Step support two directions

gistfile1.m

    void (^((^step)(CGFloat, CGFloat, CGFloat)))(void (^)(CGFloat)) = ^(CGFloat begin, CGFloat end, CGFloat delta) {
        if (begin <= end) {
            return (void (^)(void (^)(CGFloat)))[[^(void (^block)(CGFloat)) {
                for (CGFloat v = begin; v < end; v += delta) {
                    block(v);
                }
            } copy] autorelease];
        } else {
            return (void (^)(void (^)(CGFloat)))[[^(void (^block)(CGFloat)) {
                for (CGFloat v = begin; v >= end; v -= delta) {
                    block(v);
                }
            } copy] autorelease];
        }
    };
    
    step(fromProgress, toProgress, 0.025)(^(CGFloat progress) {
        // something must be wrong
    });