138 lines
3.2 KiB
TeX
138 lines
3.2 KiB
TeX
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\documentclass[12pt]{beamer}
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\usetheme{metropolis}
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\usepackage{minted}
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\newenvironment{code}{\ttfamily}{\par}
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\title{servant}
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\subtitle{Defining web APIs at the type-level}
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\begin{document}
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\metroset{titleformat frame=smallcaps}
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\setminted{fontsize=\scriptsize}
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\maketitle
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\section{Introduction}
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\begin{frame}{Type-level DSLs?}
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\begin{itemize}
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\item (Uninhabited) types with attached ``meaning''
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\item The Expression Problem (Wadler 1998)
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\item API representation and interpretation are separated
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\item APIs become first-class citizens
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\end{itemize}
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\end{frame}
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\begin{frame}{Haskell extensions}
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\begin{itemize}
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\item TypeOperators
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\item DataKinds
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\item TypeFamilies
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\end{itemize}
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\end{frame}
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\begin{frame}[fragile]{A servant example}
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\begin{minted}{haskell}
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type PubAPI = "pubs" :> Get ’[JSON] [Pub]
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:<|> "pubs" :> "tagged"
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:> Capture "tag" Text
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:> Get ’[JSON] [Pub]
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\end{minted}
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\end{frame}
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\begin{frame}[fragile]{Computed types}
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\begin{minted}{haskell}
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type TaggedPubs = "tagged" :> Capture "tag" Text :> ...
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taggedPubsHandler :: Server TaggedPubs
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taggedPubsHandler tag = ...
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\end{minted}
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\end{frame}
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\begin{frame}[fragile]{Computed types}
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\begin{minted}{haskell}
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type TaggedPubs = "tagged" :> Capture "tag" Text :> ...
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taggedPubsHandler :: Server TaggedPubs
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taggedPubsHandler tag = ...
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Server TaggedPubs ~
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Text -> EitherT ServantErr IO [Pub]
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\end{minted}
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\end{frame}
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\section{Interpretations}
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\begin{frame}{servant-server}
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The one everyone is interested in!
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\begin{itemize}
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\item Based on WAI, can run on warp
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\item Interprets combinators with a simple \texttt{HasServer c} class
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\item Easy to use!
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\end{itemize}
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\end{frame}
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\begin{frame}[fragile]{HasServer ...}
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\begin{minted}{haskell}
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instance (KnownSymbol path, HasServer sublayout)
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=> HasServer (path :> sublayout) where
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type ServerT (path :> sublayout) m = ServerT sublayout m
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route ...
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where
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pathString = symbolVal (Proxy :: Proxy path)
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\end{minted}
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\end{frame}
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\begin{frame}[fragile]{Server example}
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\begin{minted}{haskell}
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type Echo = Capture "echo" Text :> Get ’[PlainText] Text
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echoAPI :: Proxy Echo
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echoAPI = Proxy
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echoServer :: Server Echo
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echoServer = return
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\end{minted}
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\end{frame}
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\begin{frame}{servant-client}
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\begin{itemize}
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\item Generates Haskell client functions for API
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\item Same types as API specification: For RPC the whole ``web layer'' is abstracted away
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\item Also easy to use!
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\end{itemize}
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\end{frame}
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\begin{frame}{servant-docs, servant-js ...}
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Many other interpretations exist already, for example:
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\begin{itemize}
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\item Documentation generation
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\item Foreign function export (e.g. Elm, JavaScript)
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\item Mock-server generation
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\end{itemize}
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\end{frame}
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\section{Demo}
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\section{Conclusion}
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\begin{frame}{Drawbacks}
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\begin{itemize}
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\item Haskell has no custom open kinds (yet)
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\item Proxies are ugly
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\item Errors can be a bit daunting
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\end{itemize}
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\end{frame}
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\begin{frame}{Questions?}
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Ølkartet: github.com/tazjin/pubkartet \\
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Slides: github.com/tazjin/servant-presentation
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@tazjin
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\end{frame}
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\end{document}
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