Lucid

Clear to write, read and edit DSL for writing HTML

See Lucid.Html5 for a complete list of Html5 combinators. That module is re-exported from this module for your convenience.

See Lucid.Base for lower level functions like makeElement, makeAttributes, termRaw, etc.

To convert html to the lucid DSL, use the (experimental) program lucid-from-html which may eventually be integrated into lucid itself.

Intro

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

p_, class_, table_, style_

Note: If you're testing in the REPL you need to add a type annotation to indicate that you want HTML. In normal code your top-level declaration signatures handle that.

For GHCi:

:set -XOverloadedStrings -XExtendedDefaultRules@
import Lucid

In a module: {-# LANGUAGE OverloadedStrings, ExtendedDefaultRules #-}

Plain text is written like this, and is automatically escaped:

>>> "123 < 456" :: Html ()
123 &lt; 456

Except some elements, like script_:

>>> script_ "alert('Hello!' > 12)" :: Html ()
<script>alert('Hello!' > 12)</script>

Elements nest by function application:

>>> table_ (tr_ (td_ (p_ "Hello, World!"))) :: Html ()
<table><tr><td><p>Hello, World!</p></td></tr></table>

Elements are juxtaposed via monoidal append (remember to import Data.Monoid):

>>> p_ "hello" <> p_ "sup" :: Html ()
<p>hello</p><p>sup</p>

Or monadic sequencing:

>>> div_ (do p_ "hello"; p_ "sup") :: Html ()
<div><p>hello</p><p>sup</p></div>

Attributes are set by providing an argument list:

>>> p_ [class_ "brand"] "Lucid Inc" :: Html ()
<p class="brand">Lucid Inc</p>

>>> p_ [data_ "zot" "foo",checked_] "Go!" :: Html ()
<p data-zot="foo" checked>go</p>

Attribute and element terms are not conflicting:

>>> style_ [style_ "inception"] "Go deeper." :: Html ()
<style style="inception">Go deeper.</style>

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!"))

Elements (and some attributes) are variadic and overloaded, see the Term class for more explanation about that.

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

>>> renderText (p_ "Hello!")
> "<p>Hello!</p>"

>>> 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.

renderText :: Html a -> Text

Render the HTML to a lazy Text.

This is a convenience function defined in terms of execHtmlT, runIdentity and toLazyByteString, and decodeUtf8. Check the source if you're interested in the lower-level behaviour.

renderBS :: Html a -> ByteString

Render the HTML to a lazy ByteString.

This is a convenience function defined in terms of execHtmlT, runIdentity and toLazyByteString. Check the source if you're interested in the lower-level behaviour.

renderTextT :: Monad m => HtmlT m a -> m Text

Render the HTML to a lazy Text, but in a monad.

This is a convenience function defined in terms of execHtmlT and toLazyByteString, and decodeUtf8. Check the source if you're interested in the lower-level behaviour.

renderBST :: Monad m => HtmlT m a -> m ByteString

Render the HTML to a lazy ByteString, but in a monad.

This is a convenience function defined in terms of execHtmlT and toLazyByteString. Check the source if you're interested in the lower-level behaviour.

renderToFile :: FilePath -> Html a -> IO ()

Render the HTML to a lazy ByteString.

This is a convenience function defined in terms of execHtmlT, runIdentity and toLazyByteString. Check the source if you're interested in the lower-level behaviour.

Running

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

execHtmlT

Arguments

:: Monad m

=> HtmlT m a

The HTML to generate.

-> m Builder

The a is discarded.

Build the HTML. Analogous to execState.

You might want to use this is if you want to do something with the raw Builder. Otherwise for simple cases you can just use renderText or renderBS.

evalHtmlT

Arguments

:: Monad m

=> HtmlT m a

HTML monad to evaluate.

-> m a

Ignore the HTML output and just return the value.

Evaluate the HTML to its return value. Analogous to evalState.

Use this if you want to ignore the HTML output of an action completely and just get the result.

For using with the Html type, you'll need runIdentity e.g.

>>> runIdentity (evalHtmlT (p_ "Hello!"))
()

runHtmlT :: Monad m => HtmlT m a -> m (Builder, a)

Run the HtmlT transformer.

Types

type Html = HtmlT Identity

Simple HTML builder type. Defined in terms of HtmlT. Check out that type for instance information.

Simple use-cases will just use this type. But if you want to transformer over Reader or something, you can go and use HtmlT.

data HtmlT m a

A monad transformer that generates HTML. Use the simpler Html type if you don't want to transform over some other monad.

Instances

MonadTrans HtmlT

Defined in Lucid.Base

Methods

lift :: Monad m => m a -> HtmlT m a

MonadReader r m => MonadReader r (HtmlT m)

Since: 2.9.7

Defined in Lucid.Base

Methods

ask :: HtmlT m r

local :: (r -> r) -> HtmlT m a -> HtmlT m a

reader :: (r -> a) -> HtmlT m a

MonadState s m => MonadState s (HtmlT m)

Since: 2.9.7

Defined in Lucid.Base

Methods

get :: HtmlT m s

put :: s -> HtmlT m ()

state :: (s -> (a, s)) -> HtmlT m a

(Monad m, a ~ ()) => TermRaw Text (HtmlT m a)

Given children immediately, just use that and expect no attributes.

