Started refactoring UserDefinedFunction

src/function/UserDefinedFunction.java

@@ -12,7 +12,7 @@ public class UserDefinedFunction extends LispFunction {
     private String name;
     private Cons body;
     private Cons lambdaExpression;
-    private SymbolTable environment;
+    private SymbolTable scope;
     private ArrayList<String> formalParameters;
     private ArgumentValidator argumentValidator;
 
@@ -20,7 +20,7 @@ public class UserDefinedFunction extends LispFunction {
         this.name = name;
         this.body = body;
         this.lambdaExpression = new Cons(new Symbol(name), new Cons(lambdaList, body));
-        this.environment = SETF.getSymbolTable();
+        this.scope = SETF.getSymbolTable();
 
         for (this.formalParameters = new ArrayList<>(); lambdaList.consp(); lambdaList = (Cons) lambdaList.getCdr())
             this.formalParameters.add(lambdaList.getCar().toString());
@@ -29,46 +29,52 @@ public class UserDefinedFunction extends LispFunction {
         this.argumentValidator.setExactNumberOfArguments(this.formalParameters.size());
     }
 
-    public SExpression call(Cons argList) {
-        argumentValidator.validate(argList);
-
-        // push a new symbol table onto this function's environment (for its
-        // parameters)
-        environment = new SymbolTable(environment);
+    public SExpression call(Cons argumentList) {
+        argumentValidator.validate(argumentList);
 
         // bind the values of the arguments to the formal parameter names
-        for (String param : formalParameters) {
-            SExpression currentArg = argList.getCar();
-            environment.put(param, currentArg);
-            argList = (Cons) argList.getCdr();
-        }
+        bindParameterValues(argumentList);
 
         // store the environment of the S-expression that called this function
         // (the current environment)
-        SymbolTable currentEnvironment = SETF.getSymbolTable();
+        SymbolTable callingScope = SETF.getSymbolTable();
 
         // replace the current environment with the environment of this
         // function
-        SETF.setSymbolTable(environment);
+        SETF.setSymbolTable(scope);
 
         Cons currentSExpression = body;
-        SExpression retval = null;
+        SExpression lastValue = null;
 
         // evaluate all the S-expressions making up this function's body
         while (currentSExpression.consp()) {
-            retval = EVAL.eval(currentSExpression.getCar());
+            lastValue = EVAL.eval(currentSExpression.getCar());
             currentSExpression = (Cons) currentSExpression.getCdr();
         }
 
         // replace the environment of the S-expression that called this
         // function
-        SETF.setSymbolTable(currentEnvironment);
+        SETF.setSymbolTable(callingScope);
 
         // remove the bindings of the arguments to the formal parameter names
         // in the environment of this function
-        environment = new SymbolTable(environment.getParent());
+        releaseParameterValues();
 
-        return retval;
+        return lastValue;
+    }
+
+    private void bindParameterValues(Cons argumentList) {
+        scope = new SymbolTable(scope);
+
+        for (String parameter : formalParameters) {
+            SExpression currentArg = argumentList.getCar();
+            scope.put(parameter, currentArg);
+            argumentList = (Cons) argumentList.getCdr();
+        }
+    }
+
+    private void releaseParameterValues() {
+        scope = new SymbolTable(scope.getParent());
     }
 
     public Cons getLambdaExpression() {