(module struct mzscheme
  
  ;; don't provide reduction-relation directly, so that we can use that for the macro's name.
  (provide reduction-relation-lang
           reduction-relation-make-procs
           reduction-relation-rule-names
           reduction-relation-lws
           reduction-relation-procs
           build-reduction-relation
           reduction-relation?
           empty-reduction-relation
           (struct rule-pict (arrow lhs rhs label side-conditions fresh-vars pattern-binds)))
  
  (define-struct rule-pict (arrow lhs rhs label side-conditions fresh-vars pattern-binds))

  ;; type proc = (exp exp (any -> any) (listof any) -> (listof any)))
  ;;   a proc is a `cached' version of a make-proc, specialized to a particular langugage
  ;;   since that first application does all the work of compiling a pattern (wrt to a language),
  ;;   we want to avoid doing it multiple times, so it is cached in a reduction-relation struct

  
  ;; lang : compiled-language
  ;; make-procs = (listof (compiled-lang -> proc))
  ;; rule-names : (listof sym)
  ;; procs : (listof proc)
  (define-struct reduction-relation (lang make-procs rule-names lws procs))
  
  (define empty-reduction-relation (make-reduction-relation 'empty-reduction-relations-language
                                                            '()
                                                            '()
                                                            '()
                                                            '()))
  
  (define (build-reduction-relation orig-reduction-relation lang make-procs rule-names lws)
    (cond
      [orig-reduction-relation
       (let ([all-make-procs
              (append (reduction-relation-make-procs orig-reduction-relation)
                      make-procs)])
         (make-reduction-relation lang 
                                  all-make-procs
                                  (append (reduction-relation-rule-names orig-reduction-relation)
                                          rule-names)
                                  lws ;; only keep new lws for typesetting
                                  (map (λ (make-proc) (make-proc lang)) all-make-procs)))]
      [else
       (make-reduction-relation lang make-procs rule-names lws (map (λ (make-proc) (make-proc lang)) make-procs))])))