A little demo of partial application for variadic blocks

partial.m

#import <Foundation/Foundation.h>


#define apply(block, a) (^{ \
    switch (a.count) { \
        case 1: return block(a[0], nil); \
        case 2: return block(a[0], a[1], nil); \
        case 3: return block(a[0], a[1], a[2], nil); \
        case 4: return block(a[0], a[1], a[2], a[3], nil); \
        case 5: return block(a[0], a[1], a[2], a[3], a[4], nil); \
        case 6: return block(a[0], a[1], a[2], a[3], a[4], a[5], nil); \
        case 7: return block(a[0], a[1], a[2], a[3], a[4], a[5], a[6], nil); \
        case 8: return block(a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], nil); \
        case 9: return block(a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], nil); \
        case 10: return block(a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], a[9], nil); \
        case 11: return block(a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], a[9], a[10], nil); \
        \
        case 0: \
        default: return block(nil); \
    } \
}())


typedef id (^VariadicBlock)(id, ...);
typedef NSNumber *(^NumberOperator)(NSNumber *, ...);
typedef NSString *(^StringOperator)(NSString *, ...);


int main(int argc, char *argv[]) {
    @autoreleasepool {
        VariadicBlock (^partial)(VariadicBlock, NSArray *) = ^VariadicBlock(VariadicBlock block, NSArray *arguments) {
            return [^id(id argument, ...){
                va_list ap;
                NSMutableArray *allArguments = [arguments mutableCopy];
                
                va_start(ap, argument);
                while ([argument isKindOfClass:[NSObject class]]) {
                    [allArguments addObject:argument];
                    argument = va_arg(ap, id);
                }
                va_end(ap);
                
                return apply(block, allArguments);
            } copy];
        };
        
        NumberOperator sum = ^NSNumber *(NSNumber *number, ...) {
            if (!number) return @0;
            
            NSMutableArray *arguments = [NSMutableArray array];
            va_list ap;
            
            va_start(ap, number);
            while ([number isKindOfClass:[NSNumber class]]) {
                [arguments addObject:number];
                number = va_arg(ap, NSNumber *);
            }
            va_end(ap);
            
            NSNumber *sum = [arguments valueForKeyPath:@"@sum.integerValue"];
            
            return sum;
        };
        
        StringOperator concatenate = ^NSString *(NSString *fragment, ...) {
            if (!fragment) return @"";
                        
            NSMutableArray *arguments = [NSMutableArray array];
            va_list ap;
            
            va_start(ap, fragment);
            while ([fragment isKindOfClass:[NSString class]]) {
                [arguments addObject:fragment];
                fragment = va_arg(ap, NSString *);
            }
            va_end(ap);
            
            NSMutableString *concatenated = [NSMutableString string];
            for (NSString *fragment in arguments) {
                [concatenated appendString:fragment];
            }
            
            return concatenated;
        };
        
        NSLog(@"Sum (3): %@", sum(@1, @2));
        NSLog(@"Partially applied sum (3): %@", partial(sum, @[ @1 ])(@2, nil));
        NumberOperator sum3 = partial(sum, @[ @1, @2 ]);
        NSLog(@"Partially applied sum (6): %@", sum3(@3, nil));
        NSLog(@"Partially applied sum (10): %@", sum3(@3, @4, nil));
        NSLog(@"Concatenate (abc): %@", concatenate(@"a", @"b", @"c", nil));
        NSLog(@"Partially applied concatenate (abc): %@", partial(concatenate, @[@"a"])(@"b", @"c", nil));
    }
}