Metadata.VALIDABLESourceDescribes how to transform and validate strings into structured objects. An example of a Validable is the Yocaml_yaml module.
val from_string : string -> t Validate.tinclude Key_value.VALIDATOR with type t := tEach simple validator checks that the element of type t given as an argument respects the expected form.
val object_ : t -> (string * t) list Validate.tobject_ term checks that term is an object and extract the object as a list of string * t.
val list : t -> t list Validate.tlist term checks that term is a list (and extract it).
val atom : t -> string Validate.tatom term checks that term is an atom, like atoms in SEXP (and extract it as string).
val string : t -> string Validate.tstring term checks that term is a string (and extract it).
val boolean : t -> bool Validate.tboolean term checks that term is a boolean (and extract it).
val integer : t -> int Validate.tlist term checks that term is an integer (and extract it).
val float : t -> float Validate.tfloat term checks that term is a float (and extract it).
val text : t -> string Validate.ttext term checks that term is not an objet nor a list (and extract the value as a string).
val null : t -> unit Validate.tChecks that a value is Null.
In addition to validating that an element of type t has the expected form, a compound validator also applies an additional validation. For example string_and string_has_length 3 to validate that the element is a string and has a size of 3 (assuming the string_has_length x function exists).
val object_and : ((string * t) list -> 'a Validate.t) -> t -> 'a Validate.tobject_and validator term checks that term is an object and valid it using validator.
val list_and : (t list -> 'a Validate.t) -> t -> 'a Validate.tlist_and validator term checks that term is a list and valid it using validator.
val list_of : (t -> 'a Validate.t) -> t -> 'a list Validate.tlist_of validator term, ie: list_of int checks if term is a list that contains only values that satisfies the given validator.
val atom_and : (string -> 'a Validate.t) -> t -> 'a Validate.tatom_and validator term checks that term is an atom and valid it using validator.
val string_and : (string -> 'a Validate.t) -> t -> 'a Validate.tstring_and validator term checks that term is a string and valid it using validator.
val boolean_and : (bool -> 'a Validate.t) -> t -> 'a Validate.tboolean_and validator term checks that term is a boolean and valid it using validator.
val integer_and : (int -> 'a Validate.t) -> t -> 'a Validate.tinterger_and validator term checks that term is an integer and valid it using validator.
val float_and : (float -> 'a Validate.t) -> t -> 'a Validate.tfloat_and validator term checks that term is a float and valid it using validator.
val text_and : (string -> 'a Validate.t) -> t -> 'a Validate.ttext_and validator term checks that term is a text and valid it using validator.
val null_and : (unit -> 'a Validate.t) -> t -> 'a Validate.tnull_and validator term checks that term is a Null and valid it using validator.
As object_ returns an associative list, you have to manipulate associative list functions over and over again to validate an object correctly, fortunately there are combinators to help with object validation.
val optional_field :
?case_sensitive:bool ->
(t -> 'a Validate.t) ->
string ->
t ->
'a option Validate.toptional_field ?case_sensitive validator key term try to reach the value at the key position in term, if the key is not associated the function will apply the validation and wrap it into an option, if the association is not present the function will returns None. (case_sensitive act on the key and is false by default)
val optional_field_or :
?case_sensitive:bool ->
default:'a ->
(t -> 'a Validate.t) ->
string ->
t ->
'a Validate.toptional_field_or ?case_sensitive ~default validator key term same of optional_field but instead of wrapping the result into an option, it will apply default if the association does not exists. (case_sensitive act on the key and is false by default)
val required_field :
?case_sensitive:bool ->
(t -> 'a Validate.t) ->
string ->
t ->
'a Validate.trequired_field is like optional_field except that the association must exist, otherwise the check fails.
Let's imagine this type of data:
type user =
{ firstname : string
; lastname : string
; age : int
; activated : bool
; email : string option
}
let make_user firstname lastname age activated email =
{ firstname; lastname; age; activated; email }
;;We could validate it in this way (using the standard Applicative validation:
let validate obj =
let open Validate.Applicative in
make_user
<$> required_field string "firstname" obj
<*> required_field string "lastname" obj
<*> required_field integer "age" obj
<*> optional_field_or ~default:false boolean "activated" obj
<*> optional_field string "email" obj
;;In our previous example, we saw how to use queries on objects. Although this approach works, each validation requires the object to be deconstructed at each stage. Fortunately, it is possible, using associative lists, to deconstruct only once.
let's take our previous type and function (user and make_user):
let validate_with_assoc =
object_and (fun assoc ->
let open Validate.Applicative in
make_user
<$> required_assoc string "firstname" assoc
<*> required_assoc string "lastname" assoc
<*> required_assoc integer "age" assoc
<*> optional_assoc_or ~default:false boolean "activated" assoc
<*> optional_assoc string "email" assoc)
;;The result is identical to the previous one except that this time the object is only deconstructed once.
val optional_assoc :
?case_sensitive:bool ->
(t -> 'a Validate.t) ->
string ->
(string * t) list ->
'a option Validate.tSame of optional_field but acting on associatives lists.
val optional_assoc_or :
?case_sensitive:bool ->
default:'a ->
(t -> 'a Validate.t) ->
string ->
(string * t) list ->
'a Validate.tSame of optional_field_or but acting on associatives lists.
val required_assoc :
?case_sensitive:bool ->
(t -> 'a Validate.t) ->
string ->
(string * t) list ->
'a Validate.tSame of required_field but acting on associatives lists.