what you
456 can come up with! Here is a testcase:</p>
459 <pre>
460 extern foo(a b); # ok, defines foo.
461 def foo(a b) c; # error, 'c' is invalid.
463 </pre>
464 </div>
466 </div>
468 <!-- *********************************************************************** -->
470 Closing Thoughts</a></div>
471 <!-- *********************************************************************** -->
475 <p>
476 For now, code generation to LLVM doesn't really get us much, except that we can
477 look at the pretty IR calls. The sample code inserts calls to Codegen into the
478 "<tt>Toplevel.main_loop</tt>", and then dumps out the LLVM IR. This gives a
479 nice way to look at the LLVM IR for simple functions. For example:
480 </p>
483 <pre>
485 Read top-level expression:
486 define double @""() {
487 entry:
489 ret double %addtmp
490 }
491 </pre>
492 </div>
494 <p>Note how the parser turns the top-level expression into anonymous functions
496 support</a> in the next chapter. Also note that the code is very literally
497 transcribed, no optimizations are being performed. We will
499 in the next chapter.</p>
502 <pre>
504 Read function definition:
505 define double @foo(double %a, double %b) {
506 entry:
507 %multmp = fmul double %a, %a
508 %multmp1 = fmul double 2.000000e+00, %a
509 %multmp2 = fmul double %multmp1, %b
510 %addtmp = fadd double %multmp, %multmp2
511 %multmp3 = fmul double %b, %b
512 %addtmp4 = fadd double %addtmp, %multmp3
513 ret double %addtmp4
514 }
515 </pre>
516 </div>
518 <p>This shows some simple arithmetic. Notice the striking similarity to the
519 LLVM builder calls that we use to create the instructions.</p>
522 <pre>
524 Read function definition:
525 define double @bar(double %a) {
526 entry:
527 %calltmp = call double @foo(double %a, double 4.000000e+00)
528 %calltmp1 = call double @bar(double 3.133700e+04)
529 %addtmp = fadd double %calltmp, %calltmp1
530 ret double %addtmp
531 }
532 </pre>
533 </div>
535 <p>This shows some function calls. Note that this function will take a long
536 time to execute if you call it. In the future we'll add conditional control
537 flow to actually make recursion useful :).</p>
540 <pre>
542 Read extern:
543 declare double @cos(double)
546 Read top-level expression:
547 define double @""() {
548 entry:
549 %calltmp = call double @cos(double 1.234000e+00)
550 ret double %calltmp
551 }
552 </pre>
553 </div>
559 <pre>
561 ; ModuleID = 'my cool jit'
563 define double @""() {
564 entry:
566 ret double %addtmp
567 }
569 define double @foo(double %a, double %b) {
570 entry:
571 %multmp = fmul double %a, %a
572 %multmp1 = fmul double 2.000000e+00, %a
573 %multmp2 = fmul double %multmp1, %b
574 %addtmp = fadd double %multmp, %multmp2
575 %multmp3 = fmul double %b, %b
576 %addtmp4 = fadd double %addtmp, %multmp3
577 ret double %addtmp4
578 }
580 define double @bar(double %a) {
581 entry:
582 %calltmp = call double @foo(double %a, double 4.000000e+00)
583 %calltmp1 = call double @bar(double 3.133700e+04)
584 %addtmp = fadd double %calltmp, %calltmp1
585 ret double %addtmp
586 }
588 declare double @cos(double)
590 define double @""() {
591 entry:
592 %calltmp = call double @cos(double 1.234000e+00)
593 ret double %calltmp
594 }
595 </pre>
596 </div>
598 <p>When you quit the current demo, it dumps out the IR for the entire module
599 generated. Here you can see the big picture with all the functions referencing
600 each other.</p>
602 <p>This wraps up the third chapter of the Kaleidoscope tutorial. Up next, we'll
606 </div>
609 <!-- *********************************************************************** -->
611 <!-- *********************************************************************** -->
615 <p>
616 Here is the complete code listing for our running example, enhanced with the
617 LLVM code generator. Because this uses the LLVM libraries, we need to link
618 them in. To do this, we use the <a
620 our makefile/command line about which options to use:</p>
623 <pre>
624 # Compile
625 ocamlbuild toy.byte
626 # Run
627 ./toy.byte
628 </pre>
629 </div>
633 <dl>
636 <pre>
639 </pre>
640 </dd>
644 <pre>
645 open Ocamlbuild_plugin;;
647 ocaml_lib ~extern:true "llvm";;
648 ocaml_lib ~extern:true "llvm_analysis";;
651 </pre>
652 </dd>
656 <pre>
657 (*===----------------------------------------------------------------------===
658 * Lexer Tokens
659 *===----------------------------------------------------------------------===*)
661 (* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of
662 * these others for known things. *)
663 type token =
664 (* commands *)
665 | Def | Extern
667 (* primary *)
668 | Ident of string | Number of float
670 (* unknown *)
671 | Kwd of char
672 </pre>
673 </dd>
677 <pre>
678 (*===----------------------------------------------------------------------===
679 * Lexer
680 *===----------------------------------------------------------------------===*)
682 let rec lex = parser
683 (* Skip any whitespace. *)
