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