[expr & forms] -> Val
Known as "thread-first".
expr through the forms, inserting
expr as the second item (first argument) of the 1st form, that form as the first argument of the 2nd form and soforth. Returns the result of the last form.
If a form is not a list, Eg. is a bare symbol, set, keyword or other structure, then a list is created with the form as the 1st element and the threaded
expr as the 2nd element.