53 lines
1.4 KiB
Java
53 lines
1.4 KiB
Java
package function.builtin.special;
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import function.ArgumentValidator;
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import function.FunctionNames;
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import function.LispSpecialFunction;
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import sexpression.Cons;
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import sexpression.SExpression;
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import static function.builtin.Eval.eval;
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@FunctionNames({ "IF" })
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public class IF extends LispSpecialFunction {
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private ArgumentValidator argumentValidator;
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public IF(String name) {
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this.argumentValidator = new ArgumentValidator(name);
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this.argumentValidator.setMinimumNumberOfArguments(2);
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this.argumentValidator.setMaximumNumberOfArguments(3);
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}
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@Override
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public SExpression call(Cons argumentList) {
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argumentValidator.validate(argumentList);
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SExpression test = eval(argumentList.getFirst());
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SExpression thenForm = getThenForm(argumentList);
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SExpression elseForm = getElseForm(argumentList);
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return isNil(test) ? eval(elseForm) : eval(thenForm);
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}
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private boolean isNil(SExpression test) {
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return test.isNull();
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}
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private SExpression getThenForm(Cons argumentList) {
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Cons expressions = getRestOfList(argumentList);
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return expressions.getFirst();
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}
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private Cons getRestOfList(Cons argumentList) {
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return (Cons) argumentList.getRest();
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}
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private SExpression getElseForm(Cons argumentList) {
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Cons expressions = getRestOfList(argumentList);
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return getRestOfList(expressions).getFirst();
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}
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}
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