Allow DEFUN and LAMBDA with an empty body

src/function/UserDefinedFunction.java

@@ -37,7 +37,7 @@ public class UserDefinedFunction extends LispFunction {
         SymbolTable callingScope = executionContext.getScope();
         executionContext.setScope(functionScope);
 
-        SExpression lastEvaluation = null;
+        SExpression lastEvaluation = Nil.getInstance();
 
         for (Cons expression = body; expression.consp(); expression = (Cons) expression.getCdr())
             lastEvaluation = EVAL.eval(expression.getCar());

src/function/builtin/special/DEFUN.java

@@ -17,7 +17,7 @@ public class DEFUN extends LispFunction {
 
     public DEFUN() {
         this.argumentValidator = new ArgumentValidator("DEFUN");
-        this.argumentValidator.setMinimumNumberOfArguments(3);
+        this.argumentValidator.setMinimumNumberOfArguments(2);
         this.argumentValidator.setFirstArgumentExpectedType(Symbol.class);
 
         this.lambdaListIsListValidator = new ArgumentValidator("DEFUN|lambda-list|");

src/function/builtin/special/LAMBDA.java

@@ -34,7 +34,7 @@ public class LAMBDA extends LispFunction {
     public LAMBDA() {
         this.argumentValidator = new ArgumentValidator("LAMBDA");
         this.argumentValidator.setFirstArgumentExpectedType(Cons.class);
-        this.argumentValidator.setMinimumNumberOfArguments(2);
+        this.argumentValidator.setMinimumNumberOfArguments(1);
 
         this.lambdaListValidator = new ArgumentValidator("LAMBDA|lambda-list|");
         this.lambdaListValidator.setEveryArgumentExpectedType(Symbol.class);

test/function/builtin/special/DEFUNTester.java

@@ -26,7 +26,15 @@ public class DEFUNTester {
 
     @Test
     public void testDefun() {
-        String input = "(defun f () nil)";
+        String input = "(defun f () t)";
+
+        assertSExpressionsMatch(parseString("f"), evaluateString(input));
+        assertSExpressionsMatch(parseString("t"), evaluateString("(f)"));
+    }
+
+    @Test
+    public void testDefunWithEmptyBody() {
+        String input = "(defun f ())";
 
         assertSExpressionsMatch(parseString("f"), evaluateString(input));
         assertSExpressionsMatch(parseString("()"), evaluateString("(f)"));
@@ -68,8 +76,8 @@ public class DEFUNTester {
     }
 
     @Test(expected = TooFewArgumentsException.class)
-    public void testApplyWithTooFewArguments() {
-        evaluateString("(defun x ())");
+    public void testDefunWithTooFewArguments() {
+        evaluateString("(defun x)");
     }
 
 }

test/function/builtin/special/LAMBDATester.java

@@ -17,6 +17,13 @@ public class LAMBDATester {
         assertSExpressionsMatch(parseString("(LAMBDA (X) X)"), evaluateString(input));
     }
 
+    @Test
+    public void testLambdaWithNoBody() {
+        String input = "(lambda ())";
+
+        assertSExpressionsMatch(parseString("(LAMBDA ())"), evaluateString(input));
+    }
+
     @Test
     public void lambdaExpressionIsLambdaExpression() {
         Cons lambdaExpression = new Cons(new Symbol("LAMBDA"),
@@ -74,7 +81,7 @@ public class LAMBDATester {
 
     @Test(expected = TooFewArgumentsException.class)
     public void testLambdaWithTooFewArguments() {
-        evaluateString("(lambda ())");
+        evaluateString("(lambda)");
     }
 
     @Test