62 lines
1.6 KiB
Java
62 lines
1.6 KiB
Java
package function.builtin;
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import function.*;
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import sexpression.*;
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public class COND extends LispFunction {
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private ArgumentValidator argumentValidator;
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public COND() {
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this.argumentValidator = new ArgumentValidator("COND");
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this.argumentValidator.setEveryArgumentExpectedType(Cons.class);
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this.argumentValidator.doNotAcceptNil();
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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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if (argumentList.nullp())
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return Nil.getInstance();
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Cons clause = (Cons) argumentList.getCar();
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Cons remainingClauses = (Cons) argumentList.getCdr();
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SExpression test = EVAL.eval(clause.getCar());
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if (isTestSuccessful(test))
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return evaluateResult(clause, test);
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return callTailRecursive(remainingClauses);
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}
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private boolean isTestSuccessful(SExpression test) {
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return test != Nil.getInstance();
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}
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private SExpression evaluateResult(Cons clause, SExpression test) {
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SExpression lastResultValue = test;
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for (SExpression result = clause.getCdr(); result.consp(); result = advanceCons(result))
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lastResultValue = EVAL.eval(getCar(result));
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return lastResultValue;
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}
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private SExpression advanceCons(SExpression knownCons) {
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return ((Cons) knownCons).getCdr();
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}
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private SExpression getCar(SExpression knownCons) {
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return ((Cons) knownCons).getCar();
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}
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public boolean evaluateArguments() {
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return false;
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}
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}
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