代写代考 module RoverModel where

module RoverModel where

import Data.Word
import RoverInterface

Copyright By PowCoder代写 加微信 powcoder

This is a very simple implementation of `MonadFloppy`,
mostly useful for testing. Each track is represented
as a list of bytes `[Word8]`. The state of the disk
consists of the track under the head (`[Word8]`) and
two lists `[[Word8]]` representing the tracks behind
and in front of the head.

This simple model does not simulate disk spinning: all
reads and writes start from the same predictable
location. However, it’s still useful for testing and
debugging your monadic code.

You are encouraged to develop your own, more sophisticated
disk model using this one as a template.

data DiskState =
DiskState [[Word8]] [Word8] [[Word8]]

— `DiskModel` is very similar to `State DiskState`.
data DiskModel a = DiskModel (DiskState -> (a, DiskState))

— An empty disk state.
emptyDisk :: DiskState
emptyDisk =
DiskState [] (replicate 2048 0) (map (\x -> replicate 2048 0) [1..39])

runDiskModel :: DiskModel a -> DiskState -> (a, DiskState)
runDiskModel (DiskModel f) = f

execDiskModel :: DiskModel a -> DiskState -> DiskState
execDiskModel s = snd . runDiskModel s

evalDiskModel :: DiskModel a -> DiskState -> a
evalDiskModel s = fst . runDiskModel s

— Implemented just like the State monad.
instance Monad DiskModel where
return x = DiskModel (\s -> (x,s))
DiskModel f >>= g = DiskModel (\s ->
let (x,s’) = f s in runDiskModel (g x) s’)
instance Applicative DiskModel where
pure = return
f <*> x = do
return (f’ x’)
instance Functor DiskModel where
fmap f x = do
return (f x’)

— `DiskModel` implements the four `MonadFloppy`
— operations in a naive way.
instance MonadFloppy DiskModel where
headForward = DiskModel $ \(DiskState pre c post) ->
case post of
[] -> ((), DiskState pre c post)
(p:post) -> ((), DiskState (c:pre) p post)
headBackward = DiskModel $ \(DiskState pre c post) ->
case pre of
[] -> ((), DiskState pre c post)
(p:pre) -> ((), DiskState pre p (c:post))
readTrack = DiskModel $ \(DiskState pre c post) ->
(take 2048 (c ++ repeat 0), DiskState pre c post)
writeTrack t = DiskModel $ \(DiskState pre c post) ->
((), DiskState pre (take 2048 $ t ++ drop (length t) c) post)

— This show function lets us print the first few bytes of
— the non-zero tracks. Very useful for debugging.
instance Show DiskState where
show (DiskState pre c post) = “DiskState: \n” ++ concat
[” ” ++ show n ++ ” ” ++ p ++ “\n” | (n,p) <- zip [0..] peek] where tracks = reverse pre ++ [c] ++ post nztracks = filter (/= replicate 2048 0) tracks peek = map ((++"..") . show . take 10) nztracks 程序代写 CS代考 加微信: powcoder QQ: 1823890830 Email: powcoder@163.com