# Valid
A validation library for [Gleam](https://gleam.run/).
API Docs: <https://hexdocs.pm/valid>.
This library follows the principle [Parse don't validate](https://lexi-lambda.github.io/blog/2019/11/05/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
```gleam
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.
```gleam
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.
```gleam
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>
