(module mutated-vars mzscheme
    
  (require-for-template mzscheme)
  (require (lib "boundmap.ss" "syntax")
           (lib "kerncase.ss" "syntax")
           (lib "trace.ss"))
  
  ;; mapping telling whether an identifer is mutated
  ;; maps id -> boolean
  (define table (make-module-identifier-mapping))
  
  ;; find and add to mapping all the set!'ed variables in form
  ;; syntax -> void
  (define (find-mutated-vars form)
    ;; syntax -> void
    (define (fmv/list lstx)
      (for-each find-mutated-vars (syntax->list lstx)))
    ;(printf "called with ~a~n" (syntax-object->datum form))
    (kernel-syntax-case* form #f (define-type-alias-internal define-typed-struct-internal require/typed-internal)     
      ;; what we care about: set!
      [(set! v e)
       (begin
         ;(printf "mutated var found: ~a~n" (syntax-e #'v))
         (module-identifier-mapping-put! table #'v #t))]
      [(define-values (var ...) expr)
       (find-mutated-vars #'expr)]
      [(#%app . rest) (fmv/list #'rest)]
      [(begin . rest) (fmv/list #'rest)]
      [(begin0 . rest) (fmv/list #'rest)]
      [(lambda _ . rest) (fmv/list #'rest)]
      [(case-lambda (_ . rest) ...) (for-each fmv/list (syntax->list #'(rest ...)))]
      [(if e1 e2) (begin (find-mutated-vars #'e1) (find-mutated-vars #'e2))]
      [(if e1 e2 e3) (begin (find-mutated-vars #'e1) (find-mutated-vars #'e1) (find-mutated-vars #'e3))]
      [(with-continuation-mark e1 e2 e3) (begin (find-mutated-vars #'e1) 
                                                (find-mutated-vars #'e1)
                                                (find-mutated-vars #'e3))]
      [(let-values ([_ e] ...) . b) (begin (fmv/list #'(e ...))
                                           (fmv/list #'b))]
      [(letrec-values ([_ e] ...) . b) (begin (fmv/list #'(e ...))
                                              (fmv/list #'b))]  
      ;; all the other forms don't have any expression subforms (like #%top)
      [_ (void)]))
  
  ;(trace find-mutated-vars)
  
  ;; checks to see if a particular variable is ever set!'d
  ;; is-var-mutated? : identifier -> boolean
  (define (is-var-mutated? id) (module-identifier-mapping-get table id (lambda _ #f)))
  
  (provide find-mutated-vars is-var-mutated?)
  
  )