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.

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.