anchor.diff:  
   (defvar *readtables-stack* nil)
   
  -(defconstant left-bracket #\[)
  +(defconstant left-bracket #\|)
   (defconstant right-bracket #\])
   
   (defmacro enable-match-syntax ()
  
positive.code:  amatch arg &body clauses
   Same as MATCH, except that handling of algebraic types is enabled"
    (if (not (boundp 'abacus-typespec))
      (defvar abacus-typespec nil))
    `(let  ((abacus-it nil))
       (match ,arg ,@clauses)))
  
  
negative.code:            #:algebraic-match-with
             #:algebraic-guard
             #:enable-match-syntax
             #:disable-match-syntax
             :left-bracket
             :right-bracket
             :*readtables-stack*))
  