Validator

A validation library for Gleam.

This library follows the principle Parse don't validate.

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).

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:

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)
}

Test

rebar3 compile
rebar3 eunit

Installation

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

{deps, [
    gleam_validator
]}.