Clojure

bigint? predicate and generator

Details

  • Type: Feature Feature
  • Status: Open Open
  • Priority: Minor Minor
  • Resolution: Unresolved
  • Affects Version/s: Release 1.9
  • Fix Version/s: Release 1.11
  • Component/s: None
  • Labels:
  • Approval:
    Vetted

Description

Add bigint? and spec.gen support.

This part is easy:

(defn bigint?
  "Returns true if n is a BigInt"
  {:added "1.9"}
  [n] (instance? clojure.lang.BigInt n))

The generator is the tricky bit. test.check doesn't have a generator for bigints, just large-integer for things in long range. I think we'd want numbers beyond long range in a bigint generator (as that's a likely place where bugs might lie). Making a really high-quality bigint generator (with good growth and shrinking characteristics) is something that needs more thought.

http://clojure.github.io/test.check/clojure.test.check.generators.html#var-large-integer

Activity

Hide
Gary Fredericks added a comment -

In case I don't get around to making a patch, I think a generator along these lines would be a decent start:

(def gen-bigint 
  (gen/sized 
   (fn [size] 
     (let [large-integer (gen/resize size gen/large-integer)] 
       ;; scaling gives us relatively small vectors, but using  
       ;; the resized large-integer above means the numbers in 
       ;; the small vectors will still be big 
       (gen/scale #(+ 2 (/ % 20))
                  (gen/fmap (fn [xs] (+ (bigint (first xs)) (reduce * (map bigint (rest xs))))) 
                            (gen/not-empty (gen/vector large-integer))))))))
Show
Gary Fredericks added a comment - In case I don't get around to making a patch, I think a generator along these lines would be a decent start:
(def gen-bigint 
  (gen/sized 
   (fn [size] 
     (let [large-integer (gen/resize size gen/large-integer)] 
       ;; scaling gives us relatively small vectors, but using  
       ;; the resized large-integer above means the numbers in 
       ;; the small vectors will still be big 
       (gen/scale #(+ 2 (/ % 20))
                  (gen/fmap (fn [xs] (+ (bigint (first xs)) (reduce * (map bigint (rest xs))))) 
                            (gen/not-empty (gen/vector large-integer))))))))
Hide
Gary Fredericks added a comment -

If anything seems inadequate about the sizing in the above generator, I should point out that sizing in test.check is rather subtle but the requirements are also not well-defined. I'd be happy to discuss in detail.

Show
Gary Fredericks added a comment - If anything seems inadequate about the sizing in the above generator, I should point out that sizing in test.check is rather subtle but the requirements are also not well-defined. I'd be happy to discuss in detail.
Hide
Gary Fredericks added a comment -

As an update, I've put together a marvelous bigint generator that this margin is too small to contain. It might need tweaking but is probably fine for these purposes. It's not on test.check master yet but I expect it will be soon.

Show
Gary Fredericks added a comment - As an update, I've put together a marvelous bigint generator that this margin is too small to contain. It might need tweaking but is probably fine for these purposes. It's not on test.check master yet but I expect it will be soon.

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Dates

  • Created:
    Updated: