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Select provides flexible building blocks for selection interfaces in Halogen. If you need a dropdown menu, typeahead, autocomplete, multi-select, calendar, image picker, or other selection interface, and you want it to be accessible, and you also want complete visual control over the component, then you're in the right place.

This library is under active development and changes often. If you need a stable selection library, we're not there yet! Please consider helping out with a pull request to add features you need and help us reach 1.0!

There are a few ways to get started with the Select library.

Select is available on Bower and Pursuit:

bower i --save purescript-halogen-select

You can see working examples of components built using this library in a few places:

Have an example of a component you've built with Select? Open a PR or drop us a message and we can help review and showcase your work.

To build the documentation site locally:

  1. Download the static site builder Gutenberg
  2. Build the static html with npm run -s build-site
  3. Build the PureScript with npm run -s build-docs
  4. Open the index.html file in docs/dist

The library provides essential behaviors for selection user interfaces as a group of Halogen components. But you won't find a single render function in the code. Instead, with the help of a few setProps helpers, you can write your HTML rendering however you'd like. You can freely include your own queries and the library will return them to be run. You can even use any data you want from your parent state in your render functions. The library manages user interaction, state, accessibility, and logic; you are responsible for rendering HTML depending on that state.

  1. Provide behaviors, not styles
    Developers should be able to style and display dropdowns and typeaheads however they would like, rather than be forced to use particular CSS classes or re-implement the component with their HTML. This is accomplished with augmented render functions as described below. We provide the machinery; you provide the HTML and styles.

  2. Export the building blocks, not just the end result
    Developers should be able to take a core set of behaviors and choose how they would like to handle them in their own version of the component. If you would like the typeahead's functionality but do something fancy with the selected items, you should be able to. Each building block is exported.

  3. Require minimal configuration
    Instantiating a typeahead shouldn't require a 50-field configuration record. We require at minimum two things: the data to populate the menu and the HTML to render that data. The rest is taken care of by the component. You are responsible for handling two things: when an item was selected, and when the user has performed a new search. If you want to do even less, you can use one of our default implementations to drop in to your project.

  4. Be accessible (Upcoming)
    ARIA props and other features necessary for accessibility online should be handled properly without any setup.

The primary design decision made in this project vs. other typeaheads is offloading HTML rendering to the user. Rather than render an input field ourselves and provide a CSS class for styling, we allow you to write your own HTML and augment your properties with the behaviors we need for the select to function.

In practice, you are responsible for providing render functions for each HTML element involved in the component. Your render function should be augmented using one of our provided functions, which will extend your CSS & events with our behaviors.

For example, you can make your container compatible with the component with the getContainerProps function, which you would apply to the array of iprops present on your button element:

[ ... your HTML ...
, HH.span
    ( setContainerProps [ ... your css & events ... ] ) -- Augments your props with our behaviors
    [ ... your HTML ... ]
, ... your HTML ...

Warning: If your events are duplicated by ours, they will be overwritten and fail to trigger.

Most of the time Halogen queries look like this:

data QueryF (… other type arguments omitted …) a
  = ...
  | SetVisibility Visibility a
  | GetVisibility (Visibility -> a)

(where QueryF is used directly as the Halogen query functor)

This library takes a slightly different approach: the query functor is actually Control.Monad.Free.Free QueryF, the free monad generated by the query functor.

This allows queries the full power of monadic (and applicative) composition: sequencing effects, determining control flow based on previous results, and my favorite: doing nothing (pure unit).

We now define smart query constructors for this Free pattern like so:

-- | Set the container visibility (`On` or `Off`).
setVisibility ::  o item eff. Visibility -> Query o item eff Unit
setVisibility v = liftF (SetVisibility v unit)

-- | Get the container visibility (`On` or `Off`). Most useful when sequenced
-- | with other actions.
getVisibility ::  o item eff. Query o item eff Visibility
getVisibility = liftF (GetVisibility id)

Different patterns

In the simple cases, the helpers Halogen use to work with raw query constructors are folded into the smart Free query constructors already: H.action (SetVisibility On) becomes simply setVisiblity On, and similarly H.request GetVisibility is just getVisibility. This is because these patterns are typically present already smart constructors: setVisibility returns Free QueryF Unit, since it is an action, and getVisibility returns Free QueryF Visibility, since it requests the visibility. This allows for easy composition in do notation:

toggleVisibility = do
  vis <- getVisibility
  setVisibility (not vis)

C’est très facile!

Event handlers look a little different. This is one example:

HE.onMouseDown \ev -> Just do
    Select.preventClick ev index
    when doBlur Select.triggerBlur

(Of course you may return Nothing if you so wish, but its effect is just like pure unit now.)

If you do not need access to the argument ev, Select.always provides a simple shortcut for const <<< Just:

HE.onMouseOver $ Select.always $ Select.highlight (Index index)

Returning non-unit values

Use map or <$ or pure to return other types of values from a query. So, instead of something like this:

H.subscribe $ eventSource' someEventSource
  \value -> Just (SetVisibility value H.Listening)


H.subscribe $ eventSource' someEventSource
  \value -> Just $ setVisibility value $> H.Listening


H.subscribe $ eventSource' someEventSource
  \value -> Just do
    setVisibility value
    pure H.Listening

Inspiration & Thanks

This project drew inspiration from the approach taken by paypal/downshift. Special thanks to Nathan Faubion and Nicholas Scheel for their help.