1 #include <cctype>
2 #include <cstdio>
3 #include <cstdlib>
4 #include <map>
5 #include <memory>
6 #include <string>
7 #include <utility>
8 #include <vector>
9 
10 //===----------------------------------------------------------------------===//
11 // Lexer
12 //===----------------------------------------------------------------------===//
13 
14 // The lexer returns tokens [0-255] if it is an unknown character, otherwise one
15 // of these for known things.
16 enum Token {
17   tok_eof = -1,
18 
19   // commands
20   tok_def = -2,
21   tok_extern = -3,
22 
23   // primary
24   tok_identifier = -4,
25   tok_number = -5
26 };
27 
28 static std::string IdentifierStr; // Filled in if tok_identifier
29 static double NumVal;             // Filled in if tok_number
30 
31 /// gettok - Return the next token from standard input.
32 static int gettok() {
33   static int LastChar = ' ';
34 
35   // Skip any whitespace.
36   while (isspace(LastChar))
37     LastChar = getchar();
38 
39   if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
40     IdentifierStr = LastChar;
41     while (isalnum((LastChar = getchar())))
42       IdentifierStr += LastChar;
43 
44     if (IdentifierStr == "def")
45       return tok_def;
46     if (IdentifierStr == "extern")
47       return tok_extern;
48     return tok_identifier;
49   }
50 
51   if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
52     std::string NumStr;
53     do {
54       NumStr += LastChar;
55       LastChar = getchar();
56     } while (isdigit(LastChar) || LastChar == '.');
57 
58     NumVal = strtod(NumStr.c_str(), nullptr);
59     return tok_number;
60   }
61 
62   if (LastChar == '#') {
63     // Comment until end of line.
64     do
65       LastChar = getchar();
66     while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
67 
68     if (LastChar != EOF)
69       return gettok();
70   }
71 
72   // Check for end of file.  Don't eat the EOF.
73   if (LastChar == EOF)
74     return tok_eof;
75 
76   // Otherwise, just return the character as its ascii value.
77   int ThisChar = LastChar;
78   LastChar = getchar();
79   return ThisChar;
80 }
81 
82 //===----------------------------------------------------------------------===//
83 // Abstract Syntax Tree (aka Parse Tree)
84 //===----------------------------------------------------------------------===//
85 
86 namespace {
87 
88 /// ExprAST - Base class for all expression nodes.
89 class ExprAST {
90 public:
91   virtual ~ExprAST() = default;
92 };
93 
94 /// NumberExprAST - Expression class for numeric literals like "1.0".
95 class NumberExprAST : public ExprAST {
96   double Val;
97 
98 public:
99   NumberExprAST(double Val) : Val(Val) {}
100 };
101 
102 /// VariableExprAST - Expression class for referencing a variable, like "a".
103 class VariableExprAST : public ExprAST {
104   std::string Name;
105 
106 public:
107   VariableExprAST(const std::string &Name) : Name(Name) {}
108 };
109 
110 /// BinaryExprAST - Expression class for a binary operator.
111 class BinaryExprAST : public ExprAST {
112   char Op;
113   std::unique_ptr<ExprAST> LHS, RHS;
114 
115 public:
116   BinaryExprAST(char Op, std::unique_ptr<ExprAST> LHS,
117                 std::unique_ptr<ExprAST> RHS)
118       : Op(Op), LHS(std::move(LHS)), RHS(std::move(RHS)) {}
119 };
120 
121 /// CallExprAST - Expression class for function calls.
122 class CallExprAST : public ExprAST {
123   std::string Callee;
124   std::vector<std::unique_ptr<ExprAST>> Args;
125 
126 public:
127   CallExprAST(const std::string &Callee,
128               std::vector<std::unique_ptr<ExprAST>> Args)
129       : Callee(Callee), Args(std::move(Args)) {}
130 };
131 
132 /// PrototypeAST - This class represents the "prototype" for a function,
133 /// which captures its name, and its argument names (thus implicitly the number
134 /// of arguments the function takes).
135 class PrototypeAST {
136   std::string Name;
137   std::vector<std::string> Args;
138 
139 public:
140   PrototypeAST(const std::string &Name, std::vector<std::string> Args)
141       : Name(Name), Args(std::move(Args)) {}
142 
143   const std::string &getName() const { return Name; }
144 };
145 
146 /// FunctionAST - This class represents a function definition itself.
