@(next :args)
@(do
   (defun vig-op (plus-or-minus)
     (op + #\A [mod [plus-or-minus (- @1 #\A) (- @2 #\A)] 26]))

   (defun vig (msg key encrypt)
     (mapcar (vig-op [if encrypt + -]) msg (repeat key))))
@(coll)@{key /[A-Za-z]/}@(end)
@(coll)@{msg /[A-Za-z]/}@(end)
@(cat key "")
@(filter :upcase key)
@(cat msg "")
@(filter :upcase msg)
@(bind encoded @(vig msg key t))
@(bind decoded @(vig msg key nil))
@(bind check @(vig encoded key nil))
@(output)
text:  @msg
key:   @key
enc:   @encoded
dec:   @decoded
check: @check
@(end)