do-list

Do notation for free.

Summary

do-list makes it easy to use do notation. You can construct lists or monoids using DoList or DoMonoid modules respectively. do-list is designed to work well with OverloadedStrings and OverloadedLists extensions. See examples.

As alternative there is a canonical Writer without overloading support.

Examples

Benchmarks

{-# LANGUAGE OverloadedLists #-}

module Main (main) where

import Criterion.Main
import Data.DoList (DoList, item, toList)

main :: IO ()
main = defaultMain $ toList $ do
  doBench "add"  $ whnf (2 +) (1 :: Int)
  doBench "sub" $ whnf (2 -) (1 :: Int)
  -- Regular criterion benchmarks are injected via list overloading
  [multBench, divBench]

multBench, divBench :: Benchmark
multBench = bench "mult" $ whnf (2 *) (2 :: Int)
divBench = bench "div" $ whnf (2 `div`) (2 :: Int)

-- Now we can define benchmarks with do notation.
doBench :: String -> Benchmarkable -> DoList Benchmark
doBench name = item . bench name

Multiline Text

{-# LANGUAGE OverloadedStrings #-}
{-# OPTIONS_GHC -fno-warn-unused-do-bind #-}

module Main (main) where

import Data.DoMonoid (runDoM)
import Data.Text.IO as T (putStr)

main :: IO ()
main = T.putStr $ runDoM $ do
  -- Lines are combined using Text.append
  "fib 0 = 0\n"
  "fib 1 = 1\n"
  "fib n = fib (n-1) + fib (n-2)\n"

Indentation

{-# LANGUAGE OverloadedStrings #-}
{-# OPTIONS_GHC -fno-warn-unused-do-bind #-}

module Main (main) where

import Data.DoList (DoList, fromList, toList)
import Data.Text as T (Text, append, unlines)
import Data.Text.IO as T (putStr)

main :: IO ()
main = T.putStr $ T.unlines $ toList $ do
  "Here goes indented list:"
  indent $ do
    "1. Item 1"
    indent $ do
      "* Item a"
      "* Item b"
    "2. Item 2"
    "3. Item 3"

indent :: DoList Text -> DoList Text
-- fromList and toList are no-ops
indent = fromList . map (append "  ") . toList