686 (* identifier: [a-zA-Z][a-zA-Z0-9] *)
688 let buffer = Buffer.create 1 in
689 Buffer.add_char buffer c;
690 lex_ident buffer stream
694 let buffer = Buffer.create 1 in
695 Buffer.add_char buffer c;
696 lex_number buffer stream
698 (* Comment until end of line. *)
700 lex_comment stream
702 (* Otherwise, just return the character as its ascii value. *)
706 (* end of stream. *)
709 and lex_number buffer = parser
711 Buffer.add_char buffer c;
712 lex_number buffer stream
716 and lex_ident buffer = parser
718 Buffer.add_char buffer c;
719 lex_ident buffer stream
721 match Buffer.contents buffer with
726 and lex_comment = parser
730 </pre>
731 </dd>
735 <pre>
736 (*===----------------------------------------------------------------------===
737 * Abstract Syntax Tree (aka Parse Tree)
738 *===----------------------------------------------------------------------===*)
740 (* expr - Base type for all expression nodes. *)
741 type expr =
742 (* variant for numeric literals like "1.0". *)
743 | Number of float
745 (* variant for referencing a variable, like "a". *)
746 | Variable of string
748 (* variant for a binary operator. *)
749 | Binary of char * expr * expr
751 (* variant for function calls. *)
752 | Call of string * expr array
754 (* proto - This type represents the "prototype" for a function, which captures
755 * its name, and its argument names (thus implicitly the number of arguments the
756 * function takes). *)
757 type proto = Prototype of string * string array
759 (* func - This type represents a function definition itself. *)
760 type func = Function of proto * expr
761 </pre>
762 </dd>
766 <pre>
767 (*===---------------------------------------------------------------------===
768 * Parser
769 *===---------------------------------------------------------------------===*)
771 (* binop_precedence - This holds the precedence for each binary operator that is
772 * defined *)
773 let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
775 (* precedence - Get the precedence of the pending binary operator token. *)
778 (* primary
779 * ::= identifier
780 * ::= numberexpr
781 * ::= parenexpr *)
782 let rec parse_primary = parser
783 (* numberexpr ::= number *)
786 (* parenexpr ::= '(' expression ')' *)
789 (* identifierexpr
790 * ::= identifier
791 * ::= identifier '(' argumentexpr ')' *)
793 let rec parse_args accumulator = parser
795 begin parser
798 end stream
800 in
801 let rec parse_ident id = parser
802 (* Call. *)
803 | [< 'Token.Kwd '(';
804 args=parse_args [];
806 Ast.Call (id, Array.of_list (List.rev args))
808 (* Simple variable ref. *)
810 in
811 parse_ident id stream
815 (* binoprhs
816 * ::= ('+' primary)* *)
817 and parse_bin_rhs expr_prec lhs stream =
818 match Stream.peek stream with
819 (* If this is a binop, find its precedence. *)
820 | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
821 let token_prec = precedence c in
823 (* If this is a binop that binds at least as tightly as the current binop,
824 * consume it, otherwise we are done. *)
825 if token_prec < expr_prec then lhs else begin
826 (* Eat the binop. *)
827 Stream.junk stream;
829 (* Parse the primary expression after the binary operator. *)
830 let rhs = parse_primary stream in
832 (* Okay, we know this is a binop. *)
833 let rhs =
834 match Stream.peek stream with
835 | Some (Token.Kwd c2) ->
836 (* If BinOp binds less tightly with rhs than the operator after
837 * rhs, let the pending operator take rhs as its lhs. *)
838 let next_prec = precedence c2 in
839 if token_prec < next_prec
840 then parse_bin_rhs (token_prec + 1) rhs stream
841 else rhs
842 | _ -> rhs
843 in
845 (* Merge lhs/rhs. *)
846 let lhs = Ast.Binary (c, lhs, rhs) in
847 parse_bin_rhs expr_prec lhs stream
848 end
849 | _ -> lhs
851 (* expression
852 * ::= primary binoprhs *)
853 and parse_expr = parser
856 (* prototype
857 * ::= id '(' id* ')' *)
858 let parse_prototype =
859 let rec parse_args accumulator = parser
862 in
864 parser
865 | [< 'Token.Ident id;
866 'Token.Kwd '(' ?? "expected '(' in prototype";
867 args=parse_args [];
869 (* success. *)
870 Ast.Prototype (id, Array.of_list (List.rev args))
873 raise (Stream.Error "expected function name in prototype")
875 (* definition ::= 'def' prototype expression *)
876 let parse_definition = parser
878 Ast.Function (p, e)
880 (* toplevelexpr ::= expression *)
881 let parse_toplevel = parser
883 (* Make an anonymous proto. *)
884 Ast.Function (Ast.Prototype ("", [||]), e)
886 (* external ::= 'extern' prototype *)
887 let parse_extern = parser
889 </pre>
890 </dd>
894 <pre>
895 (*===----------------------------------------------------------------------===
896 * Code Generation
897 *===----------------------------------------------------------------------===*)
899 open Llvm
901 exception Error of string
903 let context = global_context ()
904 let the_module = create_module context "my cool jit"
905 let builder = builder context
906 let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
