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