t_rp.java

中山大学编译原理课程的一个实验

/*
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package symbols;

import exceptions.ExpressionException;
import exceptions.FunctionCallException;
import exceptions.MissingOperandException;
import exceptions.SyntacticException;
import exceptions.TypeMismatchedException;
import java.util.ArrayList;

/**
 *
 * @author Beeven
 */
public class T_RP extends Terminal implements TerminalReduce{

    public Expr reduce(ArrayList<Expr> stack) throws ExpressionException {
        int post=stack.size()-1;
        Expr a= stack.get(post);  // )
        Expr o= stack.get(post-1); //bool or ae or ael //error if operand
        Expr b= stack.get(post-2); // ( or ,
        Expr c= stack.get(post-3);//$ or func or ArithExpr
        
        if(o.type==Type.lp || o.type==Type.comma)
        {
            throw new MissingOperandException();
        }
        else if(o instanceof BoolExpr) // (be) to be
        {
            stack.remove(post);
            stack.remove(post-2);
            return stack.get(post-2);
        }
        else if(o instanceof ArithExprList)
        {
            if(!(c instanceof ArithExpr)) throw new TypeMismatchedException();
            ArithExprList ael=new ArithExprList((ArithExpr)c,(ArithExprList)o);
            Expr d= stack.get(post-4);
            Expr f=stack.get(post-5);
            ArithExpr ae=null;
            if(d.type==Type.lp && f.type==Type.func) // max(ae,ael) to ae
            {
                switch(f.tag)
                {
                    case Tag.MAX:
                        ae=new ArithExpr(ael.max); break;
                    case Tag.MIN:
                        ae=new ArithExpr(ael.min); break;
                    default:
                        throw new FunctionCallException();
                }
                stack.remove(post);  //)
                stack.remove(post-1);//ael
                stack.remove(post-2);//,
                stack.remove(post-3);//ae
                stack.remove(post-4);//(
                stack.remove(post-5);//max min
                stack.add(ae);
                return ae;
            }
            else                          // ae,ael) to ael)
            {
                stack.remove(post-1);
                stack.remove(post-2);
                stack.set(post-3, ael);
                return ael;
            }
        }
        else if(o instanceof ArithExpr)
        {
            if(b.type==Type.comma) // ae,ae) to ae,ael)
            {
                ArithExprList ael = new ArithExprList((ArithExpr)o);
                stack.set(post-1, ael);
                return ael;
            }
            else if(c.type==Type.func) //sin(ae)
            {
                if(!(o instanceof ArithExpr)) throw new TypeMismatchedException();
                ArithExpr ae=null;
                switch(c.tag)
                {
                    case Tag.SIN:
                        ae=new ArithExpr(Math.sin(((ArithExpr)o).value)); break;
                    case Tag.COS:
                        ae=new ArithExpr(Math.cos(((ArithExpr)o).value)); break;
                    default:
                        throw new MissingOperandException();
                }
                stack.remove(post);
                stack.remove(post-1);
                stack.remove(post-2);
                stack.remove(post-3);
                stack.add(ae);
                return ae;
            }
            else //(ae) to ae
            {
                stack.remove(post);
                stack.remove(post-2);
                return stack.get(post-2);
            }
        }
        throw new SyntacticException();
    }

}