69 lines
2.1 KiB
Java
69 lines
2.1 KiB
Java
package function.builtin.special;
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import static function.builtin.EVAL.eval;
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import static recursion.TailCalls.done;
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import static recursion.TailCalls.tailCall;
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import static sexpression.Nil.NIL;
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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 recursion.TailCall;
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import sexpression.Cons;
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import sexpression.Nil;
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import sexpression.SExpression;
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@FunctionNames({ "COND" })
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public class COND extends LispSpecialFunction {
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private ArgumentValidator argumentValidator;
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public COND(String name) {
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this.argumentValidator = new ArgumentValidator(name);
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this.argumentValidator.setEveryArgumentExpectedType(Cons.class);
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this.argumentValidator.setEveryArgumentExcludedType(Nil.class);
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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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return callTailRecursive(argumentList).invoke();
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}
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private TailCall<SExpression> callTailRecursive(Cons argumentList) {
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if (argumentList.isNull())
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return done(NIL);
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Cons clause = (Cons) argumentList.getFirst();
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Cons remainingClauses = (Cons) argumentList.getRest();
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SExpression test = eval(clause.getFirst());
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if (isTestSuccessful(test))
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return done(evaluateConsequents(clause.getRest(), test));
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return tailCall(() -> callTailRecursive(remainingClauses));
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}
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private boolean isTestSuccessful(SExpression test) {
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return test != NIL;
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}
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private SExpression evaluateConsequents(SExpression consequentList, SExpression test) {
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SExpression lastConsequentValue = test;
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for (; consequentList.isCons(); consequentList = advanceCons(consequentList))
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lastConsequentValue = eval(getFirst(consequentList));
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return lastConsequentValue;
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}
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private SExpression advanceCons(SExpression knownCons) {
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return ((Cons) knownCons).getRest();
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}
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private SExpression getFirst(SExpression knownCons) {
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return ((Cons) knownCons).getFirst();
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}
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}
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