What is this?
ppx_deriving_crowbar is a ppx_deriving plugin for generating crowbar generators.
type number = int [@@deriving crowbar]
will result in a function which maps Crowbar's
int generator primitive to a
let number_to_crowbar : t Crowbar.gen = Crowbar.(map [int] (fun a -> a))
You can specify a custom generator to replace the automatically derived one with
[@generator f]. (This is useful in large mutually-recursive type definitions, where you want most of the automatically derived functions.) For example:
type p = int and q = p list and r = q list [@generator Crowbar.const ] [@@deriving crowbar]
to create the following functions:
let p_to_crowbar : p Crowbar.gen = Crowbar.(map [int] fun a -> a) and q_to_crowbar : q Crowbar.gen = Crowbar.list p_to_crowbar and r_to_crowbar : r Crowbar.gen = Crowbar.const 
Note that types named
t get functions named
to_crowbar, rather than
t_to_crowbar, as is the convention for
ppx_deriving_crowbar is used in tandem with
ppx_import to automatically generate OCaml ASTs to test
ocaml-migrate-parsetree in ocaml-test-omp, and to generate certificates to test
ocaml-x509 in ocaml-test-x509.