47 lines
1.2 KiB
Java
47 lines
1.2 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>CAR</code> represents the CAR function in Lisp.
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*/
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public class CAR extends LispFunction {
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// The number of arguments that CAR takes.
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private static final int NUM_ARGS = 1;
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public SExpression call(Cons argList) {
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// retrieve the number of arguments passed to CAR
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int argListLength = LENGTH.getLength(argList);
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// make sure we have received the proper number of arguments
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if (argListLength != NUM_ARGS) {
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Cons originalSExpr = new Cons(new Symbol("CAR"), argList);
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String errMsg = "too " +
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((argListLength > NUM_ARGS) ? "many" : "few") +
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" arguments given to CAR: " + originalSExpr;
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throw new RuntimeException(errMsg);
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}
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SExpression argCar = argList.getCar();
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// make sure that the argument is a list
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if (argCar.listp()) {
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Cons arg = (Cons) argCar;
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return arg.getCar();
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}
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// the argument is not a list
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throw new RuntimeException("CAR: " + argCar + " is not a list");
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}
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}
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