Talk given at Kats Conf 2015

1. Introduction to Yesod
@bobjlong - Kats Conf 2015, Dublin

2. Brief overview + concepts
Composition
Builds and deployments

3. About me
twitter.com/bobjlong
github.com/bobjflong

4. Web development
Professional history of Rails
Late-night Haskell enthusiast

5. Haskell web dev

6. Rich types
Performance
Joy of discovery
Libraries
Error class elimination

7. Everyday problems

8. Wiring
Encoding issues
Safety (XSS)
Performance, concurrency

9. What is Yesod?

10. “Turn runtime bugs into compile-time errors”
http://www.yesodweb.com

11. “A developer should be able to continue to
productively write code as their application
grows and more team members join.”
“The key to achieving this is applying
Haskell's type-safety to an otherwise
traditional MVC REST web framework.”
http://www.yesodweb.com/page/about

12. Introducting Yesod
✨Concepts✨

13. Routing & Handlers
DSLs
Composability
“Persistent”
- a safe and productive query interface
Familiarity
- conventions + scaffolding

14. {-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE QuasiQuotes #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}
import Yesod
data HelloWorld = HelloWorld
mkYesod "HelloWorld" [parseRoutes|
/ HomeR GET
|]
instance Yesod HelloWorld
getHomeR :: Handler Html
getHomeR = defaultLayout [whamlet|Hello World!|]
main :: IO ()
main = warp 3000 HelloWorld
routing
handler
starting a web server

15. Composition

16. Case study: yesod-transloadit

17. Transloadit
a webservice for handling file uploads,
transformations, transcoding etc.

18. jQuery dependency
transloadit.js
server-side scripting to compute HMAC
client-side scripting to “attach” transloadit
server-side scripting to handle response from
Transloadit
where are client side assets loaded?

19. getHomeR :: Handler Html
getHomeR = defaultLayout $ do
let now = UTCTime (ModifiedJulianDay 50000) (secondsToDiffTime 10)
ident <- newIdent
let expiry = addUTCTime 3600 now
key = Key "my_key"
template = Template "my_template"
secret = Secret "my_secret"
params = mkParams expiry key template ident secret
sig <- either (const $ error "nooo") transloadIt params
t <- tokenText
[whamlet|
<form id="#{ident}" action=@{HomeR} method="POST">
<input type="hidden" name="_token" value="#{t}">
<input type="hidden" name="signature" value="#{sig}">
<input type="file" name="my_file">
<input type="submit" value="Upload">
|]
return ()

20. postHomeR :: Handler Html
postHomeR = defaultLayout $ do
results <- handleTransloadit
case nthStepResult 0 "cropped_thumb" results of
Just s -> [whamlet| <img src="#{s ^. sslUrl}"/> |]
_ -> [whamlet| No results :( |]
return ()

21. How?
github.com/bobjflong/yesod-transloadit
Yesod has a generic WidgetT type that works for
all web-apps
Typeclasses are used to enforce dependencies

22. transloadIt ::
(YesodJquery m, YesodTransloadit m) =>
TransloaditParams -> WidgetT m IO Signature

23. data Test = Test
instance Yesod Test
instance YesodJquery Test
instance YesodTransloadit Test
— or
instance YesodTransloadit Test where
transloaditRoot _ = “https://my_cdn.com/“

24. Persistent

25. share [mkPersist sqlSettings,
mkMigrate “migrateAll”]
[persistLowerCase|
Person
name String
age Int Maybe
deriving Show
BlogPost
title String
authorId PersonId
deriving Show
|]

26. johnId <- insert $ Person "John Doe" $ Just 35
oneJohnPost <- selectList
[BlogPostAuthorId ==. johnId]
[LimitTo 1]

27. esqueleto
“esqueleto is a bare bones, type-safe EDSL for SQL queries
that works with unmodified persistent SQL backends”
https://hackage.haskell.org/package/esqueleto

28. E.selectSource $ E.from $
(blog `E.InnerJoin` author) -> do
E.on $ blog ^. BlogAuthor E.==. author ^. AuthorId
return
( blog ^. BlogId
, blog ^. BlogTitle
, author ^. AuthorName
)

29. Building & deploying

30. Cabal
Stack
Nix

31. Quick intro to Nix

32. Reproducible, stable builds
Binaries
Complete dependency graphs

33. Immutable
Infrastructure

34. 1. Pre-bake an AMI with a Nix environment
2. Build a new AMI per app version with Nix
3. Associate new instances with the ASG
http://bobjflong.co/posts/2015-08-22-yesod.html

35. Questions?
@bobjlong
https://github.com/bitemyapp/learnhaskell
http://www.yesodweb.com/book