== Guile and Elisp booleans and nil ==               -*- mode: org -*-

- Object is
  |      | false | null |
  | #f   | x     |      |
  | '()  |       | x    |
  | #nil | x     | x    |
  
- Procedure checks for
  |              | falsity | nullity |
  | Scheme not   | x       |         |
  | Scheme null? |         | x       |
  | Elisp not    | x       | x       |
  | Elisp null   | x       | x       |
  
- Scheme examples
  (not #f)     => #t
  (null? #f)   => #f
  (not '())    => #f
  (null? '())  => #t
  (not #nil)   => #t
  (null? #nil) => #t
  
- Elisp examples
  (not scheme-f)     => t
  (null scheme-f)    => t
  (not scheme-null)  => t
  (null scheme-null) => t
  (not nil)          => t
  (null nil)         => t

- Meaning
  There is a value that is true in Scheme, false in Elisp.
  There is a value that is non-null in Scheme, null in Elisp.
  
- Implications
  Scheme can give a true value that ends up being false in Elisp.
  Scheme can give a non-null value that ends up being null in Elisp.
  Elisp can give a false value that ends up being true in Scheme.
  Elisp can give a null value that ends up being non-null in Scheme.
  
- Really a problem?
  Find concrete examples where this causes unintuitive behavior of
  code, and/or limits expressiveness, etc.