#### ppx_enumerate

Generate a list containing all values of a finite type

Generate a list containing all values of a finite type.

`ppx_enumerate` is a ppx rewriter which generates a definition for the
list of all values of a type with (for a type which only has finitely
many values).

### Basic Usage

The basic usage is simply to add "[@@deriving enumerate]" after the type
definition. For example:

``````type t =
| Foo
| Bar of bool
| Baz of [`A | `B of unit option]
[@@deriving enumerate]
``````

will produce a value `val all : t list`, whose value is equal to

``````[ Foo; Bar true; Bar false; Baz `A; Baz (`B None); Baz (`B Some ()) ]
``````

in some order (that is, there is no guarantee about the order of the list).

### Polymorphic types

In a similar fashion as sexplib, using '[@@deriving enumerate]' on polymorphic
types produces a function for [all]. For example,

``````type 'a t =
| Foo
| Bar of 'a option
[@@deriving enumerate]
``````

will produce a value `val all : 'a list -> 'a t list`, whose value is
semantically equal to

``````fun all_of_a -> Foo :: Bar None :: List.map all_of_a ~f:(fun x -> Bar (Some x))
``````

### Types not named `t`

If the type is not named `t`, then the enumeration is called
`all_of_<type_name>` instead of `all`.

### Records and Tuples

Product types are supported as well as sum types. For example,

``````type t =
{ foo : [`A | `B]
; bar : [`C | `D]
} [@@deriving enumerate]
``````

produces a `val all : t list` whose value is equal (up to order) to:

``````[ { foo = `A; bar = `C }; { foo = `A; bar = `D };
{ foo = `B; bar = `C }; { foo = `B; bar = `D };
]
``````

Tuples and variants with multiple arguments are similarly supported.

### Overriding the `all` value

Just like with sexplib, it can sometimes be useful to provide a custom
value of `all`. For example, you might define a type of bounded
integers:

``````module Small_int : sig
type t = private int [@@deriving enumerate]
val create_exn : int -> t
end = struct
type t = int
let limit = 100
let create_exn i = if i < 0 || i >= limit then failwith "out of bounds"; i
let all = List.init limit ~f:(fun i -> i)
end
``````

You could then use `Small_int.t` as normal with other types using
`[@@deriving enumerate]`:

``````type t =
| Foo
| Bar of Small_int.t option
[@@deriving enumerate]
``````

### Using `all` without defining a type name

You don't have to define a type name to be able to create the list of
values of a type. You do it for any type expression by using the `all`
quotation. For example:

``````[%all: bool * bool]
``````

which will evaluate to:

``````[ (true, true); (true, false); (false, false); (false, true) ]
``````

### Known issues

Using `all` for polymorphic variants with duplicated constructors leads
to duplicate values in the resulting lists:

``````type t = [ `A ] [@@deriving enumerate]
let () = assert ([%all: [ t | t ] ] = [ `A; `A ])
``````
Install
Published
31 May 2020
Authors
Maintainers
Sources
ppx_enumerate-v0.14.0.tar.gz
`md5=188421af960759f6e45dd748f4f08e8d`
Dependencies
ppxlib
`>= "0.11.0"`
dune
`>= "2.0.0"`
base
`>= "v0.14" & < "v0.15"`
ocaml
`>= "4.04.2"`
Reverse Dependencies
frenetic
`>= "5.0.0" & < "5.0.5"`
ppx_base
`= "v0.14.0"`