Motivation

Recently I migrated the vpn-router frontend to Miso, I noticed that DOM functions (e.g. div_) accept CSS class names as plain strings. This prevents GHC from catching typos in referenced names, even if stylesheets are correct and defined with clay.

Usage

The library leverages the power of TH to parse CSS snippets from quasi quotes or style files and to define Haskell constants for every class mentioned in the input.

Quasi-quote input

{-# LANGUAGE QuasiQuotes #-}
module Css where
import CssClassBindings ( css )
[css|
.foo-bar {
  color: #fc2c2c;
}
#foo-bar {
  color: #fc2c2c;
}
|]

module Main where
import Css (fooBar, FooBar(..), cssAsLiteralText)
import CssClassBindings qualified as C
import Miso
import Miso.Html.Element (div_, button_)
import Miso.Html.Property qualified as P
class_ :: C.CssClass MisoString -> Attribute action
class_ = P.class_ . C.class_
key_ :: C.CssIdentifier i => i -> Attribute action
key_ = P.key_ . C.id_
app :: App Model Action
app = (component emptyModel updateModel viewModel)
  { styles = [ Style cssAsLiteralText ]
  }
viewModel :: Model -> View Model Action
viewModel m =
  div_ []
    [ button_
      [ key_ FooBar
      , class_ fooBar
      ]
      [ "Submit" ]
    ]

The library has been created to improve a miso-based app, but it does not depend on miso and it can be used in other setups.

fooBar :: IsString s => CssClass s
cssAsLiteralText :: IsString s => s

File input

{-# LANGUAGE TemplateHaskell #-}
module Css where
import CssClassBindings ( includeCss )
includeCss "assets/style.css"

module Main where
import Css (fooBar, FooBar(..), style)
-- ...

Development environment

HLS should be available inside the default dev shell.

$ nix develop
$ emacs src/*/*/Qq.hs &
$ cabal build