147 class FunctionAST {
148   std::unique_ptr<PrototypeAST> Proto;
149   std::unique_ptr<ExprAST> Body;
150 
151 public:
152   FunctionAST(std::unique_ptr<PrototypeAST> Proto,
153               std::unique_ptr<ExprAST> Body)
154       : Proto(std::move(Proto)), Body(std::move(Body)) {}
155 };
156 
157 } // end anonymous namespace
158 
159 //===----------------------------------------------------------------------===//
160 // Parser
161 //===----------------------------------------------------------------------===//
162 
163 /// CurTok/getNextToken - Provide a simple token buffer.  CurTok is the current
164 /// token the parser is looking at.  getNextToken reads another token from the
165 /// lexer and updates CurTok with its results.
166 static int CurTok;
167 static int getNextToken() { return CurTok = gettok(); }
168 
169 /// BinopPrecedence - This holds the precedence for each binary operator that is
170 /// defined.
171 static std::map<char, int> BinopPrecedence;
172 
173 /// GetTokPrecedence - Get the precedence of the pending binary operator token.
174 static int GetTokPrecedence() {
175   if (!isascii(CurTok))
176     return -1;
177 
178   // Make sure it's a declared binop.
179   int TokPrec = BinopPrecedence[CurTok];
180   if (TokPrec <= 0)
181     return -1;
182   return TokPrec;
183 }
184 
185 /// LogError* - These are little helper functions for error handling.
186 std::unique_ptr<ExprAST> LogError(const char *Str) {
187   fprintf(stderr, "Error: %s\n", Str);
188   return nullptr;
189 }
190 std::unique_ptr<PrototypeAST> LogErrorP(const char *Str) {
191   LogError(Str);
192   return nullptr;
193 }
194 
195 static std::unique_ptr<ExprAST> ParseExpression();
196 
197 /// numberexpr ::= number
198 static std::unique_ptr<ExprAST> ParseNumberExpr() {
199   auto Result = std::make_unique<NumberExprAST>(NumVal);
200   getNextToken(); // consume the number
201   return std::move(Result);
202 }
203 
204 /// parenexpr ::= '(' expression ')'
205 static std::unique_ptr<ExprAST> ParseParenExpr() {
206   getNextToken(); // eat (.
207   auto V = ParseExpression();
208   if (!V)
209     return nullptr;
210 
211   if (CurTok != ')')
212     return LogError("expected ')'");
213   getNextToken(); // eat ).
214   return V;
215 }
216 
217 /// identifierexpr
218 ///   ::= identifier
219 ///   ::= identifier '(' expression* ')'
220 static std::unique_ptr<ExprAST> ParseIdentifierExpr() {
221   std::string IdName = IdentifierStr;
222 
223   getNextToken(); // eat identifier.
224 
225   if (CurTok != '(') // Simple variable ref.
226     return std::make_unique<VariableExprAST>(IdName);
227 
228   // Call.
229   getNextToken(); // eat (
230   std::vector<std::unique_ptr<ExprAST>> Args;
231   if (CurTok != ')') {
232     while (true) {
233       if (auto Arg = ParseExpression())
234         Args.push_back(std::move(Arg));
235       else
236         return nullptr;
237 
238       if (CurTok == ')')
239         break;
240 
241       if (CurTok != ',')
242         return LogError("Expected ')' or ',' in argument list");
243       getNextToken();
244     }
245   }
246 
247   // Eat the ')'.
248   getNextToken();
249 
250   return std::make_unique<CallExprAST>(IdName, std::move(Args));
251 }
252 
253 /// primary
254 ///   ::= identifierexpr
255 ///   ::= numberexpr
256 ///   ::= parenexpr
257 static std::unique_ptr<ExprAST> ParsePrimary() {
258   switch (CurTok) {
259   default:
260     return LogError("unknown token when expecting an expression");
261   case tok_identifier:
262     return ParseIdentifierExpr();
263   case tok_number:
264     return ParseNumberExpr();
265   case '(':
266     return ParseParenExpr();
267   }
268 }
269 
270 /// binoprhs
271 ///   ::= ('+' primary)*
272 static std::unique_ptr<ExprAST> ParseBinOpRHS(int ExprPrec,
273                                               std::unique_ptr<ExprAST> LHS) {
274   // If this is a binop, find its precedence.
275   while (true) {
276     int TokPrec = GetTokPrecedence();
277 
278     // If this is a binop that binds at least as tightly as the current binop,
279     // consume it, otherwise we are done.
280     if (TokPrec < ExprPrec)
281       return LHS;
282 
283     // Okay, we know this is a binop.
284     int BinOp = CurTok;
285     getNextToken(); // eat binop
286 
287     // Parse the primary expression after the binary operator.
288     auto RHS = ParsePrimary();
289     if (!RHS)
290       return nullptr;
291 
292     // If BinOp binds less tightly with RHS than the operator after RHS, let
293     // the pending operator take RHS as its LHS.
