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Editorial Team
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Asked: 2026-06-15T09:05:12+00:00

Background : I am studying how Hamlet works, with WAI, but without Yesod. I

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Background: I am studying how Hamlet works, with WAI, but without Yesod. I have no grasp of Template Haskell, but before I dive into it, I am wondering if there is a known/quick solution for this task.

Specifics: I would like to know how to change the NewlineStyle in the context of a Hamlet quasiquote.

Exploration: I believe it has something to do with a function call that looks like this

hamletWithSettings 
htmlRules 
HamletSettings 
  {
      hamletDoctype             = "<!DOCTYPE html>"
     ,hamletNewlines            = DefaultNewlineStyle
     ,Hamlet.hamletCloseStyle   = htmlCloseStyle -- this fn is in a hidden module 
     ,Hamlet.hamletDoctypeNames = []
  }

… however, I don’t know how to write the code that does this, in the context of the quasiquote.

Here is the working code, which I hope to modify:

{-# LANGUAGE OverloadedStrings #-} 
{-# LANGUAGE QuasiQuotes #-}

import Control.Monad.Trans.Resource
import Text.Hamlet                                  as Hamlet
import qualified Data.ByteString.Lazy.Char8         as ByteString
import qualified Network.Wai                        as Wai
import qualified Network.HTTP.Types                 as Http
import qualified Network.Wai.Handler.Warp           as Warp
import qualified Text.Blaze                         as Blaze 
import qualified Text.Blaze.Html.Renderer.String    as Blaze
-------------------------------------------------------------------------------
main :: IO ()
main = Warp.run 3000 application
-------------------------------------------------------------------------------
application :: Wai.Request -> ResourceT IO Wai.Response
application request = return $
    case (head $ Wai.pathInfo request) of
        "html" ->   
            Wai.responseLBS Http.status200  []  $ ByteString.pack 
                                                $ Blaze.renderHtml 
                                                $ htmlDoc -- defined below
        "d3" ->     
            Wai.ResponseFile Http.status200 [] "./d3.v2.min.js" Nothing
        _ ->        
            Wai.responseLBS Http.status400  [] "" 
-------------------------------------------------------------------------------
htmlDoc :: Hamlet.Html
htmlDoc = [shamlet|
!!!
<html>
    <head>
        <title>Study Graph
        <!-- <link rel="stylesheet" type="text/css" href="/css"> -->
        <script type="text/javascript" src="/d3" />
        <style>
        <script>
            window.onload = function()
            {
                svg = 
                    d3  .select("body")
                        .append("svg")
                        .attr("width", "100%")
                        .attr("height", "100%")
                /* SOLUTION to strawman: a solitary "\" on this code row, will render a single newline character; i.e. "\n\\\n" renders as "\n" */
                svg .selectAll("circle")
                    .data([ {"cx": 1.0, "cy": 1.1, "r":1}, 
                            {"cx": 2.0, "cy": 2.5, "r":0.9} ])

            }
    <body>
|]
-------------------------------------------------------------------------------

Thanks in advance for any assistance, insults, or other commentary.

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1 Answer

  1. Editorial Team

    The basic idea would be to create a new identifier, e.g.:

    myHamlet = hamletWithSettings 
  htmlRules 
  (   HamletSettings 
    "<!DOCTYPE html>" 
    DefaultNewlineStyle htmlCloseStyle doctypeNames )

    Then use myHamlet in place of hamlet, e.g.:

    htmlDoc = [myHamlet|...|]

    Due to the stage restriction, you’ll likely need to declare myHamlet in a different module to the one where you use it.

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