6 public class Parser extends Lexer {
8 public static void main(String[] s) throws Exception {
9 Parser p = new Parser(new InputStreamReader(System.in));
11 Expr block = p.parseBlock(false);
12 if (block == null) return;
13 System.out.println(block);
14 if (p.peekToken() == -1) return;
18 public Parser(Reader r) throws IOException { super(r); }
19 private Parser skipToken() throws IOException { getToken(); return this; }
21 /** sorta like gcc trees */
22 public static class Expr {
29 Expr next = null; // if this expr is part of a list
34 public String toString() { return toString(0); }
36 public String toString(int indent) {
38 for(int i=0; i<indent; i++) ret += " ";
39 ret += codeToString[code];
40 if (code == NUMBER) ret += " " + number;
41 else if (string != null) ret += " \"" + string + "\"";
43 if (left != null) ret += left.toString(indent + 2);
44 if (right != null) ret += right.toString(indent + 2);
45 if (extra != null) ret += extra.toString(indent + 2);
46 if (next != null) ret += next.toString(indent);
51 public Expr(String s) { code = STRING; this.string = s; } // an identifier or label
52 public Expr(Number n) { code = NUMBER; this.number = n; } // an identifier or label
53 public Expr(int code) { this(code, null, null, null); }
54 public Expr(int code, String s) { this.code = code; string = s; }
55 public Expr(int code, Expr left) { this(code, left, null, null); }
56 public Expr(int code, Expr left, Expr right) { this(code, left, right, null); }
57 public Expr(int code, Expr left, Expr right, Expr extra) { this.left = left; this.right = right; this.extra = extra; this.code = code; }
60 /** a block is either a single statement or a list of statements surrounded by curly braces; all expressions are also statements */
61 public Expr parseBlock(boolean requireBraces) throws IOException {
63 int tok = peekToken();
64 boolean braced = tok == LC;
65 if (requireBraces && !braced) throw new Error("expected {");
66 if (braced) skipToken();
71 switch(tok = peekToken()) {
73 case LC: smt = parseBlock(true); break;
74 case THROW: case RETURN: case ASSERT:
75 smt = new Expr(tok, skipToken().parseExpr());
76 if (getToken() != SEMI) throw new Error("expected ;");
78 case GOTO: case BREAK: case CONTINUE:
80 if (getToken() == NAME)
81 smt = new Expr(tok, new Expr(string));
83 throw new Error("goto must be followed by a label");
86 if (getToken() != SEMI) throw new Error("expected ;");
90 if (braced) skipToken();
95 if (!braced) break OUTER;
101 if (head == null) throw new Error("empty statement list");
106 if (head == null) head = tail = smt; else tail = (tail.next = smt);
108 return new Expr(LC, head);
111 static byte[] precedence = new byte[MAX_TOKEN + 1];
113 precedence[COMMA] = 1;
114 precedence[ASSIGN] = 2;
115 precedence[GT] = precedence[GE] = 3;
116 precedence[OR] = precedence[AND] = 4;
117 precedence[BITOR] = 5;
118 precedence[BITXOR] = 6;
119 precedence[BITAND] = 7;
120 precedence[EQ] = precedence[NE] = 8;
121 precedence[LT] = precedence[LE] = 9;
122 precedence[SHEQ] = precedence[SHNE] = 10;
123 precedence[LSH] = precedence[RSH] = precedence[URSH] = 11;
124 precedence[ADD] = precedence[SUB] = 12;
125 precedence[MUL] = precedence[DIV] = precedence[MOD] = 13;
126 precedence[BITNOT] = precedence[INSTANCEOF] = 14;
127 precedence[INC] = precedence[DEC] = 15;
129 precedence[DOT] = 17;
132 // called after each parseExpr(); returns null if we can't make the expression any bigger
133 public Expr parseExpr() throws IOException { return parseExpr_(null, 0); }
134 public Expr parseExpr(Expr prefix, int minPrecedence) throws IOException {
138 if (peekToken() == -1) break;
139 prefix = parseExpr_(prefix, minPrecedence);
140 if (prefix == null) throw new Error("parseExpr_() returned null");
141 } while (save != prefix);
145 public Expr parseExpr_(Expr prefix, int minPrecedence) throws IOException {
152 int tok = getToken();
154 if (minPrecedence != -1 && minPrecedence != 0 && tok < precedence.length && precedence[tok] != 0 && precedence[tok] <= minPrecedence) {
159 // these case arms match the precedence of operators; each arm is a precedence level.
