utils-callbacks.md
In ellmer: Chat with Large Language Models

CallbackManager catches argument mismatches

Code
  callbacks$add("foo")
Condition
  Error:
  ! `callback` must be a function, not the string "foo".
Code
  callbacks$add(function(foo) NULL)
Condition
  Error:
  ! `callback` must have the argument `data`; it currently has `foo`.
Code
  callbacks$add(function(x, y) x + y)
Condition
  Error:
  ! `callback` must have the argument `data`; it currently has `x` and `y`.

Code
  callbacks$invoke()
Condition
  Error in `private$callbacks[[as.character(id)]]()`:
  ! argument "data" is missing, with no default
Code
  callbacks$invoke(1, 2)
Condition
  Error in `private$callbacks[[as.character(id)]]()`:
  ! unused argument (2)