---
title: "Running R in a Yesod application"
date: "2016-09-01"
output: html_document
---
```{r setup, include=FALSE}
knitr::knit_engines$set(pygmentize = function (options)
{
f = basename(tempfile("pygmentize", ".", ".txt"))
writeLines(options$code, f)
on.exit(unlink(f))
code = paste("-f html", options$engine.opts, f)
message("running: pygmentize ", code)
out = tryCatch(system2("pygmentize", code, stdout = TRUE, stderr = FALSE),
error = function(e) {
if (!options$error)
stop(e)
"Error in running pygmentize"
})
if (!options$error && !is.null(attr(out, "status")))
stop(paste(out, collapse = "\n"))
knitr::engine_output(options, options$code, out)
}
)
knitr::opts_chunk$set(engine="pygmentize", echo=FALSE, results="asis")
```
### Basic demo
This small app takes two numbers and returns their sum after performing the addition in R.
This is an Haskell app created with [Yesod](https://en.wikipedia.org/wiki/Yesod_(web_framework)), and R is called from Haskell with the help of the [inline-R](https://tweag.github.io/HaskellR/) package. You may take a look at my [inline-R demo](http://stla.github.io/stlapblog/posts/CallRinHaskell.html) and at my article [Hello Yesod+Ajax](http://stla.github.io/stlapblog/posts/HelloYesodAjax.html) before.
```{r, engine.opts="-l haskell"}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE PartialTypeSignatures #-}
{-# LANGUAGE OverloadedLists #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE QuasiQuotes #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE ViewPatterns #-}
{-# LANGUAGE OverloadedStrings, DeriveGeneric #-}
{-# LANGUAGE TypeFamilies #-}
import Yesod
import GHC.Generics
import qualified Language.R.Instance as R
import H.Prelude.Interactive
data HelloInlineR = HelloInlineR
mkYesod "HelloInlineR" [parseRoutes|
/ HomeR GET
/data DataR PUT
|]
instance Yesod HelloInlineR
data Args = Args {
_x :: Double,
_y :: Double
} deriving (Show,Generic)
instance FromJSON Args
getHomeR :: Handler ()
getHomeR = sendFile typeHtml "static/raddition.html"
runR :: Double -> Double -> IO(Double)
runR x y =
do
r <- [r|x_hs + y_hs|]
return $ (fromSomeSEXP r :: Double)
putDataR :: Handler String
putDataR = do
arguments <- requireJsonBody :: Handler Args
r <- liftIO $ runR (_x arguments) (_y arguments)
return $ show r
main :: IO ()
main = do
R.initialize R.defaultConfig
warp 3000 HelloInlineR
```
File *raddition.html*:
```{r, engine.opts="-l html"}
Enter two numbers:
```
Instead of requesting a html file, we can create its contents in the Haskell code:
```{r, engine.opts="-l haskell"}
...
import Yesod.Form.Jquery (YesodJquery (urlJqueryJs))
...
instance Yesod HelloInlineR
instance YesodJquery HelloInlineR
...
getHomeR :: Handler Html
getHomeR = defaultLayout $ do
setTitle "Yesod + Ajax"
getYesod >>= addScriptEither . urlJqueryJs
[whamlet|