162 case COMMA: case ASSIGN: case GT: case GE: case OR: case AND:
163 case BITOR: case BITXOR: case BITAND: case EQ: case NE: case LT:
164 case LE: case SHEQ: case SHNE: case LSH: case RSH: case URSH:
165 case ADD: case SUB: case MUL: case DIV: case MOD: case DOT:
166 return new Expr(tok, prefix, parseExpr(null, precedence[tok]));
168 case BITNOT: case INSTANCEOF:
169 return new Expr(tok, parseExpr(null, precedence[tok]));
171 // FIXME: this isn't 100% right
173 return new Expr(tok, prefix, (tok == INC || tok == DEC) ? null : parseExpr());
176 if (prefix == null) {
178 Expr r = parseExpr(null, -1);
179 if ((tok = getToken()) != RP) throw new Error("expected ), got " + codeToString[tok]);
184 while(peekToken() != RP) {
185 Expr e = parseExpr(null, precedence[COMMA]);
186 if (head == null) head = tail = e; else tail = tail.next = e;
188 if (tok == RP) { pushBackToken(); break; }
189 if (tok != COMMA) throw new Error("expected comma or right paren, got " + codeToString[tok]);
192 return new Expr(LP, prefix, head);
196 if (prefix != null) {
199 if (getToken() != RB) throw new Error("expected a right brace");
200 return new Expr(LB, prefix, e1);
205 if (tok == RB) return new Expr(LB, prefix, head);
206 if (head == null) head = tail = parseExpr(); else tail = tail.next = parseExpr();
208 if (tok != COMMA && tok != RP) throw new Error("expected right bracket or comma");
213 if (prefix != null) throw new Error("didn't expect non-null prefix");
216 if (tok == RC) return new Expr(LC, head);
217 if (tok != NAME) throw new Error("expecting name");
218 Expr name = parseExpr();
219 if (tok != COLON) throw new Error("expecting colon");
220 e1 = new Expr(COLON, name, parseExpr());
221 if (head == null) head = tail = e1; else tail = tail.next = e1;
223 if (tok != COMMA && tok != RP) throw new Error("expected right curly or comma");
228 if (getToken() != COLON) throw new Error("expected colon to close ?: expression");
230 return new Expr(HOOK, prefix, e2, e3);
233 if (prefix != null) throw new Error("didn't expect non-null prefix");
234 if (getToken() != LP) throw new Error("expected left paren");
235 Expr switchExpr = parseExpr();
236 if (getToken() != RP) throw new Error("expected left paren");
237 if (getToken() != LC) throw new Error("expected left brace");
238 Expr firstExpr = null;
239 Expr lastExpr = null;
241 if (getToken() != CASE) throw new Error("expected CASE");
242 Expr caseExpr = parseExpr();
243 if (getToken() != COLON) throw new Error("expected COLON");
244 Expr e = new Expr(CASE, caseExpr, parseBlock(false));
245 if (lastExpr == null) firstExpr = e;
246 else lastExpr.next = e;
248 if (getToken() == RC) return new Expr(SWITCH, switchExpr, firstExpr);
253 if (prefix != null) throw new Error("didn't expect non-null prefix");
254 if (getToken() != LP) throw new Error("function keyword must be followed by a left paren");
255 Expr formalArgs = null, cur = null;
258 if (tok != NAME) throw new Error("expected a variable name");
259 if (cur == null) { formalArgs = cur = new Expr(string); }
260 else { cur.next = new Expr(NAME, string); cur = cur.next; }
262 if (tok == RP) break;
263 if (tok != COMMA) throw new Error("function argument list must consist of alternating NAMEs and COMMAs");
266 return new Expr(FUNCTION, formalArgs, parseBlock(true));
