Slides in your GHCi

.ghci

import qualified System.IO.Strict as StrictIO
import qualified System.Directory as Dir
import qualified Data.Text as T

:set +m
:set prompt "\ESC[1;34m%s\n\ESC[0;34mλ> \ESC[m"

:set -XNoMonomorphismRestriction
:set -XRankNTypes
:set -XOverloadedStrings
:set -XScopedTypeVariables

-- Slides in my ghci!

let slide_ = StrictIO.readFile ".slide"

let xpp_ x = show $ (read x) + 1

let xmm_ x = show $ (read x) - 1

let slide_fioZero = do { writeFile ".slide" "0" ;
                 return "0" }

let slide_fioPlusPlus = do { x <- slide_ ;
                             writeFile ".slide" $ xpp_ x ;
                             return $ xpp_ x }

let slide_fioMinusMinus = do { x <- slide_ ;
                               writeFile ".slide" $ xmm_ x ;
                               return $ xmm_ x }

let slide_fioPut x = do { writeFile ".slide" x ;
                          return x }

let slide_present _ = return $ unlines [ "slide <- slide_fioZero"
                                 , ":!clear"
                                 ,  ":next" ]

let slide_next _ = let loadMaybe x = do {
                      que <- Dir.doesFileExist (x ++ ".hs") ;
                      if que
                        then return [ ":!clear"
                                    , "lastRead <- readFile \"" ++ x ++ ".hs\""
                                    , "putStrLn lastRead"
                                    , ":load " ++ x ++ ".hs" ]
                        else return []
                    } in do {
                    ioSlide <- slide_fioPlusPlus ;
                    ioCode  <- loadMaybe ioSlide ;
                    return $ unlines $ [ ":!clear"
                                       , "lastRead <- readFile \"" ++ ioSlide ++ ".txt\""
                                       , "putStr lastRead"
                                       , ":!read"
                                       ] ++ (ioCode :: [String]) ++ [ ":script ~/.ghci" ] }

let slide_previous _ = slide_fioMinusMinus >> slide_fioMinusMinus >> slide_next ""

let slide_goto x = slide_fioPut x >> slide_fioMinusMinus >> slide_next ""

:def! present slide_present
:def! next slide_next
:def! previous slide_previous
:def! goto slide_goto