75 lines
2.3 KiB
Java
75 lines
2.3 KiB
Java
/*
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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>APPLY</code> represents the APPLY function in Lisp.
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*/
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public class APPLY extends LispFunction {
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/**
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* Call APPLY with the specified argument list.
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*
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* @param argList
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* the list of arguments to be sent to APPLY (MUST BE A PROPER LIST)
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* @return
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* the result of evaluating APPLY on <code>argList</code>
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*/
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public static SExpression apply(Cons argList) {
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return new APPLY().call(argList);
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}
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// The number of arguments that APPLY takes.
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private static final int NUM_ARGS = 2;
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public SExpression call(Cons argList) {
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// retrieve the number of arguments passed to APPLY
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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("APPLY"), argList);
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String errMsg = "too " +
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((argListLength > NUM_ARGS) ? "many" : "few") +
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" arguments given to APPLY: " + originalSExpr;
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throw new RuntimeException(errMsg);
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}
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SExpression car = argList.getCar(); // function name
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Cons cdr = (Cons) argList.getCdr();
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SExpression cadr = cdr.getCar(); // argument list
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// make sure the second argument is a list
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if (cadr.listp()) {
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LispFunction function = EVAL.lookupFunction(car.toString());
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if (function == null) {
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// check if the car of the list is a lambda expression
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if (car.functionp()) {
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function = ((LambdaExpression) car).getFunction();
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} else if (LAMBDA.isLambdaExpression(car)) {
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Cons lexpr = (Cons) car;
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function = LAMBDA.createFunction(lexpr);
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} else {
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throw new RuntimeException("undefined function " + car);
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}
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}
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// apply the given function to the given argument list
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return function.call((Cons) cadr);
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}
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// the second argument is not a list
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throw new RuntimeException("APPLY: " + cadr + " is not a list");
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}
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}
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