270 return new Expr(string);
273 return new Expr(number);
276 if (prefix != null) throw new Error("didn't expect non-null prefix");
278 if (getToken() != NAME) throw new Error("variable declarations must start with a variable name");
279 Expr name = new Expr(NAME, string);
285 initVal = parseExpr();
287 e = new Expr(ASSIGN, name, initVal);
289 e = new Expr(NAME, name);
291 if (head == null) head = tail = e; else tail = tail.next = e;
292 if (tok != COMMA) break;
295 return new Expr(VAR, head);
298 return new Expr(NULL);
301 if (prefix != null) { pushBackToken(); return prefix; }
302 return parseExpr(new Expr(NAME, string), minPrecedence);
304 case TRUE: case FALSE: case NOP:
305 if (prefix != null) throw new Error("didn't expect non-null prefix");
306 return new Expr(tok);
309 // FIXME: we deliberately allow you to omit braces in catch{}/finally{} if they are single statements...
310 if (prefix != null) throw new Error("didn't expect non-null prefix");
311 Expr tryBlock = parseBlock(true);
312 while ((tok = peekToken()) == CATCH) {
314 if (getToken() != LP) throw new Error("expected (");
315 if (getToken() != NAME) throw new Error("expected name");
316 // FIXME: record the name
317 if (getToken() != RP) throw new Error("expected )");
318 if (head == null) head = tail = parseBlock(false);
319 else tail = tail.next = parseBlock(false);
321 if (head == null) throw new Error("try without catch");
322 return new Expr(TRY, tryBlock, head, tok == FINALLY ? skipToken().parseBlock(false) : null);
325 // FIXME: a.b=c becomes PUT(a,b,c) not ASSIGN(DOT(a,b),c)
327 case IF: case WHILE: {
328 if (prefix != null) throw new Error("didn't expect non-null prefix");
329 if (getToken() != LP) throw new Error("expected left paren");
330 Expr parenExpr = parseExpr(null, -1);
332 if ((t = getToken()) != RP) throw new Error("expected right paren, but got " + codeToString[t]);
333 Expr firstBlock = parseBlock(false);
334 if (tok == IF && peekToken() == ELSE)
335 return new Expr(tok, parenExpr, firstBlock, skipToken().parseBlock(false));
336 return new Expr(tok, parenExpr, firstBlock);
341 if (prefix != null) throw new Error("didn't expect non-null prefix");
342 if (getToken() != LP) throw new Error("expected left paren");
343 e1 = parseExpr(null, -1);
344 if (getToken() != SEMI) throw new Error("expected ;");
345 e2 = parseExpr(null, -1);
346 if (getToken() != SEMI) throw new Error("expected ;");
347 e3 = parseExpr(null, -1); // FIXME: this guy has to be okay with ending via a )
348 if (getToken() != RP) throw new Error("expected right paren");
349 throw new Error("not yet implemented");
350 //return new Expr(FOR, e1, e2, e3, parseBlock(false));
353 if (prefix != null) throw new Error("didn't expect non-null prefix");
354 Expr firstBlock = parseBlock(false);
355 if (getToken() != WHILE) throw new Error("expecting WHILE");
356 if (getToken() != LP) throw new Error("expected left paren");
357 Expr whileExpr = parseExpr();
358 if (getToken() != RP) throw new Error("expected right paren");
359 if (getToken() != SEMI) throw new Error("semicolon");
360 return new Expr(DO, firstBlock, whileExpr);
363 case VOID: case RESERVED:
364 throw new Error("reserved word that you shouldn't be using");
367 throw new Error("WITH not yet implemented"); // FIXME