STYLE: replaced expression methods with accessors

Also added methods and documentation for the new methods:
-trueExpression, -falseExpression and -expressionBlock.
Completed documentation for -predicate and -arguments.

Foundation/CPPredicate/_CPAggregateExpression.j

@@ -25,7 +25,7 @@
 
 @implementation _CPAggregateExpression : CPExpression
 {
-    CPArray _aggregate;
+    CPArray _aggregate @accessors(getter=collection);
 }
 
 - (id)initWithAggregate:(CPArray)collection
@@ -48,11 +48,6 @@
     return YES;
 }
 
-- (id)collection
-{
-    return _aggregate;
-}
-
 - (id)expressionValueWithObject:(id)object context:(CPDictionary)context
 {
     var eval_array = [CPArray array],

Foundation/CPPredicate/_CPBlockExpression.j

@@ -23,8 +23,8 @@
 
 @implementation _CPBlockExpression :  CPExpression
 {
-    Function _block;
-    CPArray  _arguments;
+    Function _block @accessors(getter=expressionBlock);
+    CPArray  _arguments @accessors(getter=arguments);
 }
 
 - (id)initWithBlock:(Function)aBlock arguments:(CPArray)arguments
@@ -51,16 +51,6 @@
     return YES;
 }
 
-- (Function)expressionBlock
-{
-    return _block;
-}
-
-- (CPArray)arguments
-{
-    return _arguments;
-}
-
 - (id)expressionValueWithObject:(id)object context:(CPDictionary)context
 {
     var args = [];

Foundation/CPPredicate/_CPConditionalExpression.j

@@ -23,9 +23,9 @@
 
 @implementation _CPConditionalExpression :  CPExpression
 {
-    CPPredicate   _predicate;
-    CPExpression  _trueExpression;
-    CPExpression  _falseExpression;
+    CPPredicate   _predicate @accessors(getter=predicate);
+    CPExpression  _trueExpression @accessors(getter=trueExpression);
+    CPExpression  _falseExpression @accessors(getter=falseExpression);
 }
 
 - (id)initWithPredicate:(CPPredicate)aPredicate trueExpression:(CPExpression)trueExpression falseExpression:(CPExpression)falseExpression
@@ -53,21 +53,6 @@
     return YES;
 }
 
-- (CPPredicate)predicate
-{
-    return _predicate;
-}
-
-- (CPExpression)trueExpression
-{
-    return _trueExpression;
-}
-
-- (CPExpression)falseExpression
-{
-    return _falseExpression;
-}
-
 - (id)expressionValueWithObject:(id)object context:(CPDictionary)context
 {
     var eval = [_predicate evaluateWithObject:object substitutionVariables:context],

Foundation/CPPredicate/_CPConstantValueExpression.j

@@ -27,7 +27,7 @@
 
 @implementation _CPConstantValueExpression : CPExpression
 {
-    id _value;
+    id _value @accessors(getter=constantValue);
 }
 
 - (id)initWithValue:(id)value
@@ -51,11 +51,6 @@
     return YES;
 }
 
-- (id)constantValue
-{
-    return _value;
-}
-
 - (id)expressionValueWithObject:(id)object context:(CPDictionary)context
 {
     return _value;

Foundation/CPPredicate/_CPExpression.j

@@ -350,7 +350,7 @@ A dictionary that the expression can use to store temporary state for one predic
 
 /*!
     Returns the arguments for the receiver.
-    @return The arguments for the receiver—that is, the array of expressions that will be passed as parameters during invocation of the selector on the operand of a function expression.
+    @return The arguments for the receiver—that is, the array of expressions that will be passed as parameters during invocation of the selector on the operand of a function expression or as a parameter of the block of a block expression.
     This method raises an exception if it is not applicable to the receiver.
 */
 - (CPArray)arguments
@@ -371,8 +371,8 @@ A dictionary that the expression can use to store temporary state for one predic
 }
 
 /*!
-    Returns the predicate in a subquery expression.
-    @return The predicate in a subquery expression..
+    Returns the predicate in a subquery expression or a conditional expression.
+    @return The predicate in a subquery expression or a conditional expression.
     This method raises an exception if it is not applicable to the receiver.
 */
 - (CPPredicate)predicate
@@ -414,6 +414,39 @@ A dictionary that the expression can use to store temporary state for one predic
     return nil;
 }
 
