70 lines
1.9 KiB
Java
70 lines
1.9 KiB
Java
|
/*
|
||
|
|
* Name: Mike Cifelli
|
||
|
|
* Course: CIS 443 - Programming Languages
|
||
|
|
* Assignment: Lisp Interpreter 1
|
||
|
|
*/
|
||
|
|
|
||
|
|
package eval;
|
||
|
|
|
||
|
|
import parser.*;
|
||
|
|
|
||
|
|
/**
|
||
|
|
* <code>LENGTH</code> represents the LENGTH function in Lisp.
|
||
|
|
*/
|
||
|
|
public class LENGTH extends LispFunction {
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Returns the length of the given list.
|
||
|
|
*
|
||
|
|
* @param list
|
||
|
|
* the list to determine the length of
|
||
|
|
* @return
|
||
|
|
* the length of <code>list</code>
|
||
|
|
*/
|
||
|
|
public static int getLength(Cons list) {
|
||
|
|
LENGTH lengthFunction = new LENGTH();
|
||
|
|
LispNumber length = lengthFunction.call(LIST.makeList(list));
|
||
|
|
|
||
|
|
return length.getValue();
|
||
|
|
}
|
||
|
|
|
||
|
|
public LispNumber call(Cons argList) {
|
||
|
|
// make sure we have received at least one argument
|
||
|
|
if (argList.nullp()) {
|
||
|
|
Cons originalSExpr = new Cons(new Symbol("LENGTH"), argList);
|
||
|
|
|
||
|
|
throw new RuntimeException("too few arguments given to LENGTH: " +
|
||
|
|
originalSExpr);
|
||
|
|
}
|
||
|
|
|
||
|
|
SExpression argCar = argList.getCar();
|
||
|
|
SExpression argCdr = argList.getCdr();
|
||
|
|
|
||
|
|
// make sure we have received only one argument
|
||
|
|
if (! argCdr.nullp()) {
|
||
|
|
Cons originalSExpr = new Cons(new Symbol("LENGTH"), argList);
|
||
|
|
|
||
|
|
throw new RuntimeException("too many arguments given to LENGTH: " +
|
||
|
|
originalSExpr);
|
||
|
|
}
|
||
|
|
|
||
|
|
// make sure that the argument is a list
|
||
|
|
if (argCar.listp()) {
|
||
|
|
Cons arg = (Cons) argCar;
|
||
|
|
|
||
|
|
if (arg.nullp()) {
|
||
|
|
return new LispNumber(0);
|
||
|
|
}
|
||
|
|
|
||
|
|
Cons cdr = LIST.makeList(arg.getCdr());
|
||
|
|
LispNumber cdrLength = call(cdr);
|
||
|
|
|
||
|
|
return new LispNumber(1 + cdrLength.getValue());
|
||
|
|
}
|
||
|
|
|
||
|
|
throw new RuntimeException("LENGTH: a proper list must not end with " +
|
||
|
|
argCar);
|
||
|
|
}
|
||
|
|
|
||
|
|
}
|