Monthly Downloads: 13
Programming language: Haskell
License: BSD 3-clause "New" or "Revised" License
Tags: Web     Yesod    
Latest version: v0.9.2

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Yesod Comments

A drop-in comments module for a Yesod application.


# Stable
$ cabal install yesod-coments

# Development
$ git clone https://github.com/pbrisbin/yesod-comments
$ cd yesod-comments
$ cabal install


Make your foundation type an instance of YesodComments:

import Yesod.Comments

instance YesodComments MySite where
    -- Store comments using YesodPersist. It's the only backend 
    -- available at this time.
    commentStorage = persistStorage

    -- userDetails :: UserId -> Handler (Maybe UserDetails)
    -- This maps an AuthId m to more useful details like friendly name 
    -- and email address.
    userDetails = undefined

Next, add comments to some view somewhere. You only have to provide a unique thread identifier, and the widget will handle showing existing comments and a form for submitting new ones.

Note: Users must be authenticated to comment, therefore your site must be an instance of YesodAuth in order to use YesodComments.

-- addComments handles displaying the form on GET and processing it on 
-- POST, this follows the common Yesod idiom of handling both methods 
-- with one handler:

getPostR :: String -> Handler RepHtml
getPostR slug = do
    post <- getPostBySlug slug

    defaultLayout $ do
        setTitle "A post"

            <div .content>
                #{postContent post}

            <div .comments>
                #{addComments slug}

postPostR :: String -> Handler RepHtml
postPostR = getPostR

Finally, add a migrateComments call to your Application runner.

makeFoundation :: AppConfig DefaultEnv () -> Logger -> IO MySite
makeFoundation conf setLogger = do
    -- ...
    Database.Persist.Store.runPool dbconf (runMigration migrateComments) p
    return $ MySite conf setLogger s p manager dbconf


An administration subsite is provided to allow users to edit and delete comments they've left themselves. Any additional moderation must be done manually (for now).

Add the subsite to your routes:

/comments CommentsAdminR CommentsAdmin getCommentsAdmin

Optionally, define a few more functions in the YesodComments instance:

instance YesodComments MySite where
    -- ...

    -- How to get from a thread identifier to the page where it resides, 
    -- this is used to provide links back from the "my comments" page
    threadRoute = Just $ \thread -> PostR thread

    -- How to get to the subsite's Edit action for a comment
    editRoute = Just $ \thread cid -> CommentsAdminR $ EditCommentR thread cid

    -- How to get to the subsite's Delete action for a comment
    deleteRoute = Just $ \thread cid -> CommentsAdminR $ DeleteCommentR thread cid

With these defined, Edit and Delete links will appear whenever a user sees a comment they've left.


There is no styling provided by this library, but the markup is designed for Twitter's Bootstrap. If you use that, it should look OK out of the box. Even if you don't, the divs that Bootstrap requires should be more than adequate for creating your own styles.