60 lines
1.8 KiB
Java
60 lines
1.8 KiB
Java
package function.builtin.cons;
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import static function.builtin.cons.LIST.makeList;
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import static recursion.tail.TailCalls.done;
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import static recursion.tail.TailCalls.tailCall;
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import java.math.BigInteger;
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import function.ArgumentValidator;
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import function.FunctionNames;
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import function.LispFunction;
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import recursion.tail.TailCall;
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import sexpression.Cons;
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import sexpression.LispNumber;
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@FunctionNames({ "LENGTH" })
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public class LENGTH extends LispFunction {
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public static BigInteger getLength(Cons list) {
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LENGTH lengthFunction = new LENGTH("LENGTH");
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LispNumber length = lengthFunction.callWithoutArgumentValidation(makeList(list));
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return length.getValue();
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}
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private ArgumentValidator argumentValidator;
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public LENGTH(String name) {
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this.argumentValidator = new ArgumentValidator(name);
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this.argumentValidator.setExactNumberOfArguments(1);
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this.argumentValidator.setEveryArgumentExpectedType(Cons.class);
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}
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@Override
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public LispNumber call(Cons argumentList) {
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argumentValidator.validate(argumentList);
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return callTailRecursive(BigInteger.ZERO, argumentList).invoke();
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}
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private LispNumber callWithoutArgumentValidation(Cons argumentList) {
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return callTailRecursive(BigInteger.ZERO, argumentList).invoke();
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}
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private TailCall<LispNumber> callTailRecursive(BigInteger accumulatedLength, Cons argumentList) {
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Cons list = (Cons) argumentList.getFirst();
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Cons restOfList = makeList(list.getRest());
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if (list.isNull())
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return done(new LispNumber(accumulatedLength));
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return tailCall(() -> callTailRecursive(increment(accumulatedLength), restOfList));
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}
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private BigInteger increment(BigInteger number) {
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return number.add(BigInteger.ONE);
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}
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}
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