Execute SNUSP/Haskell: Difference between revisions

The Haskell code starts with lots of imports:

import System.Environment

import System.IO

import qualified Data.HashTable as H

Use a list as an index into an array:

type Index = [Int]

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

rangeSize (ls,us) = product $ map rangeSize $ zip ls us

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

cmpList :: Index -> Index -> Bool

cmpList [] [] = True

combine x 0 = x

combine x y = z * (z+1) `div` 2 + x where z = x + y

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:

(<+>) :: Index -> Index -> Index

[] <+> ys = ys

xs <+> [] = xs

(x:xs) <+> (y:ys) = (x+y) : (xs <+> ys)

Some helper functions:

data Thread a = T {mp::a, ip::a, dir::a, stack::[(a,a)]} deriving Show

toChar = chr . fromInteger

fromChar = toInteger . ord

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.

-- Core SNUSP

exec _ d t = return [t]

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.

start c = maybe (fst $ bounds $ c) fst $ find (\(_,x) -> x == '$') $ assocs c

| otherwise = exec' x d t

where x = c ! (ip t)

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

runString y s = do

d <- H.new cmpList hashList

[s] <- getArgs

runFile s

== Extension ==

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]

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

exec '^' d t = return [t {dir=(d3:d1:d2:ds)}] where d1:d2:d3:ds = dir t <+> [0,0,0]