A module for organizing validations of data structures. Allows standardized ways of checking for conditions, and keeps track of the location of errors by keeping a path to each error found. Thus, if you were validating the following datastructure:
      { foo = 3;
        bar = { snoo = 34.5;
                blue = Snoot -6; }
      }

One might end up with an error with the error path:

bar.blue.Snoot : value -6 <= bound 0

By convention, the validations for a type defined in module M appear in module M, and have their name prefixed by validate_. E.g. Int.validate_positive.

Here's an example of how you would use validate with a record.

     type t =
       { foo: int;
         bar: float;
       }
     with fields

     let validate t =
       let module V = Validate in
       let w check = V.field_folder t check in
       V.of_list
         (Fields.fold ~init:[]
            ~foo:(w Int.validate_positive)
            ~bar:(w Float.validate_non_negative)
         )

And here's an example of how you would use it with a variant type:

      type t =
        | Foo of int
        | Bar of (float * int)
        | Snoo of Floogle.t

      let validate = function
        | Foo i -> V.name "Foo" (Int.validate_positive i)
        | Bar p -> V.name "Bar" (V.pair
                                   ~fst:Float.validate_positive
                                   ~snd:Int.validate_non_negative)
        | Snoo floogle -> V.name "Snoo" Floogle.validate
type t
The result of a validation. This effectively contains the list of errors, qualified by their location path
type 'a check = 'a -> t
to make function signatures easier to read
val pass : t
A result containing no errors
val fail : string -> t
A result containing a single error
val fails : string -> 'a -> ('a -> Sexplib.Sexp.t) -> t
val failf : ('a, unit, string, t) format4 -> 'a
Like sprintf or failwithf but produces a t instead of a string or exception
val of_list : t list -> t
combine multiple results, merging errors
val name : string -> t -> t
extend location path by one name
val name_list : string -> t list -> t
val fail_fn : string -> 'a check
fail_fn err returns a function that always returns fail, with err as the error message. (Note that there is no pass_fn so as to discourage people from ignoring the type of the value being passed unconditionally irrespective of type.)
val pass_bool : bool check
Check for unconditionally passing a bool
val pass_unit : unit check
Check for unconditionally passing a unit
val protect : 'a check -> 'a check
protect f x applies the validation f to x, catching any exceptions and returning them as errors.
val result : t -> unit Or_error.t
val errors : t -> string list
Returns a list of formatted error strings, which include both the error message and the path to the error.
val maybe_raise : t -> unit
If the result contains any errors, then raises an exception with a formatted error message containing a message for every error.
val valid_or_error : 'a -> 'a check -> 'a Or_error.t
val field : 'record -> ('record, 'a) Fieldslib.Field.t -> 'a check -> t
Used for validating an individual field.
val field_folder : 'record -> 'a check -> t list -> ('record, 'a) Fieldslib.Field.t -> t list
Creates a function for use in a Fields.fold.
val all : 'a check list -> 'a check
Combine a list of validation functions into one that does all validations.
val of_result : ('a -> (unit, string) Result.t) -> 'a check
Create a validation function from a function that produces a Result.t
val of_error : ('a -> unit Or_error.t) -> 'a check
val booltest : ('a -> bool) -> if_false:string -> 'a check
Create a validation function from a function that produces a bool
val pair : fst:'a check -> snd:'b check -> ('a * 'b) check
Validation functions for particular data types.
val list_indexed : 'a check -> 'a list check
Validates a list, naming each element by its position in the list (where the first position is 1, not 0
val list : name:('a -> string) -> 'a check -> 'a list check
Validates a list, naming each element using a user-defined function for computing the name
val first_failure : t -> t -> t
val of_error_opt : string option -> t
val alist : name:('a -> string) -> 'b check -> ('a * 'b) list check
Validates an association list, naming each element using a user-defined function for computing the name.