Haskell web framework (because Scotty had trouble yodeling) https://github.com/mcschroeder/welshy

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MIT licensed by Michael Schröder
Maintained by mcschroeder@gmail.com

A Haskell web framework heavily influenced by the excellent Scotty, which was in turn influenced by Ruby's Sinatra.

Welshy strives to make it easier to do error handling without overly complicating the control flow. An example:

{-# LANGUAGE OverloadedStrings #-}
import Control.Applicative
import Control.Monad
import qualified Data.Text.Lazy as T
import Network.HTTP.Types
import Web.Welshy

fibs :: [Int]
fibs = 0 : 1 : zipWith (+) fibs (tail fibs)

main :: IO ()
main = welshy 3000 $ do
    get "/fibs" $ do
        offset <- queryParam "offset" <|> return 0
        length <- queryParam "length"

        when (offset < 0 || length < 0)
             (halt $ status badRequest400)

        when (offset + length > 1000)
             (halt $ status requestedRangeNotSatisfiable416)

        let result = take length $ drop offset fibs
        text $ T.pack $ show result

Some of the features demonstrated here:

  • You can halt the current action at any point and continue with a different one.

  • Functions like queryParam and jsonParam have built-in error handling.

  • Welshy's Action monad is an instance of Alternative.

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