// Checks if one of the operands is reducible
public boolean isOperandsReducible() {
for (Expression o : operands) {
if (o.reducible()) {
return true;
} else if (!IsValue.isValue(o)) {
return false;
}
}
return false;
}
public Expression oneStep() {
if (operator.reducible()) {
return new Application(operator.oneStep(), operands);
} else if (isOperandsReducible()) {
return new Application(operator, reduceOperandsByOneStep());
} else if (allOperandsAreValues()) {
if (operator instanceof RecFun) {
RecFun operator = ((RecFun) this.operator);
Expression body = operator.body;
// Substitute occurrences of function name with the function
body = body.substitute(operator.funVar, operator);
// When we are here, we are sure that the form is
// (fun ... end Op1 ... OpN)
Vector<String> formals = operator.formals;
for (int i = 0; i < formals.size(); i++) {
body = body.substitute(formals.get(i), operands.get(i));
}
return body;
} else if (operator instanceof Fun) {
Fun operator = ((Fun) this.operator);
Expression body = operator.body;
// When we are here, we are sure that the form is
// (fun ... end Op1 ... OpN)
Vector<String> formals = operator.formals;
for (int i = 0; i < formals.size(); i++) {
body = body.substitute(formals.get(i), operands.get(i));
}
return body;
} else {
return this;
}
}
return this;
}
// Q: When is Function Application reducible?
// A: When either its operands or operator is reducible
public boolean reducible() {
return operator.reducible()
|| (IsValue.isValue(operator) && isOperandsReducible())
|| (IsValue.isValue(operator) && allOperandsAreValues());
}