龙书附录-一个完整的编译器前端代码

package com.ctgu.parser; import java.io.IOException; import com.ctgu.inter.*; import com.ctgu.lexer.*; import com.ctgu.symbols.*; /* * { int i; int j; float v; float x; float[100] a; while(true) { do i = i+1; while(a[i] < v); do j = j-1; while(a[j] > v); if(i >= j) break; x = a[i]; a[i] = a[j]; a[j] = x; } } * * 语法分析，根据词法单元生成抽象语法树 */ public class Parser { private Lexer lex; //词法分析器 private Token look; //代表当前词法单元 Env top = null; //符号链表顶端 int used = 0; public Parser(Lexer l)throws IOException{ lex = l; move(); } void move()throws IOException{ look = lex.scan(); } void error(String s) { throw new Error("near line "+ lex.line + ": " + s); } //匹配词法单元 void match(int t) throws IOException{ if(look.tag == t) { move(); }else error("syntax error"); } // program -> block public void program() throws IOException{ Stmt s = block(); int begin = s.newlabel(); int after = s.newlabel(); s.emitlabel(begin); s.gen(begin, after); s.emitlabel(after); } // block -> {decls stmts} Stmt block() throws IOException{ match('{'); Env saveEnv = top; top = new Env(top); decls(); Stmt s = stmts(); match('}'); top = saveEnv; return s; } // decls -> decls decl | null; void decls() throws IOException{ while(look.tag == Tag.BASIC){ Type p = type(); Token tok = look; match(Tag.ID); match(';'); Id id = new Id((Word)tok,p,used); top.put(tok, id); used = used + p.width; } } // decl -> type id 数组匹配好像有点问题。。 Type type()throws IOException{ Type p = (Type)look; match(Tag.BASIC); if(look.tag != '[') return p; else return dims(p); } //数组声明匹配 Type dims(Type p)throws IOException{ match('['); Token tok = look; match(Tag.NUM); match(']'); if(look.tag == '[') p = dims(p); return new Array(((Num)tok).value,p); } //匹配语句序列 stmts -> stmts stmt | null Stmt stmts()throws IOException{ if(look.tag == '}') return Stmt.Null; else return new Seq(stmt(),stmts()); } Stmt stmt()throws IOException{ Expr x; Stmt s,s1,s2; Stmt savedStmt; switch(look.tag) { case ';': move(); return Stmt.Null; case Tag.IF: match(Tag.IF); match('('); x = bool(); match(')'); s1 = stmt(); if(look.tag != Tag.ELSE) return new If(x,s1); s2 = stmt(); return new Else(x,s1,s2); case Tag.WHILE: While whilenode = new While(); savedStmt = Stmt.Enclosing; Stmt.Enclosing = whilenode; match(Tag.WHILE); match('('); x = bool(); match(')'); s1 = stmt(); whilenode.init(x, s1); Stmt.Enclosing = savedStmt; return whilenode; case Tag.DO: DoWhile donode = new DoWhile(); savedStmt = Stmt.Enclosing; Stmt.Enclosing = donode; match(Tag.DO); s1 = stmt(); match(Tag.WHILE); match('('); x = bool(); match(')'); match(';'); donode.init(s1, x); Stmt.Enclosing = savedStmt; return donode; case Tag.BREAK: match(Tag.BREAK); match(';'); return new Break(); case '{': return block(); default: return assign(); } } //赋值语句当作一个语句 不是表达式中 = 运算符结点 Stmt assign()throws IOException{ Stmt stmt; Token t = look; match(Tag.ID); Id id = top.get(t); if(id == null) error(t.toString() + " undeclared"); if(look.tag == '=') { move(); stmt = new Set(id,bool()); }else { Access x = offset(id); match('='); stmt = new SetElem(x,bool()); } match(';'); return stmt; } Expr bool()throws IOException { Expr x = join(); while(look.tag == Tag.OR) { Token tok = look; move(); x = new Or(tok,x,join()); } return x; } Expr join()throws IOException{ Expr x = equality(); while(look.tag == Tag.AND) { Token tok = look; move(); x = new And(tok,x,equality()); } return x; } Expr equality() throws IOException { Expr x = rel(); while( look.tag == Tag.EQ || look.tag == Tag.NE ) { Token tok = look; move(); x = new Rel(tok, x, rel()); } return x; } Expr rel() throws IOException { Expr x = expr(); switch( look.tag ) { case '<': case Tag.LE: case Tag.GE: case '>': Token tok = look; move(); return new Rel(tok, x, expr()); default: return x; } } Expr expr() throws IOException { Expr x = term(); while( look.tag == '+' || look.tag == '-' ) { Token tok = look; move(); x = new Arith(tok, x, term()); } return x; } Expr term() throws IOException { Expr x = unary(); while(look.tag == '*' || look.tag == '/' ) { Token tok = look; move(); x = new Arith(tok, x, unary()); } return x; } Expr unary() throws IOException { if( look.tag == '-' ) { move(); return new Unary(Word.minus, unary()); } else if( look.tag == '!' ) { Token tok = look; move(); return new Not(tok, unary()); } else return factor(); } Expr factor() throws IOException { Expr x = null; switch( look.tag ) { case '(': move(); x = bool(); match(')'); return x; case Tag.NUM: x = new Constant(look, Type.Int); move(); return x; case Tag.REAL: x = new Constant(look, Type.Float); move(); return x; case Tag.TRUE: x = Constant.True; move(); return x; case Tag.FALSE: x = Constant.False; move(); return x; default: error("syntax error"); return x; case Tag.ID: String s = look.toString(); Id id = top.get(look); if( id == null ) error(look.toString() + " undeclared"); move(); if( look.tag != '[' ) return id; else return offset(id); } } Access offset(Id a) throws IOException { Expr i; Expr w; Expr t1, t2; Expr loc; Type type = a.type; match('['); i = bool(); match(']'); type = ((Array)type).of; w = new Constant(type.width); t1 = new Arith(new Token('*'), i, w); loc = t1; while( look.tag == '[' ) { match('['); i = bool(); match(']'); type = ((Array)type).of; w = new Constant(type.width); t1 = new Arith(new Token('*'), i, w); t2 = new Arith(new Token('+'), loc, t1); loc = t2; } return new Access(a, loc, type); } }