[VTimofeenko]

Asking out of lack of experience with R: how does such invocation handle case when `x` is defined with a different value at call site?

In pseudocode:

  f =
  let x = 1 in # inner vars for f go here
  arg -> arg + 1 # function logic goes here

  # example one: no external value
  f (x+1) # produces 3 (arg := (x+1) = 2; return arg +1)

  # example two: x is defined in the outer scope
  let x = 4 in
  f (x+2) # produces 5 (arg := 4; return arg + 1)? Or 3 if inner x wins as in example one?

[bnprks]

If the function chooses to overwrite the value of a variable binding, it doesn't matter how it is defined at the call site (so inner x wins in your example). In the tidyverse libraries, they often populate a lazy list variable (think python dictionary) that allows disambiguating in the case of name conflicts between the call site and programmatic bindings. But that's fully a library convention and not solved by the language.

[hugh-avherald]

Well the point is that the function can define its own logic to determine the behaviour. Users can also (with some limits) restrict the variable scope.