Quickcheck.Observer
SourceAn 'a Quickcheck.Observer.t
represents a hash function on 'a
. Observers are used to construct distributions of random functions; see Quickcheck.Generator.fn
.
Like generators, observers have a ~size
argument that is threaded through to bound the depth of recursion in potentially infinite cases. For finite values, size
can be ignored.
For hashable types, one can construct an observer using of_hash
. For other types, use the built-in observers and observer combinators below, or use create
directly.
of_hash
creates an observer for any hashable type.
doubleton f
maps values to two "buckets" (as described in t
above), depending on whether they satisfy f
.
enum n ~f
maps values to n
buckets, where f
produces the index for a bucket from 0
to n-1
for each value.
of_list list ~equal
maps values in list
to separate buckets, and compares observed values to the elements of list
using equal
.
Fixed point observer for recursive types. For example:
let sexp_obs =
fixed_point (fun sexp_t ->
unmap (variant2 string (list sexp_t))
~f:(function
| Sexp.Atom atom -> `A atom
| Sexp.List list -> `B list))
of_predicate t1 t2 ~f
combines t1
and t2
, where t1
observes values that satisfy f
and t2
observes values that do not satisfy f
.
comparison ~compare ~eq ~lt ~gt
combines observers lt
and gt
, where lt
observes values less than eq
according to compare
, and gt
observes values greater than eq
according to compare
.
maps all values to a single bucket.
unmap t ~f
applies f
to values before observing them using t
.
Observer for function type. fn gen t
observes a function by generating random inputs from gen
, applying the function, and observing the output using t
.
of_fun f
produces an observer that lazily applies f
.
It is recommended that f
should not do a lot of expensive work and should not be memoized. Instead, spread out the work of generating an observer over many of_fun
calls combined with, e.g., variant
or tuple
. This allows lazily generated observers to be garbage collected after each test and the relevant portions cheaply recomputed in subsequent tests, rather than accumulating without bound over time.