"Pipe" operator for chaining operations

[klaus triendl]

I am not sure if you have considered this possibility: I find it much more generic to provide "free functions" to decouple the extension of functionality from the core of a class than the intrusive way via member methods.
This way, the standard std::epected doesn't have to be replaced or updated by a proposal, and its use can be made even more useful.

The "pipe" operator|() can be used as a convenient way to concatenate things, and the syntax looks and feels as natural as the "dot" operator:

tl::expected<image,fail_reason> get_cute_cat (const image& img) {
    return crop_to_cat(img)
           | and_then(add_bow_tie)
           | and_then(make_eyes_sparkle)
           | map(make_smaller)
           | map(add_rainbow);
}

This would also apply to your proposal for monadic operations for std::optional.

[klaus triendl]

Oh, I see now that free functions were taken into consideration.