@(next :args)
@(define space)@/ */@(end)
@(define mulop (nod))@\
   @(local op)@\
   @(space)@\
   @(cases)@\
     @{op /[*]/}@(bind nod @(intern op *user-package*))@\
   @(or)@\
     @{op /\//}@(bind (nod) @(list 'trunc))@\
   @(end)@\
   @(space)@\
@(end)
@(define addop (nod))@\
   @(local op)@(space)@{op /[+\-]/}@(space)@\
   @(bind nod @(intern op *user-package*))@\
@(end)
@(define number (nod))@\
  @(local n)@(space)@{n /[0-9]+/}@(space)@\
  @(bind nod @(int-str n 10))@\
@(end)
@(define factor (nod))@(cases)(@(expr nod))@(or)@(number nod)@(end)@(end)
@(define term (nod))@\
  @(local op nod1 nod2)@\
  @(cases)@\
    @(factor nod1)@\
    @(cases)@(mulop op)@(term nod2)@(bind nod (op nod1 nod2))@\
    @(or)@(bind nod nod1)@\
    @(end)@\
  @(or)@\
    @(addop op)@(factor nod1)@\
    @(bind nod (op nod1))@\
  @(end)@\
@(end)
@(define expr (nod))@\
  @(local op nod1 nod2)@\
  @(term nod1)@\
  @(cases)@(addop op)@(expr nod2)@(bind nod (op nod1 nod2))@\
  @(or)@(bind nod nod1)@\
  @(end)@\
@(end)
@(cases)
@  {source (expr e)}
@  (output)
source: @source
AST:    @(format nil "~s" e)
value:  @(eval e nil)
@  (end)
@(or)
@  (maybe)@(expr e)@(end)@bad
@  (output)
erroneous suffix "@bad"
@  (end)
@(end)