/**
* Small-step semantics
*
* @return The expression after taking a single reduction step
*/
public Aexp reduce(Memory memory) {
if (!a1.isValue()) return new Sub(a1.reduce(memory), a2);
else if (!a2.isValue()) return new Sub(a1, a2.reduce(memory));
else return new ConstantInt(a1.value() - a2.value());
}
/**
* Compilation
*
* @return List of abstract machine (AM) instructions
*/
public Code compile() {
return a2.compile().append(a1.compile()).append(new AM.Sub());
}
/**
* Big-step semantics
*
* @return Value of the expression
*/
public int eval(Memory memory) {
return a1.eval(memory) - a2.eval(memory);
}