Module QCheck2.Tree

A tree represents a generated value and its successive shrunk values.

Conceptually a pseudo-randomly generated value is packaged with its shrunk values. This coupling - called "integrated shrinking" - in a single type has a major benefit: most generators get shrinking "for free" by composing from smaller generators, and shrinking does not break invariants (e.g. shrinks of a positive number are always positive).

type 'a t

A tree of random generated values, where the root contains the value used for the test, and the sub-trees contain shrunk values (as trees, to be able to shrink several times a value) used if the test fails.

val root : 'a t -> 'a

root tree returns the root value of the tree of generated values t.

val children : 'a t -> 'a t Stdlib.Seq.t

children tree returns the direct sub-trees of the tree of generated values t.

val pp : ?depth:int -> ( Stdlib.Format.formatter -> 'a -> unit ) -> Stdlib.Format.formatter -> 'a t -> unit

pp ?depth pp_a ppf tree pretty-prints the tree of generated values tree using the pretty-print formatter ppf. Values of type 'a will be printed using the given pretty-printer pp_a.

As a tree t can be potentially huge when fully evaluated, you can control the maximum depth the printer goes with depth.

  • None means "everything"
  • 0 means "only the root"
  • 1 means "the root and its direct shrinks"
  • 2 means "the root, its direct shrinks, and the shrinks of its shrinks"
  • etc.