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Revision as of 00:12, 15 April 2008 (view source) rosettacode>Spoon! mNo edit summary ← Older edit		Latest revision as of 11:24, 1 September 2022 (view source) PureFox (talk \| contribs) m (Fixed syntax highlighting.)
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Line 1: {{implementation\|Brainf**}}{{collection\|RCBF}}~~[[Category:Haskell]]~~ Quick implementation of a [[Brainfuck]] interpreter in [[Haskell]]. Pairs of lists are used to implement both the two-side infinite band of cells, and the program storage. This means that it can also work on infinite Brainfuck programs (which could be generated lazily). In functional style, ''run'' interprets a Brainfuck program as a function from an Integer list (inputs) to an Integer list (outputs). ~~With help of ''unsafePerformIO'', this~~This can be easily turned into a real dialog with a user via ''stdin'' and ''stdout''. A more efficient implementation could for example only admit well-bracketed brainfuck programs, and parse bracket blocks first, to replace the ''matchLeft'' and ''matchRight'' which need linear time. <syntaxhighlight lang="haskell">module BF where ~~import System.IO.Unsafe~~ moveLeft (x:l,r) = (l,x:r) moveRight (l,x:r) = (x:l,r) matchLeft d@('[':_,_) = d matchLeft d@(']':_,_) = matchLeft $ moveLeft $ matchLeft $ moveLeft $ d matchLeft d = matchLeft $ moveLeft $ d matchRight d@(_,']':_) = moveRight $ d matchRight d@(_,'[':_) = matchRight $ matchRight $ moveRight $ d matchRight d = matchRight $ moveRight $ d pad ([],[]) = ([0],[0]) pad ([],r) = ([0],r) pad (l,[]) = (l,[0]) pad d = d modify f (l,x:r) = (l,(f x):r) exec :: (String, String) -> ([Integer], [Integer]) -> [Integer] -> [Integer] exec (_,[]) _ _ = [] exec p@(_,'>':_) d cs = exec (moveRight p) (pad $ moveRight $ d) cs exec p@(_,'<':_) d cs = exec (moveRight p) (pad $ moveLeft $ d) cs exec p@(_,'+':_) d cs = exec (moveRight p) (modify (+ 1) d) cs exec p@(_,'-':_) d cs = exec (moveRight p) (modify (-subtract 1) d) cs exec p@(_,',':_) d (c:cs) = exec (moveRight p) (modify (const c) d) cs exec p@(_,'.':_) d@(_,x:_) cs = x : exec (moveRight p) d cs exec p@(_,'[':_) d@(_,0:_) cs = exec (matchRight $ moveRight $ p) d cs exec p@(_,'[':_) d cs = exec (moveRight p) d cs exec p@(_,']':_) d@(_,0:_) cs = exec (moveRight p) d cs exec p@(_,']':_) d cs = exec (matchLeft $ moveLeft $ p) d cs run :: String -> [Integer] -> [Integer] run s = exec ([],s) ([0],[0]) dialog :: String -> IO () dialog s = mapM_ print $. run s $. ~~repeat~~map ~~(unsafePerformIO~~read ~~readLn)~~. lines =<< getContents </syntaxhighlight>(This version compiles with GHC and will run if loaded into ghci using ':load BF') Example session: <pre> : Main> dialog ",[>+<-].>." : ''5'' : 0 : 5 </pre>