56 lines
1.5 KiB
Java
56 lines
1.5 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>LESSP</code> represents the '<' function in Lisp.
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*/
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public class LESSP extends LispFunction {
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public SExpression call(Cons argList) {
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// make sure we have received at least one argument
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if (argList.nullp()) {
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Cons originalSExpr = new Cons(new Symbol("<"), argList);
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throw new RuntimeException("too few arguments given to <: " +
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originalSExpr);
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}
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SExpression firstArg = argList.getCar();
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Cons argRest = (Cons) argList.getCdr();
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// make sure that the first argument is a number
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if (firstArg.numberp()) {
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LispNumber num1 = (LispNumber) firstArg;
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if (argRest.nullp()) {
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return Symbol.T;
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}
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SExpression secondArg = argRest.getCar();
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// make sure that the second argument is a number as well
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if (secondArg.numberp()) {
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LispNumber num2 = (LispNumber) secondArg;
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if (num1.getValue() < num2.getValue()) {
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return call(argRest);
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}
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return Nil.getUniqueInstance();
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}
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throw new RuntimeException("<: " + secondArg + " is not a number");
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}
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throw new RuntimeException("<: " + firstArg + " is not a number");
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}
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}
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