RACSequence additions

Example.m

- (NSString *)stringByTrimmingWhiteSpacesForEachLine {
    return [[self.rac_lineSequence map:^id(NSString * line) {
        return [line stringByTrimmingWhiteSpaces];
    }] foldLeftWithStart:@"" reduce:^NSString *(NSString *accumulator, NSString *value) {
                          return [accumulator stringByAppendingFormat:@"%@\n", value];
                      }];
}

NSString+RACSequence.m

//
//  NSString+RACSequenceAdditions.m
//  ReactiveCocoa
//
//  Created by Justin Spahr-Summers on 2012-10-29.
//  Copyright (c) 2012 GitHub. All rights reserved.
//

#import "NSString+RACSequenceAdditions.h"
#import "RACStringSequence.h"
#import "RACTokenizedStringSequence.h"

@implementation NSString (RACSequenceAdditions)

- (RACSequence *)rac_sequence {
	return [RACStringSequence sequenceWithString:self offset:0];
}

- (RACSequence *)rac_lineSequence {
    return [self rac_sequenceWithTokenization:NSStringEnumerationByLines];
}

- (RACTokenizedStringSequence *)rac_sequenceWithTokenization:(NSStringEnumerationOptions)tokenization {
    return [RACTokenizedStringSequence sequenceWithString:self tokenization:tokenization];
}

@end

NSString+RACSequence.m(actually.h)

//
//  NSString+RACSequenceAdditions.h
//  ReactiveCocoa
//
//  Created by Justin Spahr-Summers on 2012-10-29.
//  Copyright (c) 2012 GitHub. All rights reserved.
//

#import <Foundation/Foundation.h>

@class RACSequence;
@class RACTokenizedStringSequence;

@interface NSString (RACSequenceAdditions)

/// Creates and returns a sequence containing strings corresponding to each
/// composed character sequence in the receiver.
///
/// Mutating the receiver will not affect the sequence after it's been created.
@property (nonatomic, copy, readonly) RACSequence *rac_sequence;
@property (nonatomic, copy, readonly) RACSequence *rac_lineSequence;

- (RACSequence *)rac_sequenceWithTokenization:(NSStringEnumerationOptions)tokenization;

@end

RACTokenizedSequence.m

//
//  RACTokenizedStringSequence.m
//  ReactiveCocoa
//
//  Created by Petro Korienev on 6/8/16.
//  Copyright © 2016 GitHub. All rights reserved.
//

#import "RACTokenizedStringSequence.h"

@interface RACTokenizedStringSequence ()

@property (nonatomic, assign) NSStringEnumerationOptions tokenization;
@property (nonatomic, strong) NSString *headString;
@property (nonatomic, strong) NSString *tailString;

@end

@implementation RACTokenizedStringSequence

#pragma mark Lifecycle

+ (instancetype)sequenceWithString:(NSString *)string tokenization:(NSStringEnumerationOptions)tokenization {
    
    if (!string.length) return self.empty;
    __block NSString *head = nil;
    __block NSString *tail = nil;
    [string enumerateSubstringsInRange:NSMakeRange(0, string.length)
                               options:tokenization
                            usingBlock:^(NSString *substring, NSRange substringRange, NSRange enclosingRange, BOOL *stop) {
                                     if (!head) {   // first iteration
                                         head = substring;
                                     }
                                     else { //second iteration
                                         tail = [string substringWithRange:NSMakeRange(substringRange.location, string.length - substringRange.location)];
                                         *stop = YES;
                                     }
    }];
    
    RACTokenizedStringSequence *seq = [self new];
    seq.headString = head;
    seq.tailString = tail;
    seq.tokenization = tokenization;
    return seq;
}

#pragma mark RACSequence

- (id)head {
    return self.headString;
}

- (RACSequence *)tail {
    RACSequence *sequence = [self.class sequenceWithString:self.tailString tokenization:self.tokenization];
    sequence.name = self.name;
    return sequence;
}

- (NSArray *)array {
    NSMutableArray *array = [NSMutableArray arrayWithObject:self.headString];
    
    [self.tailString enumerateSubstringsInRange:NSMakeRange(0, self.tailString.length)
                                    options:self.tokenization
                                 usingBlock:^(NSString *substring, NSRange substringRange, NSRange enclosingRange, BOOL *stop) {
        [array addObject:substring];
    }];
    
    return [array copy];
}

#pragma mark NSObject

- (NSString *)description {
    return [NSString stringWithFormat:@"<%@: %p>{ name = %@, string = %@ }", self.class, self, self.name, [self.headString stringByAppendingString:self.tailString]];
}


@end