Defined in Lucid.Base

Methods

termRaw :: Text -> Text -> HtmlT m a

MonadFix m => MonadFix (HtmlT m)

Defined in Lucid.Base

Methods

mfix :: (a -> HtmlT m a) -> HtmlT m a

MonadIO m => MonadIO (HtmlT m)

If you want to use IO in your HTML generation.

Defined in Lucid.Base

Methods

liftIO :: IO a -> HtmlT m a

Monad m => Applicative (HtmlT m)

Defined in Lucid.Base

Methods

pure :: a -> HtmlT m a

(<*>) :: HtmlT m (a -> b) -> HtmlT m a -> HtmlT m b

liftA2 :: (a -> b -> c) -> HtmlT m a -> HtmlT m b -> HtmlT m c

(*>) :: HtmlT m a -> HtmlT m b -> HtmlT m b

(<*) :: HtmlT m a -> HtmlT m b -> HtmlT m a

Functor m => Functor (HtmlT m)

Defined in Lucid.Base

Methods

fmap :: (a -> b) -> HtmlT m a -> HtmlT m b

(<$) :: a -> HtmlT m b -> HtmlT m a

Monad m => Monad (HtmlT m)

Defined in Lucid.Base

Methods

(>>=) :: HtmlT m a -> (a -> HtmlT m b) -> HtmlT m b

(>>) :: HtmlT m a -> HtmlT m b -> HtmlT m b

return :: a -> HtmlT m a

(Monad m, f ~ HtmlT m a) => Term [Attributes] (f -> HtmlT m a)

Given attributes, expect more child input.

Defined in Lucid.Base

Methods

term :: Text -> [Attributes] -> f -> HtmlT m a

(Monad m, ToHtml f, a ~ ()) => TermRaw [Attributes] (f -> HtmlT m a)

Given attributes, expect more child input.

Defined in Lucid.Base

Methods

termRaw :: Text -> [Attributes] -> f -> HtmlT m a

(Monad m, a ~ ()) => IsString (HtmlT m a)

We pack it via string. Could possibly encode straight into a builder. That might be faster.

Defined in Lucid.Base

Methods

fromString :: String -> HtmlT m a

(a ~ (), Monad m) => Monoid (HtmlT m a)

Monoid is right-associative, a la the Builder in it.

Defined in Lucid.Base

Methods

mempty :: HtmlT m a

mappend :: HtmlT m a -> HtmlT m a -> HtmlT m a

mconcat :: [HtmlT m a] -> HtmlT m a

(a ~ (), Monad m) => Semigroup (HtmlT m a)

Since: 2.9.7

Defined in Lucid.Base

Methods

(<>) :: HtmlT m a -> HtmlT m a -> HtmlT m a

sconcat :: NonEmpty (HtmlT m a) -> HtmlT m a

stimes :: Integral b => b -> HtmlT m a -> HtmlT m a

m ~ Identity => Show (HtmlT m a)

Just calls renderText.

Defined in Lucid.Base

Methods

showsPrec :: Int -> HtmlT m a -> ShowS

show :: HtmlT m a -> String

showList :: [HtmlT m a] -> ShowS

(a ~ (), m ~ Identity) => ToHtml (HtmlT m a)

Since: 2.9.8

Defined in Lucid.Base

Methods

toHtml :: forall (m0 :: Type -> Type). Monad m0 => HtmlT m a -> HtmlT m0 ()

toHtmlRaw :: forall (m0 :: Type -> Type). Monad m0 => HtmlT m a -> HtmlT m0 ()

Monad m => Term (HtmlT m a) (HtmlT m a)

Given children immediately, just use that and expect no attributes.

Defined in Lucid.Base

Methods

term :: Text -> HtmlT m a -> HtmlT m a

data Attributes

A list of attributes.

Instances

Monoid Attributes

Defined in Lucid.Base

Methods

mempty :: Attributes

mappend :: Attributes -> Attributes -> Attributes

mconcat :: [Attributes] -> Attributes

Semigroup Attributes

Defined in Lucid.Base

Methods

(<>) :: Attributes -> Attributes -> Attributes

sconcat :: NonEmpty Attributes -> Attributes

stimes :: Integral b => b -> Attributes -> Attributes

Term Text Attributes

Some terms (like style_, title_) can be used for attributes as well as elements.

Defined in Lucid.Base

Methods

term :: Text -> Text -> Attributes

TermRaw Text Attributes

Some termRaws (like style_, title_) can be used for attributes as well as elements.

Defined in Lucid.Base

Methods

termRaw :: Text -> Text -> Attributes

(Monad m, f ~ HtmlT m a) => Term [Attributes] (f -> HtmlT m a)

Given attributes, expect more child input.

