The new runtime Hamlet API

September 18, 2015

GravatarBy Michael Snoyman

The Hamlet HTML templating system is, by default, parsed at compile time, allowing it to do quite a bit of static checking. But it can also be useful to parse these templates at runtime, such as if you wanted to allow dynamic content to be submitted by users.

A few weeks ago, a discussion on Reddit pointed out that the API for runtime Hamlet in shakespeare was pretty bad. Just a week later, I came up with a use case for runtime Hamlet myself, and decided to put together a new, more user friendly API.

This new API is provided in Text.Hamlet.Runtime. Hopefully it's much easier to follow going on here. And this time, there are even comments on the functions! I'm including the example from the module below to give a better feel for how this works:

{-# LANGUAGE OverloadedStrings #-}
import Text.Hamlet.Runtime
import qualified Data.Map as Map
import Text.Blaze.Html.Renderer.String (renderHtml)

main :: IO ()
main = do
    template <- parseHamletTemplate defaultHamletSettings $ unlines
        [ "<p>Hello, #{name}"
        , "$if hungry"
        , "  <p>Available food:"
        , "  <ul>"
        , "    $forall food <- foods"
        , "      <li>#{food}"
    let hamletDataMap = Map.fromList
            [ ("name", "Michael")
            , ("hungry", toHamletData True) -- always True
            , ("foods", toHamletData
                [ "Apples"
                , "Bananas"
                , "Carrots"
    html <- renderHamletTemplate template hamletDataMap
    putStrLn $ renderHtml html


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