The original Railway:

https://fsharpforfunandprofit.com/rop/

And his 'Against Railway-Oriented Programming':

https://fsharpforfunandprofit.com/posts/against-railway-orie...

Ok

  if a is None:
    raise Exception()
  if a.b is None:
    raise Exception()
  if a.b.c is None:
    raise Exception()

One of the advantages of Python/Typescript style type hinting is that it avoids the mega-nested `if`s that you often have to resort to in Rust. In Rust the above would not work:

  if a.is_none() {
    bail!();
  }
  if a.b. // nope! a is still Option<>.

It may be possible to fix that when enum variants are distinct types but as it stands you often have to do lots of indenting.

How is this different from match case ok case err or from if result.val?

Well, the most basic pro is to avoid indentation and have pure function which are clear and have less assumption to take into account; if I know that my pipes always return me a result such as the one I want, and the "bad path" is discarded automatically, code is way cleaner.

Imagine a code without `if result is not None` basically!