Reorganized File Structure

Added Documentation

MathKit/MPEvaluationContext.m

@@ -0,0 +1,88 @@
+//
+//  MPEvaluationContext.m
+//  MathPad
+//
+//  Created by Kim Wittenburg on 12.09.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import "MPEvaluationContext.h"
+
+@interface MPEvaluationContext ()
+@property (nonatomic, strong) NSMutableArray *stack;
+@end
+
+@implementation MPEvaluationContext
+
+static MPEvaluationContext *sharedContext;
++ (MPEvaluationContext *)sharedContext
+{
+    if (!sharedContext) {
+        sharedContext = [[MPEvaluationContext alloc] init];
+    }
+    return sharedContext;
+}
+
+- (instancetype)init
+{
+    if (sharedContext) {
+        return sharedContext;
+    }
+    self = [super init];
+    if (self) {
+        _stack = [[NSMutableArray alloc] init];
+        [self push];
+        [self defineVariable:@"e"
+                       value:[[NSDecimalNumber alloc] initWithDouble:M_E]];
+        [self defineVariable:@"π"
+                       value:[[NSDecimalNumber alloc] initWithDouble:M_PI]];
+    }
+    return self;
+}
+
+- (void)push
+{
+    [self.stack addObject:[[NSMutableDictionary alloc] init]];
+}
+
+- (void)pop
+{
+    [self.stack removeLastObject];
+}
+
+- (BOOL)defineVariable:(NSString *)variable
+                 value:(NSDecimalNumber *)value
+{
+    [self undefineVariable:variable];
+    if ([self isVariableDefined:variable]) {
+        return NO;
+    }
+    NSMutableDictionary *currentBindings = self.stack.lastObject;
+    currentBindings[variable] = value;
+    return YES;
+}
+
+- (void)undefineVariable:(NSString *)variable
+{
+    NSMutableDictionary *currentBindings = self.stack.lastObject;
+    [currentBindings removeObjectForKey:variable];
+}
+
+- (BOOL)isVariableDefined:(NSString *)variable
+{
+    return [self valueForVariable:variable] != nil;
+}
+
+- (NSDecimalNumber *)valueForVariable:(NSString *)variable
+{
+    NSUInteger currentIndex = self.stack.count;
+    NSDictionary *currentBindings;
+    NSDecimalNumber *value = nil;
+    while (!value && currentIndex > 0) {
+        currentBindings = self.stack[--currentIndex];
+        value = currentBindings[variable];
+    }
+    return value;
+}
+
+@end