907 let double_type = double_type context
909 let rec codegen_expr = function
910 | Ast.Number n -> const_float double_type n
911 | Ast.Variable name ->
912 (try Hashtbl.find named_values name with
914 | Ast.Binary (op, lhs, rhs) ->
915 let lhs_val = codegen_expr lhs in
916 let rhs_val = codegen_expr rhs in
917 begin
918 match op with
924 let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
925 build_uitofp i double_type "booltmp" builder
927 end
928 | Ast.Call (callee, args) ->
929 (* Look up the name in the module table. *)
930 let callee =
931 match lookup_function callee the_module with
932 | Some callee -> callee
934 in
935 let params = params callee in
937 (* If argument mismatch error. *)
938 if Array.length params == Array.length args then () else
939 raise (Error "incorrect # arguments passed");
940 let args = Array.map codegen_expr args in
941 build_call callee args "calltmp" builder
943 let codegen_proto = function
944 | Ast.Prototype (name, args) ->
945 (* Make the function type: double(double,double) etc. *)
946 let doubles = Array.make (Array.length args) double_type in
947 let ft = function_type double_type doubles in
948 let f =
949 match lookup_function name the_module with
950 | None -> declare_function name ft the_module
952 (* If 'f' conflicted, there was already something named 'name'. If it
953 * has a body, don't allow redefinition or reextern. *)
954 | Some f ->
955 (* If 'f' already has a body, reject this. *)
956 if block_begin f <> At_end f then
957 raise (Error "redefinition of function");
959 (* If 'f' took a different number of arguments, reject. *)
960 if element_type (type_of f) <> ft then
961 raise (Error "redefinition of function with different # args");
962 f
963 in
965 (* Set names for all arguments. *)
966 Array.iteri (fun i a ->
967 let n = args.(i) in
968 set_value_name n a;
969 Hashtbl.add named_values n a;
970 ) (params f);
971 f
973 let codegen_func = function
974 | Ast.Function (proto, body) ->
975 Hashtbl.clear named_values;
976 let the_function = codegen_proto proto in
978 (* Create a new basic block to start insertion into. *)
979 let bb = append_block context "entry" the_function in
980 position_at_end bb builder;
982 try
983 let ret_val = codegen_expr body in
985 (* Finish off the function. *)
986 let _ = build_ret ret_val builder in
988 (* Validate the generated code, checking for consistency. *)
989 Llvm_analysis.assert_valid_function the_function;
991 the_function
992 with e ->
993 delete_function the_function;
994 raise e
995 </pre>
996 </dd>
1000 <pre>
1001 (*===----------------------------------------------------------------------===
1002 * Top-Level parsing and JIT Driver
1003 *===----------------------------------------------------------------------===*)
1005 open Llvm
1007 (* top ::= definition | external | expression | ';' *)
1008 let rec main_loop stream =
1009 match Stream.peek stream with
1010 | None -> ()
1012 (* ignore top-level semicolons. *)
1013 | Some (Token.Kwd ';') ->
1014 Stream.junk stream;
1015 main_loop stream
1017 | Some token ->
1018 begin
1019 try match token with
1020 | Token.Def ->
1021 let e = Parser.parse_definition stream in
1022 print_endline "parsed a function definition.";
1023 dump_value (Codegen.codegen_func e);
1024 | Token.Extern ->
1025 let e = Parser.parse_extern stream in
1026 print_endline "parsed an extern.";
1027 dump_value (Codegen.codegen_proto e);
1028 | _ ->
1029 (* Evaluate a top-level expression into an anonymous function. *)
1030 let e = Parser.parse_toplevel stream in
1031 print_endline "parsed a top-level expr";
1032 dump_value (Codegen.codegen_func e);
1033 with Stream.Error s | Codegen.Error s ->
1034 (* Skip token for error recovery. *)
1035 Stream.junk stream;
1036 print_endline s;
1037 end;
1038 print_string "ready> "; flush stdout;
1039 main_loop stream
1040 </pre>
1041 </dd>
1045 <pre>
1046 (*===----------------------------------------------------------------------===
1047 * Main driver code.
1048 *===----------------------------------------------------------------------===*)
1050 open Llvm
1052 let main () =
1053 (* Install standard binary operators.
1054 * 1 is the lowest precedence. *)
1056 Hashtbl.add Parser.binop_precedence '+' 20;
1057 Hashtbl.add Parser.binop_precedence '-' 20;
1058 Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *)
1060 (* Prime the first token. *)
1061 print_string "ready> "; flush stdout;
1062 let stream = Lexer.lex (Stream.of_channel stdin) in
1064 (* Run the main "interpreter loop" now. *)
1065 Toplevel.main_loop stream;
1067 (* Print out all the generated code. *)
1068 dump_module Codegen.the_module
1069 ;;
1071 main ()
1072 </pre>
1073 </dd>
1074 </dl>
1077 </div>
1079 <!-- *********************************************************************** -->
1080 <hr>
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1090 Last modified: $Date$
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