+/*!
+    Returns the block of a block expression.
+    @return The block of a block expression.
+    This method raises an exception if it is not applicable to the receiver.
+*/
+- (Function)expressionBlock
+{
+    _CPRaiseInvalidAbstractInvocation(self, _cmd);
+    return nil;
+}
+
+/*!
+    Returns the true expression of a conditional expression.
+    @return The true expression of a conditional expression.
+    This method raises an exception if it is not applicable to the receiver.
+*/
+- (CPExpression)trueExpression
+{
+    _CPRaiseInvalidAbstractInvocation(self, _cmd);
+    return nil;
+}
+
+/*!
+    Returns the false expression of a conditional expression.
+    @return The false expression of a conditional expression.
+    This method raises an exception if it is not applicable to the receiver.
+*/
+- (CPExpression)falseExpression
+{
+    _CPRaiseInvalidAbstractInvocation(self, _cmd);
+    return nil;
+}
+
 - (CPExpression)_expressionWithSubstitutionVariables:(CPDictionary)variables
 {
     return self;

Foundation/CPPredicate/_CPFunctionExpression.j

@@ -28,9 +28,9 @@
 
 @implementation _CPFunctionExpression : CPExpression
 {
-    CPExpression    _operand;
+    CPExpression    _operand @accessors(getter=operand);
     SEL             _selector;
-    CPArray         _arguments;
+    CPArray         _arguments @accessors(getter=arguments);
     int             _argc;
     int             _maxargs;
 }
@@ -88,16 +88,6 @@
     return [self _function];
 }
 
-- (CPArray)arguments
-{
-    return _arguments;
-}
-
-- (CPExpression)operand
-{
-    return _operand;
-}
-
 - (id)expressionValueWithObject:(id)object context:(CPDictionary)context
 {
     var target = [_operand expressionValueWithObject:object context:context],

Foundation/CPPredicate/_CPSetExpression.j

@@ -25,8 +25,8 @@
 
 @implementation _CPSetExpression : CPExpression
 {
-    CPExpression _left;
-    CPExpression _right;
+    CPExpression _left  @accessors(getter=leftExpression);
+    CPExpression _right @accessors(getter=rightExpression);
 }
 
 - (id)initWithType:(int)type left:(CPExpression)left right:(CPExpression)right
@@ -88,16 +88,6 @@
     return self;
 }
 
-- (CPExpression)leftExpression
-{
-    return _left;
-}
-
-- (CPExpression)rightExpression
-{
-    return _right;
-}
-
 - (CPString)description
 {
     var desc;

Foundation/CPPredicate/_CPSubqueryExpression.j

@@ -26,9 +26,9 @@
 
 @implementation _CPSubqueryExpression : CPExpression
 {
-    CPExpression _collection;
+    CPExpression _collection @accessors(getter=collection);
     CPExpression _variableExpression;
-    CPPredicate  _subpredicate;
+    CPPredicate  _subpredicate @accessors(getter=predicate);
 }
 
 - (id)initWithExpression:(CPExpression)collection usingIteratorVariable:(CPString)variable predicate:(CPPredicate)subpredicate
@@ -81,21 +81,11 @@
     return YES;
 }
 
-- (CPExpression)collection
-{
-    return _collection;
-}
-
 - (id)copy
 {
     return [[_CPSubqueryExpression alloc] initWithExpression:[_collection copy] usingIteratorExpression:[_variableExpression copy] predicate:[_subpredicate copy]];
 }
 
-- (CPPredicate)predicate
-{
-    return _subpredicate;
-}
-
 - (CPString)description
 {
     return [self predicateFormat];

Foundation/CPPredicate/_CPVariableExpression.j

@@ -29,7 +29,7 @@
 
 @implementation _CPVariableExpression :  CPExpression
 {
-    CPString _variable;
+    CPString _variable @accessors(getter=variable);
 }
 
 - (id)initWithVariable:(CPString)variable
@@ -54,11 +54,6 @@
     return YES;
 }
 
-- (CPString)variable
-{
-    return _variable;
-}
-
 - (id)expressionValueWithObject:object context:(CPDictionary)context
 {
     var expression = [self _expressionWithSubstitutionVariables:context];