constrainedfn-examples.clj

(defconstrainedfn sqr
  "Calculates the square of a number."
  ([n]
     :requires
     (number? n)
     (not (zero? n))

     :ensures
     (pos? %)

     :body
     (* n n)))

(sqr 6)
;=> 36

(sqr -6)
;=> 36

(sqr 0)
;=> java.lang.AssertionError: Assert failed: (not (zero? n))

(defconstrainedfn positive-floats
  "Converts a number to a float.  Two numbers to a vector of floats."
  ([x]
     :requires
     (number? x)
     (pos? x)
     
     :ensures
     (float? %)
     
     :body
     (float x))
  ([x y]
     :requires
     (every? number? [x y])
     (every? pos?    [x y])
     
     :ensures
     (every? float? %)
     
     :body
     (str "this is a noop, meant to ensure that multi-expr bodies work")
     [(float x) (float y)]))

(positive-floats 1)
;=> 1.0

(positive-floats 1 2)
;=> [1.0 2.0]

(positive-floats -1)
; java.lang.AssertionError: Assert failed: (pos? x)

(positive-floats 1 -2)
; java.lang.AssertionError: Assert failed: (every? pos? [x y])

@goodmike I think a doc string might work, especially when I get around to throwing custom errors. I'm still chewing on this at the moment.

@samaaron This is a bit of a departure from the current defn, especially with the :body element. I'm still tweaking the syntax but maybe an eye toward eventual Clojure.core consumption would be a nice idea. ;-)