Terrible UI. I found two example functions (call them `f` and `g`), found the dropdown to change the input type of `f` from "string" to "function call", and even manage to get `g` suggested when I enter it's unique identifier - but cannot set up any configuration to compute `f(g(x))` (even after exhaustively trying all options).

It seems like it should be a core functionality of such a project to easily set up complex computations as function compositions.