proglangbase / bbhw

Bye Bye Hello World

Bye Bye Hello World

Traditionally, the Hello World program is the first example offered as the introduction to a programming language and does nothing more than output the string "Hello World" to the output medium--generally the console. While adequate to demonstrate a particular language can actually do something, for anyone other than the novice programmer, a more thorough example is called for.

These code examples attempt to demonstrate basic capabilities of the languages we will examine by expanding Hello World to include:

• Command Line Parameters
  Taking input criteria from the command line.

• Prompted Input
  Prompting the user for input criteria.

• Input Validation
  Examination of input criteria against programmed limits.

• Conditional Branching
  Altering the execute path based on conditions.

• Iteration
  Repeated execution until a condition is met.

Usage

bbhw [count]

where: count = Number of iterations. User prompted of not supplied.

Result

Counts down from count to 0, pausing between each iteration, and prints each count until complete.

bbhw's Issues

Haskell bye bye hello world

Neat idea. Here's an example of abusing Haskell to write this program; being so IO centric, it only leaves the IO monad in a few spots, and I wrote most of it with do blocks.

#! /usr/bin/env runghc
-- Ignoring the shebang line above is a GHC extension 
-- (see 6.19.6. Whitespace)

-- LANGUAGE here is a pragma, not a comment!
{-# LANGUAGE Haskell2010, NumericUnderscores #-}
-- The NumericUnderscores extension is enabled by default in
-- GHC2021 or GHC2024, it got switched off by Haskell2010. 

-- GHC specific delay. 
-- There is no standard delay, and the POSIX ones may be interrupted.
import Control.Concurrent (threadDelay)

import Control.Monad (forM_)
import Numeric (readDec)
import System.Environment (getArgs)
import System.IO (stdout, hSetBuffering, BufferMode(NoBuffering))

-- Sequential do style; this program is heavily IO centric.
main = do
  let   -- could move these functions out of main
    ensureCount s = case readDec s of
      [(n,"")] -> return n
      _ -> do
        putStrLn ("Invalid countdown "++s++", try again...")
        demandCount
    demandCount = do
      putStr "Count? "
      s <- getLine
      ensureCount s
  args <- getArgs
  hSetBuffering stdout NoBuffering
  count <- case args of
    [arg] -> ensureCount arg
    _     -> demandCount
  putStr "World, Hello..."
  forM_ [count, count-1 .. 1] $ \i -> do
    putStr (show i ++ "...")
    threadDelay 1_000_000  -- Here are our two extensions.
  putStrLn "Bye Bye."

Contributing guidelines?

Hello!

I'd like to contribute a new language example, but I have some questions about contribution expectations:

• is it required to include the same Mozilla public license I'm seeing in the other examples?
• if the example can either be compiled or run more like a script, should both be reflected in the run file, or just the compilation route there while leaving a nice shebang on the source file, or what?
• if the compiler is not commonly packaged, should the run script download it, or instead download its source and compile the compiler itself?
• any other notes new contributors should be aware of before submitting a PR?

Thanks!