Valid

A validation library for Gleam.

This library follows the principle Parse don’t validate.

The current version (v4) contains two APIs. The main one using pipelines. And a experimental one using use.

New experimental API

import valid/experimental as valid

fn user_validator(input: InputUser) {
  use age <- valid.check(input.age, valid.int_min(13, "Should be at least 13"))

  use name <- valid.check(input.name, valid.string_is_not_empty("Missing name"))

  use email <- valid.check(input.email, valid.string_is_email("Missing email"))

  valid.ok(ValidUser(age:, name:, email:))
}

let input = InputUser(age: 14, name: "Sam", email: "sam@sample.com")

let result = input
 |> valid.validate(user_validator)

 result ==
 Ok(ValidUser(14, "Sam", "sam@sample.com"))

Creating a custom validator

A validator is a function that takes an input, and returns a tuple #(output, errors).

E.g.

import valid/experimental as valid

fn is_99(input) {
  case input == 99 {
    True -> #(input, [])
    False -> #(0, ["Not 99"])
  }
}

fn validator(input) {
  use out <- valid.check(input, is_99)
  valid.ok(out)
}

A validator must return a default value. This is so we can collect all the errors for all validators (instead of returning early).

Pipeline API

Original API using pipelines.

import valid

fn user_validator(user: InputUser) -> ValidatorResult(ValidUser, String) {
  valid.build3(ValidUser)
  |> valid.check(user.name, valid.is_some("Please provide a name"))
  |> valid.check(user.email, valid.is_some("Please provide an email"))
  |> valid.check(user.age, valid.ok())
}

case user_valid(input) {
  Ok(valid_user) -> ...
  Error(errors) -> ...
}

Usage and Examples (Pipeline API)

For basic usage see <test/valid/v4/basic_test.gleam>

Validators

For string validators, see <test/valid/v4/validator_string_test.gleam>
For int validators, see <test/valid/v4/validator_int_test.gleam>
For list validators, see <test/valid/v4/validator_list_test.gleam>
For optional validators, see <test/valid/v4/validator_option_test.gleam>
For creating a custom validator, see <test/valid/v4/validator_custom_test.gleam>

Composition

For composing validators, see <test/valid/v4/composition_test.gleam>

Other

For validating a dictionary, see <test/valid/v4/dictionary_test.gleam>
For custom error types, see <test/valid/v4/custom_error_test.gleam>
For validating a whole structure, see <test/valid/v4/whole_test.gleam>