buggymcbugfix

{-# LANGUAGE DeriveFoldable, DeriveFunctor #-}
{-# LANGUAGE InstanceSigs #-}
{-# LANGUAGE LambdaCase #-}

import Data.Foldable (toList)
import Data.List (nub)
import Data.Map (Map)
import qualified Data.Map as Map
import Data.Maybe (listToMaybe)
import Data.Monoid

buggymcbugfix

#! /usr/bin/env stack
-- stack --resolver lts-9.14 --install-ghc script --package base

import Data.Maybe (mapMaybe)
import System.Environment (getArgs)
import Text.Read (readMaybe)

{- USAGE

Pipe input:

buggymcbugfix

import Data.Monoid

data List a = List | List a :• a

xs • x = xs :• x
infixl •

instance Show a => Show (List a) where
  show List = "List"
  show (xs :• x) = show xs ++ " •" ++ show x

buggymcbugfix

Unix tree in Haskell

My take on pretty printing a rose tree like the unix tree command does. Inspired by this blog post of a version in OCaml.

It is pure and idiomatic without using any library functions. Thanks to laziness, it doesn't wait to return until the whole string is built. As such it will print a finite prefix of large or infinite trees (see example below).

buggymcbugfix

Catch-all considered harmful?

I have been thinking about a potential source of bugs from catch-all pattern matches and would like to know your thoughts.

Motivation

Totality is usually a desirable property of a function and the catch-all can conveniently buy us totality. But at what price?

I have been indoctrinated that rigour goes above convenience (think along the lines of: "Once we indulge in the impurities of I/O, there is no redemption.")

I would like to evaluate the trade-offs between convenience for the programmer and a potential source of bugs.

buggymcbugfix

-- Effectful example in Gram

-- Similar to Haskell
-- main :: IO a
-- main = readLn

echo : (Int -> <Int> {}) -> Int -> <Int> {W}
echo = \f -> \x -> let <a : Int> = write x in f x

dub : Int -> <Int> {}

buggymcbugfix

import Data.Char(toUpper)

main = do
  inpStr <- readFile "test.txt"
  writeFile "output.txt" (map toUpper inpStr)

buggymcbugfix

#! /usr/bin/env stack
-- stack --resolver lts-8.15 --install-ghc script --package base
{-# LANGUAGE ScopedTypeVariables #-}

-- Usage:
--   $ echo -e "1.2 3.4\n5.6 not-a-number" | ./total.hs
--   10.2

import Data.Maybe (mapMaybe)
import Text.Read (readMaybe)