anchor.diff:     - A symbol
      - A key
      - A function"
  -  (/= (type# x) "table"))
  +  (or (/= (type# x) "table")
  +      (and (= (type# x) "table")
  +           (or (= (get-idx x :tag) "symbol")
  +               (= (get-idx x :tag) "key")))))
   
   (defun falsey? (x)
     "Check whether X is falsey, that is, it is either `false` or does
  
positive.code: 
  (defun boolean? (x)
    "Check whether X is a boolean."
    (= (type x) "boolean"))
  
  (defun function? (x)
    "Check whether X is a function."
  
negative.code: 
  (defun string? (x)
    "Check whether X is a string."
    (or (= (type# x) "string")
        (and (= (type# x) "table")
             (= (get-idx x :tag) "string"))))
  
  (defun number? (x)
    "Check whether X is a number."
    (or (= (type# x) "number")
        (and (= (type# x) "table")
             (= (get-idx x :tag) "number"))))
  
  (defun symbol? (x)
    "Check whether X is a symbol."
  