Defined in Lucid.Base

Methods

term :: Text -> [Attributes] -> f -> HtmlT m a

(Monad m, ToHtml f, a ~ ()) => TermRaw [Attributes] (f -> HtmlT m a)

Given attributes, expect more child input.

Defined in Lucid.Base

Methods

termRaw :: Text -> [Attributes] -> f -> HtmlT m a

Classes

To support convenient use of HTML terms, HTML terms are overloaded. Here are the following types possible for an element term accepting attributes and/or children:

p_ :: Term arg result => arg -> result
p_ :: Monad m => [Attributes] -> HtmlT m () -> HtmlT m ()
p_ :: Monad m => HtmlT m () -> HtmlT m ()

The first is the generic form. The latter two are the possible types for an element.

Elements that accept no content are always concrete:

input_ :: Monad m => [Attributes] -> HtmlT m ()

And some elements share the same name as attributes, so you can also overload them as attributes:

style_ :: TermRaw arg result => arg -> result
style_ :: Monad m => [Attributes] -> Text -> HtmlT m ()
style_ :: Monad m => Text -> HtmlT m ()
style_ :: Text -> Attributes

class Term arg result | result -> arg where

Used to construct HTML terms.

Simplest use: p_ = term "p" yields p_.

Very overloaded for three cases:

• The first case is the basic arg of [(Text,Text)] which will return a function that wants children.
• The second is an arg which is HtmlT m (), in which case the term accepts no attributes and just the children are used for the element.
• Finally, this is also used for overloaded attributes, like style_ or title_. If a return type of (Text,Text) is inferred then an attribute will be made.

The instances look intimidating but actually the constraints make it very general so that type inference works well even in the presence of things like OverloadedLists and such.

Methods

term

Arguments

:: Text

Name of the element or attribute.

-> arg

Either an attribute list or children.

-> result

Result: either an element or an attribute.

Used for constructing elements e.g. term "p" yields p_.

Instances

Term Text Attributes

Some terms (like style_, title_) can be used for attributes as well as elements.

Defined in Lucid.Base

Methods

term :: Text -> Text -> Attributes

(Monad m, f ~ HtmlT m a) => Term [Attributes] (f -> HtmlT m a)

Given attributes, expect more child input.

Defined in Lucid.Base

Methods

term :: Text -> [Attributes] -> f -> HtmlT m a

Monad m => Term (HtmlT m a) (HtmlT m a)

Given children immediately, just use that and expect no attributes.

Defined in Lucid.Base

Methods

term :: Text -> HtmlT m a -> HtmlT m a

class ToHtml a where

Can be converted to HTML.

Methods

toHtml :: Monad m => a -> HtmlT m ()

Convert to HTML, doing HTML escaping.

toHtmlRaw :: Monad m => a -> HtmlT m ()

Convert to HTML without any escaping.

Instances

ToHtml ByteString

This instance requires the ByteString to contain UTF-8 encoded text, for the toHtml method. The toHtmlRaw method doesn't care, but the overall HTML rendering methods in this module assume UTF-8.

Since: 2.9.5

Defined in Lucid.Base

Methods

toHtml :: forall (m :: Type -> Type). Monad m => ByteString -> HtmlT m ()

toHtmlRaw :: forall (m :: Type -> Type). Monad m => ByteString -> HtmlT m ()

ToHtml ByteString

This instance requires the ByteString to contain UTF-8 encoded text, for the toHtml method. The toHtmlRaw method doesn't care, but the overall HTML rendering methods in this module assume UTF-8.

Since: 2.9.5

Defined in Lucid.Base

Methods

toHtml :: forall (m :: Type -> Type). Monad m => ByteString -> HtmlT m ()

toHtmlRaw :: forall (m :: Type -> Type). Monad m => ByteString -> HtmlT m ()

ToHtml Text

Defined in Lucid.Base

Methods

toHtml :: forall (m :: Type -> Type). Monad m => Text -> HtmlT m ()

toHtmlRaw :: forall (m :: Type -> Type). Monad m => Text -> HtmlT m ()

ToHtml Text

Defined in Lucid.Base

Methods

toHtml :: forall (m :: Type -> Type). Monad m => Text -> HtmlT m ()

toHtmlRaw :: forall (m :: Type -> Type). Monad m => Text -> HtmlT m ()

ToHtml String

Defined in Lucid.Base

Methods

toHtml :: forall (m :: Type -> Type). Monad m => String -> HtmlT m ()

toHtmlRaw :: forall (m :: Type -> Type). Monad m => String -> HtmlT m ()

(a ~ (), m ~ Identity) => ToHtml (HtmlT m a)

Since: 2.9.8

Defined in Lucid.Base

Methods

toHtml :: forall (m0 :: Type -> Type). Monad m0 => HtmlT m a -> HtmlT m0 ()

toHtmlRaw :: forall (m0 :: Type -> Type). Monad m0 => HtmlT m a -> HtmlT m0 ()

Re-exports

module Lucid.Html5