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|
{-----------------------------------------------------------------------------
reactive-banana
Example: "The world's worst synthesizer"
from the unofficial tutorial.
<http://wiki.haskell.org/FRP_explanation_using_reactive-banana>
------------------------------------------------------------------------------}
{-# LANGUAGE RecursiveDo #-}
-- allows recursive do notation
-- mdo
-- ...
module Main where
import Data.Char (toUpper)
import Control.Monad (forever)
import System.IO (BufferMode(..), hSetEcho, hSetBuffering, stdin)
import Reactive.Banana
import Reactive.Banana.Frameworks
type Octave = Int
data Pitch = PA | PB | PC | PD | PE | PF | PG
deriving (Eq, Enum)
-- Mapping between pitch and the char responsible for it.
pitchChars :: [(Pitch, Char)]
pitchChars = [(p, toEnum $ fromEnum 'a' + fromEnum p) |
p <- [PA .. PG]]
-- Reverse of pitchChars
charPitches :: [(Char, Pitch)]
charPitches = [(b, a) | (a, b) <- pitchChars]
data Note = Note Octave Pitch
instance Show Pitch where
show p = case lookup p pitchChars of
Nothing -> error "cannot happen"
Just c -> [toUpper c]
instance Show Note where
show (Note o p) = show p ++ show o
-- Filter and transform events at the same time.
filterMapJust :: (a -> Maybe b) -> Event a -> Event b
filterMapJust f = filterJust . fmap f
-- Change the original octave by adding a number of octaves, taking
-- care to limit the resulting octave to the 0..10 range.
changeOctave :: Int -> Octave -> Octave
changeOctave d = max 0 . min 10 . (d+)
-- Get the octave change for the '+' and '-' chars.
getOctaveChange :: Char -> Maybe Int
getOctaveChange c = case c of
'+' -> Just 1
'-' -> Just (-1)
_ -> Nothing
makeNetworkDescription :: AddHandler Char -> MomentIO ()
makeNetworkDescription addKeyEvent = do
eKey <- fromAddHandler addKeyEvent
let eOctaveChange = filterMapJust getOctaveChange eKey
bOctave <- accumB 3 (changeOctave <$> eOctaveChange)
let ePitch = filterMapJust (`lookup` charPitches) eKey
bPitch <- stepper PC ePitch
let
bNote = Note <$> bOctave <*> bPitch
foo = Note 0 PA
eNoteChanged <- changes bNote
reactimate' $ fmap (\n -> putStrLn ("Now playing " ++ show n))
<$> eNoteChanged
main :: IO ()
main = do
(addKeyEvent, fireKey) <- newAddHandler
network <- compile (makeNetworkDescription addKeyEvent)
actuate network
hSetEcho stdin False
hSetBuffering stdin NoBuffering
forever (getChar >>= fireKey)
|
