Execute Brain****/Haskell: Difference between revisions
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Fixed syntax highlighting.
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{{implementation|Brainf***}}{{collection|RCBF}}
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).
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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
moveLeft (x:l,r) = (l,x:r)▼
moveRight (l,x:r) = (x:l,r) ▼
matchLeft d@(']':_,_) = matchLeft $ moveLeft $ matchLeft $ moveLeft $ d▼
matchLeft d = matchLeft $ moveLeft $ d
matchRight d@(_,']':_) = moveRight $ d▼
matchRight d@(_,'[':_) = matchRight $ matchRight $ moveRight $ d▼
pad ([],[]) = ([0],[0])▼
pad ([],r) = ([0],r)▼
pad d = d
modify f (l,x:r) = (l,(f x):r)▼
exec :: (String, String) -> ([Integer], [Integer]) -> [Integer] -> [Integer]▼
exec p@(_,'>':_) d cs = exec (moveRight p) (pad $ moveRight $ d) cs▼
exec p@(_,']':_) d cs = exec (matchLeft $ moveLeft $ p) d cs
run :: String -> [Integer] -> [Integer]▼
dialog :: String -> IO ()▼
dialog s = mapM_ print . run s . map read . 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>
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