66 lines
2.0 KiB
Java
66 lines
2.0 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 2
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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>SYMBOL_FUNCTION</code> represents the SYMBOL-FUNCTION function in
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* Lisp.
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*/
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public class SYMBOL_FUNCTION extends LispFunction {
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// The number of arguments that SYMBOL-FUNCTION 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 SYMBOL-FUNCTION
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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("SYMBOL-FUNCTION"),
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argList);
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String errMsg = "too " +
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((argListLength > NUM_ARGS) ? "many" : "few") +
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" arguments given to SYMBOL-FUNCTION: " +
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originalSExpr;
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throw new RuntimeException(errMsg);
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}
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SExpression arg = argList.getCar();
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// make sure the argument is a symbol
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if (arg.symbolp()) {
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LispFunction function = EVAL.lookupFunction(arg.toString());
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// make sure the function actually exists
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if (function != null) {
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if (function instanceof UDFunction) {
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// this is a user-defined function
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UDFunction udFunction = (UDFunction) function;
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return udFunction.getLexpr();
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}
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// this is a built-in function
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return new Symbol("SUBR-" + arg.toString());
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}
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throw new RuntimeException("SYMBOL-FUNCTION: undefined function " +
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arg);
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}
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throw new RuntimeException("SYMBOL-FUNCTION: " + arg +
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" is not a symbol");
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}
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}
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