@hackage lucid2.11.20250303

Clear to write, read and edit DSL for HTML

lucid Hackage Build Status

Clear to write, read and edit DSL for writing HTML

Table of Contents

Introduction

HTML terms in Lucid are written with a postfix ‘_’ to indicate data rather than code. Some examples:

p_, class_, table_, style_

See Lucid.Html5 for a complete list of Html5 combinators.

Plain text is written using the OverloadedStrings and ExtendedDefaultRules extensions, and is automatically escaped:

λ> "123 < 456" :: Html ()

123 &lt; 456

Elements nest by function application:

λ> table_ (tr_ (td_ (p_ "Hello, World!"))) :: Html ()

<table><tr><td><p>Hello, World!</p></td></tr></table>

Elements are juxtaposed via monoidal append:

λ> p_ "hello" <> p_ "sup" :: Html ()

<p>hello</p><p>sup</p>

Or monadic sequencing:

λ> div_ (do p_ "hello"; p_ "sup") :: Html ()

<div><p>hello</p><p>sup</p></div>

Attributes are set by providing an argument list:

λ> p_ [class_ "brand"] "Lucid Inc" :: Html ()

<p class="brand">Lucid Inc</p>

Here is a fuller example of Lucid:

table_ [rows_ "2"]
       (tr_ (do td_ [class_ "top",colspan_ "2",style_ "color:red"]
                    (p_ "Hello, attributes!")
                td_ "yay!"))

<table rows="2">
  <tr>
    <td style="color:red" colspan="2" class="top">
      <p>Hello, attributes!</p>
    </td>
    <td>yay!</td>
  </tr>
</table>

Rendering

For proper rendering you can easily run some HTML immediately with:

λ> renderText (p_ "Hello!")

"<p>Hello!</p>"

Or to bytes:

λ> renderBS (p_ [style_ "color:red"] "Hello!")

"<p style=\"color:red\">Hello!</p>"

For ease of use in GHCi, there is a Show instance, as demonstrated above.

If the above rendering functions aren't suited for your purpose, you can run the monad directly via execHtml and use the more low-level blaze Builder, which has a plethora of output modes in Blaze.ByteString.Builder.

See the documentation for the Lucid module for information about using it as a monad transformer.

Good to know

  • Attributes are escaped, so you cannot write arbitrary JavaScript in attributes. Instead, do something like onclick_ "foo()".
  • Attributes are rendered in the order that they are written in your Haskell code.

Transforming

You can use lift to call parent monads.

λ> runReader (renderTextT (html_ (body_ (do name <- lift ask
                                            p_ [class_ "name"] (toHtml name)))))
             ("Chris" :: String)

"<html><body><p class=\"name\">Chris</p></body></html>"