48 lines
1.5 KiB
Java
48 lines
1.5 KiB
Java
package function.builtin;
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import java.math.BigInteger;
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import function.*;
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import sexpression.*;
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public class MINUS extends LispFunction {
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private ArgumentValidator argumentValidator;
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public MINUS() {
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this.argumentValidator = new ArgumentValidator("-");
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this.argumentValidator.setMinimumNumberOfArguments(1);
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this.argumentValidator.setEveryArgumentExpectedType(LispNumber.class);
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}
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public SExpression call(Cons argumentList) {
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argumentValidator.validate(argumentList);
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return callTailRecursive(argumentList);
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}
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private SExpression callTailRecursive(Cons argumentList) {
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Cons remainingArguments = (Cons) argumentList.getCdr();
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SExpression firstArgument = argumentList.getCar();
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LispNumber number1 = (LispNumber) firstArgument;
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if (remainingArguments.nullp())
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return additiveInverse(number1);
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SExpression secondArgument = remainingArguments.getCar();
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LispNumber number2 = (LispNumber) secondArgument;
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LispNumber difference = new LispNumber(number1.getValue().subtract(number2.getValue()));
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SExpression remainingNumbers = remainingArguments.getCdr();
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if (!remainingNumbers.consp())
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return difference;
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return callTailRecursive(new Cons(difference, remainingNumbers));
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}
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private LispNumber additiveInverse(LispNumber number) {
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return new LispNumber(BigInteger.ZERO.subtract(number.getValue()));
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}
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}
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