Functional Programming methods for Objective C

NSArray+FP.h

//
//  NSArray+FP.h
//
//  Created by Kaio Brito on 09/01/18.
//

#import <Foundation/Foundation.h>

typedef id(^MapBlock)(id);
typedef BOOL(^FilterBlock)(id);
typedef id(^ReduceBlock)(id, id);

@interface NSArray (FP)
- (id) reduce: (ReduceBlock) block initial: (id) initialValue;
- (NSArray *) filter: (FilterBlock) block;
- (NSArray *) flatMap: (MapBlock) block;
- (NSArray *) map: (MapBlock) block;
@end

NSArray+FP.m

//
//  NSArray+FP.m
//
//  Created by Kaio Brito on 09/01/18.
//

@implementation NSArray (FP)
- (NSArray *) map: (MapBlock) block {
    NSMutableArray *resultArray = [[NSMutableArray alloc] init];
    for (id object in self) {
        [resultArray addObject:block(object)];
    }
    return resultArray;
}

- (NSArray *) filter: (FilterBlock) block {
    return [self filteredArrayUsingPredicate: [NSPredicate predicateWithBlock:^BOOL(id  _Nullable evaluatedObject, NSDictionary<NSString *,id> * _Nullable bindings) {
        return block(evaluatedObject);
    }]];
}

- (NSArray *) flatMap: (MapBlock) block {
    return [[self map:block] filter:^BOOL(id object) {
        return object != nil;
    }];
}

- (id) reduce: (ReduceBlock) block initial: (id) initialValue {
    for (id item in self) {
        initialValue = block(initialValue, item);
    }
    return initialValue;
}
@end