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