294     int NextPrec = GetTokPrecedence();
295     if (TokPrec < NextPrec) {
296       RHS = ParseBinOpRHS(TokPrec + 1, std::move(RHS));
297       if (!RHS)
298         return nullptr;
299     }
300 
301     // Merge LHS/RHS.
302     LHS =
303         std::make_unique<BinaryExprAST>(BinOp, std::move(LHS), std::move(RHS));
304   }
305 }
306 
307 /// expression
308 ///   ::= primary binoprhs
309 ///
310 static std::unique_ptr<ExprAST> ParseExpression() {
311   auto LHS = ParsePrimary();
312   if (!LHS)
313     return nullptr;
314 
315   return ParseBinOpRHS(0, std::move(LHS));
316 }
317 
318 /// prototype
319 ///   ::= id '(' id* ')'
320 static std::unique_ptr<PrototypeAST> ParsePrototype() {
321   if (CurTok != tok_identifier)
322     return LogErrorP("Expected function name in prototype");
323 
324   std::string FnName = IdentifierStr;
325   getNextToken();
326 
327   if (CurTok != '(')
328     return LogErrorP("Expected '(' in prototype");
329 
330   std::vector<std::string> ArgNames;
331   while (getNextToken() == tok_identifier)
332     ArgNames.push_back(IdentifierStr);
333   if (CurTok != ')')
334     return LogErrorP("Expected ')' in prototype");
335 
336   // success.
337   getNextToken(); // eat ')'.
338 
339   return std::make_unique<PrototypeAST>(FnName, std::move(ArgNames));
340 }
341 
342 /// definition ::= 'def' prototype expression
343 static std::unique_ptr<FunctionAST> ParseDefinition() {
344   getNextToken(); // eat def.
345   auto Proto = ParsePrototype();
346   if (!Proto)
347     return nullptr;
348 
349   if (auto E = ParseExpression())
350     return std::make_unique<FunctionAST>(std::move(Proto), std::move(E));
351   return nullptr;
352 }
353 
354 /// toplevelexpr ::= expression
355 static std::unique_ptr<FunctionAST> ParseTopLevelExpr() {
356   if (auto E = ParseExpression()) {
357     // Make an anonymous proto.
358     auto Proto = std::make_unique<PrototypeAST>("__anon_expr",
359                                                 std::vector<std::string>());
360     return std::make_unique<FunctionAST>(std::move(Proto), std::move(E));
361   }
362   return nullptr;
363 }
364 
365 /// external ::= 'extern' prototype
366 static std::unique_ptr<PrototypeAST> ParseExtern() {
367   getNextToken(); // eat extern.
368   return ParsePrototype();
369 }
370 
371 //===----------------------------------------------------------------------===//
372 // Top-Level parsing
373 //===----------------------------------------------------------------------===//
374 
375 static void HandleDefinition() {
376   if (ParseDefinition()) {
377     fprintf(stderr, "Parsed a function definition.\n");
378   } else {
379     // Skip token for error recovery.
380     getNextToken();
381   }
382 }
383 
384 static void HandleExtern() {
385   if (ParseExtern()) {
386     fprintf(stderr, "Parsed an extern\n");
387   } else {
388     // Skip token for error recovery.
389     getNextToken();
390   }
391 }
392 
393 static void HandleTopLevelExpression() {
394   // Evaluate a top-level expression into an anonymous function.
395   if (ParseTopLevelExpr()) {
396     fprintf(stderr, "Parsed a top-level expr\n");
397   } else {
398     // Skip token for error recovery.
399     getNextToken();
400   }
401 }
402 
403 /// top ::= definition | external | expression | ';'
404 static void MainLoop() {
405   while (true) {
406     fprintf(stderr, "ready> ");
407     switch (CurTok) {
408     case tok_eof:
409       return;
410     case ';': // ignore top-level semicolons.
411       getNextToken();
412       break;
413     case tok_def:
414       HandleDefinition();
415       break;
416     case tok_extern:
417       HandleExtern();
418       break;
419     default:
420       HandleTopLevelExpression();
421       break;
422     }
423   }
424 }
425 
426 //===----------------------------------------------------------------------===//
427 // Main driver code.
428 //===----------------------------------------------------------------------===//
429 
430 int main() {
431   // Install standard binary operators.
432   // 1 is lowest precedence.
433   BinopPrecedence['<'] = 10;
434   BinopPrecedence['+'] = 20;
435   BinopPrecedence['-'] = 20;
436   BinopPrecedence['*'] = 40; // highest.
437 
438   // Prime the first token.
439   fprintf(stderr, "ready> ");
440   getNextToken();
441 
442   // Run the main "interpreter loop" now.
443   MainLoop();
444 
445   return 0;
446 }
447