public Expression substitute(String var, Expression replacement) {
Vector<Expression> new_operands = new Vector<Expression>();
for (Expression o : operands) {
new_operands.add(o.substitute(var, replacement));
}
return new Application(operator.substitute(var, replacement), new_operands);
}
@Override
public void substitute(Expression oldExp, Expression newExp) {
if (exp.equals(oldExp)) {
exp = newExp;
} else {
exp.substitute(oldExp, newExp);
}
}
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;
}
/**
* Performs the substitution for <b>(LAMBDA)</b> expressions.
*
* @param id the identifier for the substitution.
* @param e the expression to substitute.
* @return the new expression.
*/
@Override
public Expression substitute(String id, Expression e) {
if (this.id.equals(id)) {
return this;
} else {
// determine the free identifiers for e
Set<String> free = e.free();
// generate a new unique identifier
String newId = this.id;
while (free.contains(newId)) newId = newId + "'";
// perform the bound renaming
Expression newE = this.e.substitute(this.id, new Identifier(newId));
// perform the substitution
return new Lambda(newId, this.tau, newE.substitute(id, e));
}
}
@Override
public void substitute(Expression oldExp, Expression newExp) {
if (target != null && target.equals(oldExp)) {
target = newExp;
}
if (target != null) {
target.substitute(oldExp, newExp);
}
for (int i = 0; i < arguments.size(); i++) {
Expression e = arguments.get(i);
if (e.equals(oldExp)) {
arguments.set(i, newExp);
}
arguments.get(i).substitute(oldExp, newExp);
}
}