[notpushkin]

Sorry, messed up parens here. It should have been:

    a = f(e(d(c(b))), 4), 5)

b is passed to c, then the result is passed to d, then to e along with 4 as a second parameter, and finally to f along with 5.

[mg]

    a = f(e(d(c(b))), 4), 5)

That has 4 opening parenthesis and 5 closing parenthesis.

    b is passed to c

        b ~> c

    then the result is passed to d

        b ~> c ~> d

    then to e along with 4 as a second parameter

        b ~> c ~> d,4 ~> e

    and finally to f along with 5

        b ~> c ~> d,4 ~> e,5 ~> f

[notpushkin]

    b ~> c ~> d,4 ~> e

This reads as

    b ~> c ~> (d, 4) ~> e

to me. Sure, you can get used to it, but it’s pretty unnatural. Is this syntax used in any other languages?

[mg]

The nice aspect of "this ~> that" is that the meaning is simply "put this into that". And that it results in the shortest code.

An alternative would be:

    b ~> c ~> d ~> e(%,4)

Slightly longer, but maybe easier to read. Also easier to handle, as you can remove the fourth part " ~> e(%,4)" without having to change the third part.