---
title: Doppler
author: nbloomf
date: 2016-01-22
tags: literate-haskell, munge
---

I am feeling bored today. Let's make a thing so I don't have to keep looking up ANSI color codes.

> module Doppler where
> 
> import Data.Char (toLower)
> import System.IO
> import System.Environment (getArgs)
> import System.Exit (exitWith, exitSuccess, exitFailure)
> 
> main :: IO ()
> main = do
>   args <- getArgs
> 
>   case args of
>     {- foreground only -}
>     [fg] -> do
>       case colorize (fg, "null") of
>         Just x  -> putStr x
>         Nothing -> showUsage >> exitFailure
> 
>     {- foreground and background -}
>     [fg,bg] -> do
>       case colorize (fg,bg) of
>         Just x  -> putStr x
>         Nothing -> showUsage >> exitFailure
> 
>     {- ruh roh -}
>     _ -> showUsage >> exitFailure
> 
>   {- echo -}
>   getContents >>= putStr
> 
>   {- reset colors and intensity -}
>   putStr $ "\x1b[0;39;49m"
>   exitSuccess

"parsing"

> colorize :: (String, String) -> Maybe String
> colorize (fg, bg) = do
>   fore <- fgColorCode fg
>   back <- bgColorCode bg
>   return $ fore ++ back

Is this a terrible way to handle command line args, or the worst way to handle command line args?

> fgColorCode :: String -> Maybe String
> fgColorCode x = case (map toLower x) of
>   "null"         -> Just ""
>   "red"          -> Just "\x1b[31m"
>   "green"        -> Just "\x1b[32m"
>   "yellow"       -> Just "\x1b[33m"
>   "blue"         -> Just "\x1b[34m"
>   "magenta"      -> Just "\x1b[35m"
>   "cyan"         -> Just "\x1b[36m"
>   "white"        -> Just "\x1b[37m"
>   "lightred"     -> Just "\x1b[1;31m"
>   "lightgreen"   -> Just "\x1b[1;32m"
>   "lightyellow"  -> Just "\x1b[1;33m"
>   "lightblue"    -> Just "\x1b[1;34m"
>   "lightmagenta" -> Just "\x1b[1;35m"
>   "lightcyan"    -> Just "\x1b[1;36m"
>   "lightwhite"   -> Just "\x1b[1;37m"
>   _              -> Nothing
> 
> bgColorCode :: String -> Maybe String
> bgColorCode x = case (map toLower x) of
>   "null"         -> Just ""
>   "red"          -> Just "\x1b[41m"
>   "green"        -> Just "\x1b[42m"
>   "yellow"       -> Just "\x1b[43m"
>   "blue"         -> Just "\x1b[44m"
>   "magenta"      -> Just "\x1b[45m"
>   "cyan"         -> Just "\x1b[46m"
>   "white"        -> Just "\x1b[47m"
>   "lightred"     -> Just "\x1b[1;41m"
>   "lightgreen"   -> Just "\x1b[1;42m"
>   "lightyellow"  -> Just "\x1b[1;43m"
>   "lightblue"    -> Just "\x1b[1;44m"
>   "lightmagenta" -> Just "\x1b[1;45m"
>   "lightcyan"    -> Just "\x1b[1;46m"
>   "lightwhite"   -> Just "\x1b[1;47m"
>   _              -> Nothing

What passes for documentation.

> showUsage :: IO ()
> showUsage = do
>   putStr $ unlines
>     [ "doppler colors stdin with ANSI (A doppler-shifted echo)"
>     , "  USAGE: doppler FGCOLOR [BGCOLOR]"
>     , "    colors are red, green, yellow, blue,"
>     , "    magenta, cyan, white, and light colors."
>     , "  Examples:"
>     , "    echo \"wut\" | doppler red"
>     , "    echo \"hello\" | doppler lightgreen cyan"
>     ]