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A minimum web dev DSL.

Note: loli is deprecated by miku.


import Network.Loli
import Hack.Handler.Happstack

main = run . loli $ get "/" (text "loli power")


cabal update
cabal install loli
cabal install hack-handler-happstack

-- copy and paste the above example to myapp.hs

ghc --make myapp.hs

check: http://localhost:3000

Quick reference



-- use - instead of $ for clarity
import MPS.Light ((-))
import Prelude hiding ((-))

import Network.Loli
import Hack.Handler.Happstack

main = run . loli - do

  get "/" - do
    -- something for a get request

  post "/" - do
    -- for a post request

  put "/" - do
    -- put ..

  delete "/" - do
    -- ..


get "/say/:user/:message" - do
  text . show =<< captures

-- /say/jinjing/hello will output
-- [("user","jinjing"),("message","hello")]


-- public serve, only allows `./src`
public (Just ".") ["/src"]

Mime types

-- treat .hs extension as text/plain
mime "hs" "text/plain"


-- before takes a function of type (Env -> IO Env)
before - \e -> do
  putStrLn "before called"
  return e

-- after takes that of type (Response -> IO Response)
after return

Hack integration

Use hack middleware

-- note both etag and lambda middleware are removed ... for somce ghc 7.0 compatability ><

import Hack.Contrib.Middleware.ETag
import Hack.Contrib.Middleware.Lambda

middleware etag
middleware lambda

Convert loli into a hack application

-- in Network.Loli.Engine

loli :: Unit -> Application


  • It's recommended to use your own html combinator / template engine, loli's template system is for completeness rather then usefulness... The author has removed the section on view from this readme. Examples can still be found in src/Test/Test.hs. Try DIY with, e.g. moe. The template code will stay for, say, a few years, but will eventually fade away.
  • Example view using custom html combinator (moe in this case)
  • When inspecting the request, use ask defined in ReaderT monad to get the Hack.Environment, then use helper method defined in Hack.Contrib.Request to query it.
  • Response is in StateT, html and text are simply helper methods that update the state, i.e. setting the response body, content-type, etc.
  • You do need to understand monad transformers to reach the full power of loli.
  • For mac users, use GHC 6.12.1 if you have trouble running the server.


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