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Maybe monad-alike in Objective-C using parts of ReactiveCocoa and libextobjc concrete protocols
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#import <Foundation/Foundation.h> | |
#import <libextobjc/EXTConcreteProtocol.h> | |
@protocol Maybe <NSObject> | |
- (id<Maybe>)map:(id (^)(id value))block; | |
- (id<Maybe>)flattenMap:(id<Maybe> (^)(id value))block; | |
- (id<Maybe>)orElse:(id)defaultValue; | |
- (id)getOrElse:(id)defaultValue; | |
@concrete | |
- (id<Maybe>)reduce:(id (^)())reduceBlock; | |
@end | |
@interface Maybe : NSObject | |
+ (id<Maybe>)some:(id)value; | |
+ (id<Maybe>)none; | |
+ (id<Maybe>)all:(NSArray *)values some:(id<Maybe> (^)(id value))block; | |
+ (id<Maybe>)combine:(NSArray *)maybes; | |
+ (id<Maybe>)combine:(NSArray *)maybes reduce:(id (^)())reduceBlock; | |
+ (id<Maybe>)notNil:(id)value; | |
+ (id<Maybe>)value:(id)value kindOfClass:(Class)klass; | |
+ (id<Maybe>)number:(id)value; | |
+ (id<Maybe>)string:(id)value; | |
+ (id<Maybe>)strings:(id)value; | |
+ (id<Maybe>)URL:(id)value; | |
+ (id<Maybe>)array:(id)value; | |
+ (id<Maybe>)dictionary:(id)value; | |
+ (id<Maybe>)date:(id)value formatter:(NSDateFormatter *)formatter; | |
@end |
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#import "Maybe.h" | |
#import <ReactiveCocoa/RACTuple.h> | |
#import <ReactiveCocoa/RACBlockTrampoline.h> | |
@concreteprotocol(Maybe) | |
- (id<Maybe>)flattenMap:(id<Maybe> (^)(id))block { return nil; }; | |
- (id<Maybe>)map:(id (^)(id))block { return nil; }; | |
- (id<Maybe>)orElse:(id)defaultValue { return nil; } | |
- (id)getOrElse:(id)defaultValue { return nil; } | |
- (id<Maybe>)reduce:(id (^)())reduceBlock | |
{ | |
return [self map:^id(RACTuple *tuple) { | |
return [RACBlockTrampoline invokeBlock:reduceBlock withArguments:tuple]; | |
}]; | |
} | |
@end | |
@interface None : NSObject<Maybe> | |
@end | |
@interface Some : NSObject<Maybe> | |
@property (nonatomic, strong) id value; | |
- (id)initWithValue:(id)value; | |
@end | |
@implementation Maybe | |
+ (id<Maybe>)some:(id)value | |
{ | |
return [[Some alloc] initWithValue:value]; | |
} | |
+ (id<Maybe>)none | |
{ | |
static dispatch_once_t onceToken; | |
static None *none = nil; | |
dispatch_once(&onceToken, ^{ | |
none = [[None alloc] init]; | |
}); | |
return none; | |
} | |
+ (id<Maybe>)all:(NSArray *)values some:(id<Maybe> (^)(id))block | |
{ | |
id<Maybe> result = [Maybe some:@[]]; | |
for (id value in values) { | |
result = [block(value) flattenMap:^id<Maybe>(id value) { | |
return [result map:^id(NSArray *values) { | |
return [values arrayByAddingObject:value]; | |
}]; | |
}]; | |
} | |
return result; | |
} | |
+ (id<Maybe>)combine:(NSArray *)maybes | |
{ | |
return [[self all:maybes some:^id<Maybe>(id<Maybe> value) { | |
return value; | |
}] map:^id(NSArray *values) { | |
return [RACTuple tupleWithObjectsFromArray:values]; | |
}]; | |
} | |
+ (id<Maybe>)combine:(NSArray *)maybes reduce:(id (^)())reduceBlock | |
{ | |
return [[self combine:maybes] reduce:reduceBlock]; | |
} | |
+ (id<Maybe>)notNil:(id)value | |
{ | |
if (value) { | |
return [self some:value]; | |
} else { | |
return [self none]; | |
} | |
} | |
+ (id<Maybe>)value:(id)value kindOfClass:(Class)klass | |
{ | |
if (![value isKindOfClass:klass]) { | |
return [self none]; | |
} else { | |
return [self some:value]; | |
} | |
} | |
+ (id<Maybe>)number:(id)value | |
{ | |
return [self value:value kindOfClass:[NSNumber class]]; | |
} | |
+ (id<Maybe>)string:(id)value | |
{ | |
return [self value:value kindOfClass:[NSString class]]; | |
} | |
+ (id<Maybe>)strings:(id)value | |
{ | |
return [[self array:value] flattenMap:^id<Maybe>(NSArray *array) { | |
return [self all:array some:^id<Maybe>(id value) { | |
return [Maybe string:value]; | |
}]; | |
}]; | |
} | |
+ (id<Maybe>)URL:(id)value | |
{ | |
return [[self string:value] flattenMap:^id(NSString *URLString) { | |
return [self notNil:[NSURL URLWithString:URLString]]; | |
}]; | |
} | |
+ (id<Maybe>)array:(id)value | |
{ | |
return [self value:value kindOfClass:[NSArray class]]; | |
} | |
+ (id<Maybe>)dictionary:(id)value | |
{ | |
return [self value:value kindOfClass:[NSDictionary class]]; | |
} | |
+ (id<Maybe>)date:(id)value formatter:(NSDateFormatter *)formatter | |
{ | |
return [[self string:value] flattenMap:^id(NSString *dateString) { | |
return [self notNil:[formatter dateFromString:dateString]]; | |
}]; | |
} | |
@end | |
@implementation None | |
- (id<Maybe>)map:(id (^)(id))block | |
{ | |
return self; | |
} | |
- (id<Maybe>)flattenMap:(id<Maybe> (^)(id))block | |
{ | |
return self; | |
} | |
- (id<Maybe>)orElse:(id)defaultValue | |
{ | |
return [Maybe some:defaultValue]; | |
} | |
- (id)getOrElse:(id)defaultValue | |
{ | |
return defaultValue; | |
} | |
@end | |
@implementation Some | |
- (id)initWithValue:(id)value | |
{ | |
self = [super init]; | |
if (self) { | |
self.value = value; | |
} | |
return self; | |
} | |
- (id<Maybe>)map:(id (^)(id))block | |
{ | |
return [[Some alloc] initWithValue:block(self.value)]; | |
} | |
- (id<Maybe>)flattenMap:(id<Maybe> (^)(id))block | |
{ | |
return block(self.value); | |
} | |
- (id<Maybe>)orElse:(id)defaultValue | |
{ | |
return self; | |
} | |
- (id)getOrElse:(id)defaultValue | |
{ | |
return self.value; | |
} | |
@end |
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