Miscellaneous

1 Miscellaneous

1.1 Haskell IDEs and Text Editors

1.2 GHCI configuration file

The ghci configuration file allows the user to create custom commands and customize the ghci shell. The file is in the directory ~/.ghci in Unix systems like Linux and OSX.

Example: ~/.ghci

import System.Directory ( getCurrentDirectory)
import System.Process (readProcess)

:set -hide-package mtl

:set prompt "\x1b[32m>\x1b[0m " -- set the shell prompt to print λ (lambda)

:def hoogle \s -> return $ ":! hoogle --count=15 \"" ++ s ++ "\""

let xclip_ =  readProcess "xclip" ["-o", "-selection", "clipboard"] ""

let __savePasted = do {  code <-  readProcess "xclip" ["-o", "-selection", "clipboard"] ""  ;  putStrLn 

code ; writeFile "/tmp/haskTemp.hs" code}

let pwd = getCurrentDirectory >>= putStrLn

:def paste (\_ -> __savePasted >> return ":load /tmp/haskTemp.hs" )
:def pwd (\_ -> pwd >> return "")

It requires hoogle to be installed on Linux: (sudo apt-get install hoogle) on Ubuntu.

Examples:

:paste - Paste code block in clipboard and compiles it in ghci
:pwd   - Show Current Directory

> :pwd
/home/tux/PycharmProjects/Haskell
> 
> 

> :hoogle getCurrentDirectory
Directory getCurrentDirectory :: IO FilePath
System.Directory getCurrentDirectory :: IO FilePath
> 


> :paste
import Data.Time.Clock
import Data.Time.Calendar
import Data.Time.LocalTime

main = do
    now <- getCurrentTime
    timezone <- getCurrentTimeZone
    let zoneNow = utcToLocalTime timezone now
    let (year, month, day) = toGregorian $ localDay zoneNow
    putStrLn $ "Year: " ++ show year
    putStrLn $ "Month: " ++ show month
    putStrLn $ "Day: " ++ show day
[1 of 1] Compiling Main             ( /tmp/haskTemp.hs, interpreted )
Ok, modules loaded: Main.
> 
> main
Year: 2015
Month: 4
Day: 26
>

1.3 Troubleshooting

1.3.1 Importing Ambigous Modules in GHCi

> import Control.Monad.State

<no location info>:
    Ambiguous module name `Control.Monad.State':
      it was found in multiple packages: monads-tf-0.1.0.2 mtl-2.2.1
> 

> :set -hide-package mtl
> import Control.Monad.State
>

Solution: Add the line to ~/.ghci

:set -hide-package mtl