[racket] fuzzy set representation in Racket

Hello All,

My name is Rian and I am a new Racket user and a novice programmer (Racket
is my first language). First let me say that I am very grateful for the
resources available online and the books, HTDP and Realm of Racket. I find
your teaching methods very clear and as a result I am picking up Racket
faster than I originally thought.

I am a System Science graduate student whose primary research focus is on
Fuzzy Set Theory. A fuzzy set is a collection of distinct elements where
each element has a degree of membership associated with it.

The representation I am currently using for a fuzzy set is the following:
First I create a struct called fuzzy-element which consists of 2 fields;
the first is the name of the element and the second is the elements degree
of membership to the set which ranges from 0 to 1.

;; Data Definition

#lang racket

(struct fuzzy-element (member degree-of-membership)
  #:transparent
  #:guard (lambda (member degree-of-membership type-name)
            (cond
              [(not (and (number? degree-of-membership)
                         (<= 0 degree-of-membership 1)
degree-of-membership))
               (error type-name
                      "~e is not a number between 0 and 1"
                      degree-of-membership)]
              [else (values member degree-of-membership)])))

;; fuzzy-element is (fuzzy-element Symbol Number[0, 1])
;; interp. a fuzzy-element as a struct in which:
;;         -the first field is the member's name
;;         -the second field is the respective members degree of membership

Then I combine them with a list so what I have now is a list of fuzzy
elements.

;; ListOfFuzzyElement is one of:
;; - empty
;; - (cons fuzzy-element ListOfFuzzyElement)

The problem with this data definition is that it allows for duplicate
structs with the same field-1 elements.

What I am looking to create is

;; A Fuzzy-Set is one of:
;; - empty list
;; - (cons *distinct* fuzzy-element ListOfFuzzyElement)



Ideally the type of representation I would like to use should look like:

(fuzzy-set (fuzzy-element 'a .1)
               (fuzzy-element 'b .2)
               (fuzzy-element 'c .3)
               (fuzzy-element 'a .3))

-> (fuzzy-set (fuzzy-element 'a .1)
                   (fuzzy-element 'b .2)
                   (fuzzy-element 'c .3))

Upon evaluation, the last element, (fuzzy-element 'a .3) is deleted because
there already exists a member named 'a (fuzzy-element 'a .1). It should
work exactly like the built in "set" data type, except in this case it is a
set of structures that checks the first fields of all structures and
eliminates latter duplicates.

Any guidance on how to create fuzzy-set representation this way or if you
can suggest more concise and elegant methods I would be greatly
appreciative.

Thanks,
-- 
Rian Shams
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