Example.m

//
//  Example.m
//  Partial
//
//  Created by Robert Böhnke on 5/23/13.
//  Copyright (c) 2013 Robert Böhnke. All rights reserved.
//

#import "Partial.h"

SpecBegin(Partial)

it(@"should WTF", ^{
    BlockVar block = lift(@selector(addObject:));

    NSMutableArray *myArray = [NSMutableArray array];

    block(myArray, @1);
    block(myArray, @2);
    block(myArray, @3);

    NSLog(@"My array is now %@", myArray); // @[ @1, @2, @3 ]

    Block1 add = partial(myArray, (Block2)block);

    add(@4);
    add(@5);
    add(@6);

    NSLog(@"My array is now %@", myArray); // @[ @1, @2, @3, @4, @5, @6 ]
});

SpecEnd

Partial.h

//
//  Partial.h
//  Partialm
//
//  Created by Robert Böhnke on 5/23/13.
//  Copyright (c) 2013 Robert Böhnke. All rights reserved.
//

#import <Foundation/Foundation.h>

#define OVERLOADABLE __attribute__((overloadable))

typedef id (^Block0)(void);
typedef id (^Block1)(id arg1);
typedef id (^Block2)(id arg1, id arg2);
typedef id (^Block3)(id arg1, id arg2, id arg3);
typedef id (^Block4)(id arg1, id arg2, id arg3, id arg4);
typedef id (^Block5)(id arg1, id arg2, id arg3, id arg4, id arg5);
typedef id (^Block6)(id arg1, id arg2, id arg3, id arg4, id arg5, id arg6);

typedef id (^BlockVar)(id va, ...);

BlockVar lift(SEL selector);

OVERLOADABLE Block0 partial(id value, Block1 block);
OVERLOADABLE Block1 partial(id value, Block2 block);
OVERLOADABLE Block2 partial(id value, Block3 block);
OVERLOADABLE Block3 partial(id value, Block4 block);
OVERLOADABLE Block4 partial(id value, Block5 block);
OVERLOADABLE Block5 partial(id value, Block6 block);

Partial.m

//
//  Partial.m
//  Partial
//
//  Created by Robert Böhnke on 5/23/13.
//  Copyright (c) 2013 Robert Böhnke. All rights reserved.
//

#include <objc/objc.h>
#include <objc/objc-class.h>
#include <objc/objc-runtime.h>

#import "Partial.h"

BlockVar lift(SEL selector)
{
    return ^id(id _self, ...) {
        Method method = class_getInstanceMethod([_self class], selector);
        const char *encoding = method_getTypeEncoding(method);
        NSMethodSignature *signature = [NSMethodSignature signatureWithObjCTypes:encoding];

        NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];

        [invocation setTarget:_self];
        [invocation setSelector:selector];

        va_list args;
        va_start(args, _self);

        for (NSUInteger i = 2; i < signature.numberOfArguments; i++) {
            void *arg = va_arg(args, void *);
            [invocation setArgument:&arg atIndex:i];
        }

        va_end(args);

        [invocation invoke];

        BOOL isVoid = strcmp(signature.methodReturnType, @encode(void)) == 0;

        if (isVoid) return nil;

        id returnValue;
        [invocation getReturnValue:&returnValue];

        return returnValue;
    };
}

OVERLOADABLE Block0 partial(id value, Block1 block)
{
    return ^{
        return block(value);
    };
}

OVERLOADABLE Block1 partial(id value, Block2 block)
{
    return ^(id arg2){
        return block(value, arg2);
    };
}

OVERLOADABLE Block2 partial(id value, Block3 block)
{
    return ^(id arg2, id arg3) {
        return block(value, arg2, arg3);
    };
}

OVERLOADABLE Block3 partial(id value, Block4 block)
{
    return ^(id arg2, id arg3, id arg4) {
        return block(value, arg2, arg3, arg4);
    };
}

OVERLOADABLE Block4 partial(id value, Block5 block)
{
    return ^(id arg2, id arg3, id arg4, id arg5) {
        return block(value, arg2, arg3, arg4, arg5);
    };
}

OVERLOADABLE Block5 partial(id value, Block6 block)
{
    return ^(id arg2, id arg3, id arg4, id arg5, id arg6) {
        return block(value, arg2, arg3, arg4, arg5, arg6);
    };
}