Function and member generators

[mmontone]

Hi.

Thanks for writing this nice library. I'm using it to generate random data from schemas: https://mmontone.github.io/schemata/#Data-generation

I'm missing some generators, and I thought I'd share my views.

One, the possibility of lifting a function (including a lambda) as generator.

https://github.com/mmontone/schemata/blob/3ed6f36cbc227ccf69bb0d62d3037ed325d7a2ed/generators.lisp#L16C1-L30

This is my current implementation:

 (defclass func (check-it::custom-generator)
    ((check-it::bias :initform 1.0
                     :accessor check-it::bias
                     :allocation :class)
     (func :initarg :func)))
  (setf (get 'func 'check-it::genex-type) 'generator)
  (setf (get 'func 'check-it::generator-form)
        `(lambda ,'(func) (make-instance ','func ,@'(:func func))))

  (defmethod generate ((generator func))
    (let ((func (slot-value generator 'func)))
      (funcall func)))
  )

and this is how you can use: (generator (func (lambda () (1+ (random 100))))).

I find this generator extremely valuable as it lets me plug arbitrary in-line functions that return random data easily.

This implementation doesn't work because it caches the result:

(def-generator func (func)
  (generator (funcall func)))

But this alternative implementation does work, and is simpler and more direct:

(defmethod check-it::generate ((generator function))
  (funcall generator))

The other generator, is a "member-of" generator, that chooses a random element from a collection (list, hash-table, or other).

This is my current implementation:

https://github.com/mmontone/schemata/blob/3ed6f36cbc227ccf69bb0d62d3037ed325d7a2ed/generators.lisp#L37-L48

I'm using that one quite a lot of too.

I'm using like:

(defparameter *person-names*
  (list "John" "Peter" "Stan" "Steve" "Wendy" "Caroline"))

(def-generator person-name-generator ()
  (generator (member-of *person-names*)))

(def-generator age-generator ()
  (generator (func (lambda () (1+ (random 100))))))

(defschema person
    (object person
            ((name string :generator (generator (person-name-generator)))
             (age integer :required nil
                          :generator (generator (age-generator))))))

So, it would be nice that some implementation of these generators be included as part of check-it, in my opinion.