Execute SNUSP/Haskell: Difference between revisions

The Haskell code starts with lots of imports:

 

import System.IO

import System.Random

import Data.Array

 

 

Use a list as an index into an array:

 

 

instance Ix a => Ix [a] where

inRange ([],[]) [] = True

inRange (l:ls, u:us) (i:is) = inRange (l,u) i && inRange (ls,us) is

 

or into an hashtable (the hash function could probably be improved):

 

cmpList [] [] = True

cmpList (x:xs) [] = x == 0 && cmpList xs []

combine :: Int -> Int -> Int

combine x 0 = x

 

Here it's important that index lists with trailing zeroes are treated just like this list without the zeroes, so we can handle any number of dimensions. We want the same flexibility when adding index lists:

 

[] <+> ys = ys

xs <+> [] = xs

 

Some helper functions:

 

 

modify d t f = do

 

toChar = chr . fromInteger

 

Now, the commands. Given a thread, return a list of threads valid after one simulation step. In that way, ''exec'' can handle forks and thread termination on errors.

 

 

exec '+' d t = modify d t (+1)

-- NOOP

 

 

The scheduler manages a list ''ts'' of active threads, and a list ''ks'' of threads waiting for input. If there are no more threads in either list, stop. If input is available, one blocked thread is executed. If no input is available and all threads are blocked, we block the interpreter, too (so the OS can do something else). Otherwise, try to execute one of the unblocked threads, first checking if it's still inside the code array.

 

 

run c d = schedule [thread] [] False where

| x == ',' = return ([],[t])

| otherwise = exec' x d t

 

Finally, routines to run code from a string or a file, and the main program.

 

d <- H.new cmpList hashList

let x = length s `div` y

hSetBuffering stdin NoBuffering

[s] <- getArgs

 

 

To demonstrate the ease of introducing even more dimensions, let's implement commands ( and ) to move the data pointer along the z-axis, and a command ^ to rotate the IP direction around the (1,1,1) axis (i.e., left becomes up, up becomes "farther" on the z-axis, "farther" becomes left, etc.).

 

exec ')' d t = moveMp d t [0,0, 1]