Module QCheck.Shrink

Shrink Values

Shrinking is used to reduce the size of a counter-example. It tries to make the counter-example smaller by decreasing it, or removing elements, until the property to test holds again; then it returns the smallest value that still made the test fail.

type 'a t = 'a -> 'a Iter.t

Given a counter-example, return an iterator on smaller versions of the counter-example.

val nil : 'a t

No shrink

val unit : unit t
  • since 0.6
val char : char t

Shrinks towards 'a'.

  • since 0.6
val char_numeral : char t

Shrinks towards '0'.

  • since 0.19
val char_printable : char t

Shrinks towards 'a' like !char. The output is also a printable character.

  • since 0.19
val int : int t
val int32 : int32 t
  • since 0.14
val int64 : int64 t
  • since 0.14
val option : 'a t -> 'a option t
val bytes : ?shrink:char t -> bytes t
  • since 0.20
val string : ?shrink:char t -> string t
val filter : ('a -> bool) -> 'a t -> 'a t

filter f shrink shrinks values the same as shrink, but only keep smaller values that satisfy f. This way it's easy to preserve invariants that are enforced by generators, when shrinking values

  • since 0.8
val int_aggressive : int t

Shrink integers by trying all smaller integers (can take a lot of time!)

  • since 0.7
val list : ?shrink:'a t -> 'a list t

Try to shrink lists by removing one or more elements.

  • parameter shrink

    if provided, will be used to also try to reduce the elements of the list themselves (e.g. in an int list one can try to decrease the integers).

val list_spine : 'a list t

Try to shrink lists by removing one or more elements.

  • since 0.10
val list_elems : 'a t -> 'a list t

Shrinks the elements of a list, without changing the list size.

  • since 0.10
val array : ?shrink:'a t -> 'a array t

Shrink an array.

  • parameter shrink

    see list

val pair : 'a t -> 'b t -> ('a * 'b) t

pair a b uses a to shrink the first element of tuples, then tries to shrink the second element using b. It is often better, when generating tuples, to put the "simplest" element first (atomic type rather than list, etc.) because it will be shrunk earlier. In particular, putting functions last might help.

val triple : 'a t -> 'b t -> 'c t -> ('a * 'b * 'c) t

Similar to pair

val quad : 'a t -> 'b t -> 'c t -> 'd t -> ('a * 'b * 'c * 'd) t

Similar to pair

val tup2 : 'a t -> 'b t -> ('a * 'b) t

tup2 a b uses a to shrink the first element of tuples, then tries to shrink the second element using b. It is often better, when generating tuples, to put the "simplest" element first (atomic type rather than list, etc.) because it will be shrunk earlier. In particular, putting functions last might help.

val tup3 : 'a t -> 'b t -> 'c t -> ('a * 'b * 'c) t

Similar to tup2

val tup4 : 'a t -> 'b t -> 'c t -> 'd t -> ('a * 'b * 'c * 'd) t

Similar to tup2

val tup5 : 'a t -> 'b t -> 'c t -> 'd t -> 'e t -> ('a * 'b * 'c * 'd * 'e) t

Similar to tup2

val tup6 : 'a t -> 'b t -> 'c t -> 'd t -> 'e t -> 'f t -> ('a * 'b * 'c * 'd * 'e * 'f) t

Similar to tup2

val tup7 : 'a t -> 'b t -> 'c t -> 'd t -> 'e t -> 'f t -> 'g t -> ('a * 'b * 'c * 'd * 'e * 'f * 'g) t

Similar to tup2

val tup8 : 'a t -> 'b t -> 'c t -> 'd t -> 'e t -> 'f t -> 'g t -> 'h t -> ('a * 'b * 'c * 'd * 'e * 'f * 'g * 'h) t

Similar to tup2

val tup9 : 'a t -> 'b t -> 'c t -> 'd t -> 'e t -> 'f t -> 'g t -> 'h t -> 'i t -> ('a * 'b * 'c * 'd * 'e * 'f * 'g * 'h * 'i) t

Similar to tup2