tttardigrado · November 24, 2024 08:42 · Nov 23, 2024 · Nov 23, 2024
diff --git a/pll.hs b/pll.hs
@@ -11,7 +11,7 @@ left (Tape (l:ls) v rs) = Tape ls l (v:rs)
 right :: Tape -> Tape
 right (Tape ls v (r:rs)) = Tape (v:ls) r rs
 
-peek :: Tape -> Tape
+peek :: Tape -> Int
 peek (Tape _ v _) = v
 
 edit :: (Int -> Int) -> Tape -> Tape

diff --git a/pll.hs b/pll.hs
@@ -0,0 +1,29 @@
+data P = R | L | Seq P P | Loop P
+
+data Tape = Tape [Int] Int [Int]
+
+empty :: Tape
+empty = Tape (repeat 0) 0 (repeat 0)
+
+left :: Tape -> Tape
+left (Tape (l:ls) v rs) = Tape ls l (v:rs)
+
+right :: Tape -> Tape
+right (Tape ls v (r:rs)) = Tape (v:ls) r rs
+
+peek :: Tape -> Tape
+peek (Tape _ v _) = v
+
+edit :: (Int -> Int) -> Tape -> Tape
+edit f (Tape ls v rs) = Tape ls (f v) rs
+
+run :: Int -> P -> Tape -> Tape
+run n R t = right t
+run n L t = left $ edit ((`mod`n) . (+1)) t
+run n (Seq p q) t = run n q $ run n p t
+run n (Loop  p) t = if peek t == 0
+  then t
+  else run n (Seq p $ Loop p) t
+
+eval :: P -> Int
+eval p = peek $ run 256 p empty