/*
 * Abstract Syntax Tree data structures for the Straightline language,
 * "Modern Compiler Implementation in Java", Appel (w/ Palsberg),
 * Program 1.5.
 */

abstract class Stm {}

class CompoundStm extends Stm
{
   Stm stm1, stm2;
   CompoundStm(Stm s1, Stm s2)
   	{ stm1 = s1; stm2 = s2; }
}

class AssignStm extends Stm
{
   String id; Exp exp;
   AssignStm(String i, Exp e)
   	{ id = i; exp = e; }
}

class PrintStm extends Stm 
{
   ExpList exps;
   PrintStm(ExpList e)
   	{ exps = e; }
}

abstract class Exp {}

class IdExp extends Exp 
{
   String id;
   IdExp(String i) {id = i;}
}

class NumExp extends Exp 
{
   int num;
   NumExp(int n) {num = n;}
}

class OpExp extends Exp 
{
   Exp left, right; int oper;
   final static int PLUS = 1, MINUS = 2, TIMES = 3, DIV = 4;
   OpExp(Exp l, int o, Exp r)
  	 { left = l; oper = o; right = r; }
}

class EseqExp extends Exp 
{
   Stm stm; Exp exp;
   EseqExp(Stm s, Exp e)
   	{ stm = s; exp = e; }
}

abstract class ExpList {}

class PairExpList extends ExpList 
{
   Exp head; ExpList tail;
   public PairExpList(Exp h, ExpList t)
	   { head = h; tail = t; }
}

class LastExpList extends ExpList 
{
   Exp head; 
   public LastExpList(Exp h) {head = h;}
}