Module Base_quickcheck.Shrinker

Shrinkers produce small values from large values. When a random test case fails, a shrinker finds the simplest version of the problem.

type 'a t

Basic Shrinkers

val atomic : _ t

This shrinker treats a type as atomic, never attempting to produce smaller values.

val unit : Base.unit t
val bool : Base.bool t
val char : Base.char t
val string : Base.string t
val int : Base.int t
val int32 : Base.int32 t
val int63 : Base.Int63.t t
val int64 : Base.int64 t
val nativeint : Base.nativeint t
val float : Base.float t
val sexp : Base.Sexp.t t
val option : 'a t -> 'a Base.option t
val list : 'a t -> 'a Base.list t
val both : 'a t -> 'b t -> ('a * 'b) t
val either : 'a t -> 'b t -> ('a, 'b) Base.Either.t t
val result : 'a t -> 'b t -> ('a, 'b) Base.Result.t t
val map_t : 'key t -> 'data t -> ('key, 'data, 'cmp) Base.Map.t t
val set_t : 'elt t -> ('elt, 'cmp) Base.Set.t t
val map_tree_using_comparator : comparator:('key, 'cmp) Base.Comparator.t -> 'key t -> 'data t -> ('key, 'data, 'cmp) Base.Map.Using_comparator.Tree.t t
val set_tree_using_comparator : comparator:('elt, 'cmp) Base.Comparator.t -> 'elt t -> ('elt, 'cmp) Base.Set.Using_comparator.Tree.t t

Modifying Shrinkers

val map : 'a t -> f:('a -> 'b) -> f_inverse:('b -> 'a) -> 'b t
val filter : 'a t -> f:('a -> Base.bool) -> 'a t
val filter_map : 'a t -> f:('a -> 'b Base.option) -> f_inverse:('b -> 'a) -> 'b t

Filters and maps according to f, and provides input to t via f_inverse. Only the f direction produces options, intentionally.

Shrinkers for Recursive Types

val fixed_point : ('a t -> 'a t) -> 'a t

Ties the recursive knot to shrink recursive types.

For example, here is an shrinker for binary trees:

let tree_shrinker leaf_shrinker =
  fixed_point (fun self ->
    either leaf_shrinker (both self self)
    |> map
         ~f:(function
           | First leaf -> `Leaf leaf
           | Second (l, r) -> `Node (l, r))
         ~f_inverse:(function
           | `Leaf leaf -> First leaf
           | `Node (l, r) -> Second (l, r)))
val of_lazy : 'a t Base.Lazy.t -> 'a t

Creates a t that forces the lazy argument as necessary. Can be used to tie (mutually) recursive knots.

Low-level functions

Most users will not need to call these.

val create : ('a -> 'a Base.Sequence.t) -> 'a t
val shrink : 'a t -> 'a -> 'a Base.Sequence.t