127 lines
3.9 KiB
Java
127 lines
3.9 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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import sexpression.Cons;
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import sexpression.SExpression;
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import sexpression.Symbol;
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import java.util.ArrayList;
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/**
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* A <code>UDFunction</code> is an internal representation of a user-defined
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* function in the Lisp programming language.
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*/
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public class UDFunction extends LispFunction {
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// the number of arguments that this user-defined function takes.
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private final int NUM_ARGS;
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private String name;
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private Cons body;
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private Cons lexpr;
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private SymbolTable environment;
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private ArrayList<String> parameters;
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/**
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* Create a new user-defined function with the specified name, lambda list
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* and body.
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*
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* @param name
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* the name of this user-defined function
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* @param lambdaList
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* a list of the formal parameters of this user-defined function (MUST BE
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* A PROPER LIST)
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* @param body
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* the body of this user-defined function (MUST BE A PROPER LIST)
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*/
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public UDFunction(String name, Cons lambdaList, Cons body) {
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this.name = name;
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this.body = body;
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this.lexpr = new Cons(new Symbol(name), new Cons(lambdaList, body));
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this.environment = SETF.getEnvironment();
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this.parameters = new ArrayList<String>();
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// retrieve the names of all the formal parameters of this function
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while (lambdaList.consp()) {
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this.parameters.add(lambdaList.getCar().toString());
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lambdaList = (Cons) lambdaList.getCdr();
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}
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this.NUM_ARGS = this.parameters.size();
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}
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public SExpression call(Cons argList) {
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// retrieve the number of arguments passed to this 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(name), argList);
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String errMsg = "too " +
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((argListLength > NUM_ARGS) ? "many" : "few") +
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" arguments given to " + name + ": " +
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originalSExpr;
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throw new RuntimeException(errMsg);
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}
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// push a new symbol table onto this function's environment (for its
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// parameters)
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environment = new SymbolTable(environment);
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// bind the values of the arguments to the formal parameter names
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for (String param : parameters) {
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SExpression currentArg = argList.getCar();
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environment.put(param, currentArg);
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argList = (Cons) argList.getCdr();
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}
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// store the environment of the S-expression that called this function
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// (the current environment)
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SymbolTable currentEnvironment = SETF.getEnvironment();
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// replace the current environment with the environment of this
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// function
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SETF.setEnvironment(environment);
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Cons currentSExpression = body;
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SExpression retval = null;
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// evaluate all the S-expressions making up this function's body
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while (currentSExpression.consp()) {
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retval = EVAL.eval(currentSExpression.getCar());
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currentSExpression = (Cons) currentSExpression.getCdr();
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}
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// replace the environment of the S-expression that called this
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// function
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SETF.setEnvironment(currentEnvironment);
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// remove the bindings of the arguments to the formal parameter names
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// in the environment of this function
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environment = new SymbolTable(environment.getParent());
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return retval;
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}
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/**
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* Return the lambda expression that represents this user-defined function.
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*
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* @return
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* the lambda expression that represents this user-defined function
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*/
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public Cons getLexpr() {
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return lexpr;
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}
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}
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