64 lines
1.9 KiB
Java
64 lines
1.9 KiB
Java
package function.builtin;
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import java.math.BigInteger;
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import function.LispFunction;
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import sexpression.*;
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/**
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* <code>LENGTH</code> represents the LENGTH function in Lisp.
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*/
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public class LENGTH extends LispFunction {
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/**
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* Returns the length of the given list.
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*
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* @param list
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* the list to determine the length of
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* @return the length of <code>list</code>
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*/
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public static int getLength(Cons list) {
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LENGTH lengthFunction = new LENGTH();
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LispNumber length = lengthFunction.call(LIST.makeList(list));
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return length.getValue().intValue(); // TODO - return BigInteger when all built-ins use
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// ArgumentValidator
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}
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public LispNumber call(Cons argList) {
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// make sure we have received at least one argument
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if (argList.nullp()) {
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Cons originalSExpr = new Cons(new Symbol("LENGTH"), argList);
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throw new RuntimeException("too few arguments given to LENGTH: " + originalSExpr);
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}
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SExpression argCar = argList.getCar();
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SExpression argCdr = argList.getCdr();
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// make sure we have received only one argument
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if (!argCdr.nullp()) {
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Cons originalSExpr = new Cons(new Symbol("LENGTH"), argList);
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throw new RuntimeException("too many arguments given to LENGTH: " + originalSExpr);
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}
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// make sure that the argument is a list
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if (argCar.listp()) {
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Cons arg = (Cons) argCar;
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if (arg.nullp()) {
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return new LispNumber(BigInteger.ZERO);
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}
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Cons cdr = LIST.makeList(arg.getCdr());
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LispNumber cdrLength = call(cdr);
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return new LispNumber(BigInteger.ONE.add(cdrLength.getValue()));
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}
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throw new RuntimeException("LENGTH: a proper list must not end with " + argCar);
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}
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}
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