84 lines
2.5 KiB
Java
84 lines
2.5 KiB
Java
package function.builtin.special;
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import static function.builtin.EVAL.eval;
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import static function.builtin.predicate.EQUAL.isEqual;
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import static sexpression.Nil.NIL;
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import static sexpression.Symbol.T;
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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.Nil;
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import sexpression.SExpression;
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@FunctionNames({ "CASE" })
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public class CASE extends LispSpecialFunction {
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private ArgumentValidator argumentValidator;
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public CASE(String name) {
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this.argumentValidator = new ArgumentValidator(name);
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this.argumentValidator.setMinimumNumberOfArguments(1);
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this.argumentValidator.setTrailingArgumentExpectedType(Cons.class);
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this.argumentValidator.setTrailingArgumentExcludedType(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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SExpression key = eval(argumentList.getFirst());
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return callTailRecursive(key, (Cons) argumentList.getRest());
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}
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private SExpression callTailRecursive(SExpression key, Cons argumentList) {
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if (argumentList.isNull())
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return NIL;
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Cons clause = (Cons) argumentList.getFirst();
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Cons remainingClauses = (Cons) argumentList.getRest();
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SExpression keyList = clause.getFirst();
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if (isMatch(key, keyList))
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return evaluateConsequents(clause.getRest());
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return callTailRecursive(key, remainingClauses);
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}
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private boolean isMatch(SExpression key, SExpression keyList) {
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if (keyList.isNull())
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return false;
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else if (keyList.isCons())
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return containsMatch(key, keyList);
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return isEqual(key, keyList) || isEqual(T, keyList);
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}
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private boolean containsMatch(SExpression key, SExpression keyList) {
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for (; keyList.isCons(); keyList = advanceCons(keyList))
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if (isEqual(key, getFirst(keyList)))
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return true;
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return false;
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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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private SExpression evaluateConsequents(SExpression consequentList) {
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SExpression lastConsequentValue = NIL;
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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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}
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