74 lines
2.1 KiB
Java
74 lines
2.1 KiB
Java
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/*
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* Name: Mike Cifelli
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* Course: CIS 443 - Programming Languages
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* Assignment: Lisp Interpreter 1
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*/
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package eval;
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import parser.*;
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/**
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* <code>COND</code> represents the COND form in Lisp.
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*/
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public class COND extends LispFunction {
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public SExpression call(Cons argList) {
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if (argList.nullp()) {
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// return NIL if there are were no arguments passed to COND
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return Nil.getUniqueInstance();
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}
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SExpression argCar = argList.getCar(); // first clause
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Cons argCdr = (Cons) argList.getCdr(); // list of remaining clauses
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// make sure the first clause is a list and is not NIL
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if (argCar.consp()) {
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Cons clause = (Cons) argCar;
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SExpression test = EVAL.eval(clause.getCar());
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if (test != Nil.getUniqueInstance()) {
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// the car of this clause is true, so we evaluate its cdr
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SExpression cdr = clause.getCdr();
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SExpression retval = test;
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// evaluate all the S-expressions in the cdr of the clause
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while (cdr.consp()) {
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retval = EVAL.eval(((Cons) cdr).getCar());
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cdr = ((Cons) cdr).getCdr();
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}
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// return the value of the last S-expression evaluated
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return retval;
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}
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// the car of this clause is false, so we test any remaining
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// clauses
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// check if the list of remaining clauses is a list and is not NIL
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if (argCdr.consp()) {
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return call(argCdr);
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}
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// there are no remaining clauses, so we return NIL
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return Nil.getUniqueInstance();
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}
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throw new RuntimeException("COND: clause " + argCar +
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" should be a list");
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}
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/**
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* Determine if the arguments passed to this Lisp function should be
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* evaluated.
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*
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* @return
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* <code>false</code>
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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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