Think "normal" call syntax like

  foo(bar(baz(42)))

and then remove the superfluous parens

  foo bar baz 42

The expression is evaluated from right to left.

Now, let's make two of the functions into object members:

  A.foo(bar(B.baz(42)))

Remove the parens, extracting the methods from their objects, instead feeding each object as a left argument to its former member function:

  A foo bar B baz 42

This is normal APL-style call syntax; right-to-left if you want.