formal

Type safe HTML form decoding and validation!

gleam add formal

import formal/form

// Define a type that is to be decoded from the form data
pub type SignUp {
 SignUp(email: String, password: String)
}

// This function takes the list of key-value string pairs that a HTML form
// produces. It then decodes the form data into a SignUp value, ensuring that
// all the fields are present and valid.
//
pub fn handle_form_submission(values: List(#(String, String))) {
 let result = 
   form.decoding(function.curry2(SignUp))
   |> form.with_values(values)
   |> form.field(
     "email",
     form.string
       |> form.and(form.must_not_be_empty)
       |> form.and(form.must_be_an_email),
   )
   |> form.field(
     "password",
     form.string
       |> form.and(form.must_not_be_empty)
       |> form.and(form.must_be_string_longer_than(7))
   )
   |> form.finish

 case result {
   Ok(data) -> {
     // Do something with the SignUp value here
   }
   Error(form_state) -> {
     // Re-render the form with the error messages
   }
 }
}

Further documentation can be found at https://hexdocs.pm/formal.