Validator

A validation library for Gleam.

API Docs: https://hexdocs.pm/gleam_validator.

This library follows the principle Parse don’t validate.

Usage

You start with an input type and validate into an output type. These two types can be different. For example:

type UserInput { UserInput(name: Option(String), age: Int) }

type ValidUser { ValidUser(name: String, age: Int) }

Then you create a validator like:

import validator
import validator/common.{ValidatorResult}
import validator/int
import validator/option

fn user_validator(user: UserInput) -> ValidatorResult(ValidUser, String) {
 validator.build2(ValidUser)
 |> validator.validate(user.name, option.is_some("Please provide a name"))
 |> validator.validate(user.age, int.min(13, "Must be at least 13 years old"))
}

And run it:

case user_validator(input) {
 Ok(valid_user) -> ...
 Error(tuple(first_error, all_errors)) -> ...
}

Error type

Errors can be your own type e.g.

import validator
import validator/common.{ValidatorResult}
import validator/int
import validator/option

type Error {
 ErrorEmptyName,
 ErrorTooYoung,
}

fn user_validator(user: UserInput) -> ValidatorResult(ValidUser, String) {
 validator.build2(ValidUser)
 |> validator.validate(user.name, option.is_some(ErrorEmptyName))
 |> validator.validate(user.age, int.min(13, ErrorTooYoung))
}

ValidatorResult

ValidatorResult(valid, error) is an alias for Result(valid, tuple(error, List(error)))

The Ok branch has the valid output.

The Error branch has a tuple tuple(error, List(error)). The first value is the first error. The second value is a list with all errors (including the first).

Validators

See the API Docs for the list of included validators.

Custom property validator

A property validator has two components:

• The error to return
• A function that transforms the property if successful (fn(input) -> Option(output))

Example:

import gleam/option.{None, Option, Some}
import validator

fn bigger_than_10(num: Int) -> Option(num) {
 case num > 10 {
   True ->
     Some(num)
   False ->
     None
 }
}

let custom = validator.custom("Must be bigger than 10", bigger_than_10)

let validator = fn(form: FormInput) {
 validator.build1(ValidForm)
 |> validator.validate(form.quantity, custom)
}

Examples

See the tests for many examples

Test

rebar3 compile
rebar3 eunit

Installation

This package can be installed by adding gleam_validator to your rebar.config dependencies:

{deps, [
   gleam_validator
]}.