Create a loopy-env or loopy-block (WIP)

[okamsn]

Things to do:

• Add variable to say when to block commands.
• Prevent all iteration commands
• Prevent commands like skip

Things to consider:

• What should return value be?
  • Would be nice to just have the final expression be the return value.
  • Should probably still support finally-return for consistency.
• What about optimized accumulations?
  • In loopy, happens before after-do
  • What if triggered manually, such as with a (loopy-finalize)?
    • Pros: Explicit. Easy to implement after Try to use macro expansion better, such as in loopy-iter and optimized accums. #119 (commands as macros in
      loopy-iter).
    • Cons: Have to remember what to do if we don't want to use after-do,
      finally-do, or finally-return.
    • Should it be allowed only at the top level?
      • If no, how to deal with scoping issues when used inside another expand
        loopy-* macro?
        • Just expand in another step after processing the body? What if in
          multiple loopy-env? Include a loop name?
• What should commands like leave do?

;; Hypothetical example
(defmacro loopy-env (&rest args) `(ignore ,@args))
(defmacro loopy-finalize () '(progn stuff))
(loopy-env (dolist (i some-list)
             (collecting i))
           (loopy-finalize)
           loopy-result)