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gleam_validator

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A Gleam validator

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<h1>Validator</h1>

<p>A validation library for <a href="https://gleam.run/">Gleam</a>.</p>

<p>This library follows the principle <a href="https://lexi-lambda.github.io/blog/2019/11/05/parse-don-t-validate/">Parse don't validate</a>.</p>

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

<pre><code class="language-haskell">type UserInput { UserInput(name: Option(String), age: Int) }



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

</code></pre>

<p>Then you create a validator like:</p>

<pre><code class="language-haskell">import validator

import validator/common.{ValidatorResult}

import validator/int

import validator/option



fn user_validator(user: UserInput) -&gt; ValidatorResult(ValidUser, String) {

  validator.build2(ValidUser)

  |&gt; validator.validate(user.name, option.is_some(&quot;Please provide a name&quot;))

  |&gt; validator.validate(user.age, int.min(13, &quot;Must be at least 13 years old&quot;))

}

</code></pre>

<p>And run it:</p>

<pre><code class="language-rust">case user_validator(input) {

  Ok(valid_user) -&gt; ...

  Error(tuple(first_error, all_errors)) -&gt; ...

}

</code></pre>

<h2>Error type</h2>

<p>Errors can be your own type e.g.</p>

<pre><code class="language-haskell">import validator

import validator/common.{ValidatorResult}

import validator/int

import validator/option



type Error {

  ErrorEmptyName,

  ErrorTooYoung,

}



fn user_validator(user: UserInput) -&gt; ValidatorResult(ValidUser, String) {

  validator.build2(ValidUser)

  |&gt; validator.validate(user.name, option.is_some(ErrorEmptyName))

  |&gt; validator.validate(user.age, int.min(13, ErrorTooYoung))

}

</code></pre>

<h2>ValidatorResult</h2>

<p><code>ValidatorResult(valid, error)</code> is an alias for <code>Result(valid, tuple(error, List(error)))</code></p>

<p>The <code>Ok</code> branch has the valid output.</p>

<p>The <code>Error</code> branch has a tuple <code>tuple(error, List(error))</code>.

The first value is the first error. The second value is a list with all errors (including the first).</p>

<h2>Custom property validator</h2>

<p>A property validator has two components:</p>

<ul>

<li>The error to return</li>

<li>A function that transforms the property if successful (<code>fn(input) -&gt; Option(output)</code>)</li>

</ul>

<p>Example:</p>

<pre><code class="language-rust">fn bigger_than_10(num: Int) -&gt; Option(num) {

  case num &gt; 10 {

    True -&gt;

      Some(num)

    False -&gt;

      None

  }

}



let custom = validator.custom(&quot;Must be bigger than 10&quot;, bigger_than_10)



let validator = fn(form: FormInput) {

  validator.build1(ValidForm)

  |&gt; validator.validate(form.quantity, custom)

}

</code></pre>

<h2>Test</h2>

<pre><code class="language-sh">rebar3 compile

rebar3 eunit

</code></pre>

<h2>Installation</h2>

<p>This package can be installed by adding <code>gleam_validator</code> to your <code>rebar.config</code> dependencies:</p>

<pre><code class="language-erlang">{deps, [

    gleam_validator

]}.

</code></pre>





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