52 lines
842 B
Java
52 lines
842 B
Java
package sexpression;
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@DisplayName("nil")
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public class Nil extends Cons {
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public static final Nil NIL = new Nil();
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private Nil() {
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super(null, null);
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super.setFirst(this);
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super.setRest(this);
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}
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@Override
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public boolean isNull() {
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return true;
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}
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@Override
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public boolean isAtom() {
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return true;
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}
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@Override
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public boolean isCons() {
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return false;
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}
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@Override
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public boolean isSymbol() {
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return true;
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}
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/**
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* The first of NIL can not be changed.
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*/
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@Override
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public void setFirst(SExpression first) {}
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/**
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* The rest of NIL can not be changed.
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*/
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@Override
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public void setRest(SExpression rest) {}
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@Override
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public String toString() {
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return "NIL";
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}
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}
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