Initial commit

lambda.hs

@@ -0,0 +1,69 @@
+import Data.List
+
+data StrSymbol = StrSymbol { symBase :: String -- lowercase a to z
+                           , symLen :: Int
+                           }
+
+instance Show StrSymbol where
+  show (StrSymbol s n) = s ++ (replicate n '\'')
+
+class Symbol a where
+  -- Should we use a set instead of a list here? ~G
+  --   Hardly five minutes away and you're already overengineering. ~X
+  --   Overengineering is fun! ~G
+  -- Also, what is the second parameter? ~X
+  --   The original symbol for which a new name should be found ~G (grammer is herd)
+  --     Do we need that or can we just let it return a new symbol? ~X
+  --     If we just let it return a new symbol, we would lose the thing where something called a will be renamed to a'
+  --     and later back to a (keep the same name) ~G
+  --     How about we define a findNewName that just finds a new unique symbol that is not in the list, so we can try out both
+  --     things later on. ~G
+  findName :: [a] -> a -> a
+  findNewName :: [a] -> a
+
+instance Symbol StrSymbol where
+  findName other (StrSymbol base n) =
+    let sameBase = filter ((base ==) . symBase) other
+        lengths = map symLen sameBase
+        freeLengths = [0..] \\ (nub lengths)
+    in  StrSymbol base (head freeLengths) -- [0..] is infinite
+  
+  -- findNewName basically finds a new unique base ~G
+  -- try to find a name in the sequence
+  -- a..z, aa..zz, aaa........
+  {-
+  findNewName other =
+    let bases = nub $ map symBase other
+  -}
+
+data Expression s = ESymbol s
+                  | EExpr   (Expression s) (Expression s)
+                  | ELambda s (Expression s)
+
+instance (Show s) => Show (Expression s) where
+  show (ESymbol s) = show s
+  -- show (EExpr a e@(EExpr _ _)) = "(" ++ show a ++ " " ++ (drop 1 $ show e) -- hack hack hack
+  show (EExpr a@(EExpr _ _) b) = (init $ show a) ++ " " ++ show b ++ ")" -- hack hack hack
+  show (EExpr a b) = "(" ++ show a ++ " " ++ show b ++ ")"
+  show (ELambda s e) = "\\" ++ show s ++ "." ++ show e
+
+_s :: String -> Expression StrSymbol
+_s s = ESymbol (StrSymbol s 0)
+
+_ss :: String -> StrSymbol
+_ss s = (StrSymbol s 0)
+
+main = do
+  print (EExpr (_s "a") (EExpr (_s "b") (_s "c")))
+  print (EExpr (_s "a") (EExpr (_s "b") (EExpr (_s "c") (_s "d"))))
+  print (EExpr (EExpr (_s "a") (_s "b")) (_s "c"))
+  print (EExpr (EExpr (EExpr (_s "a") (_s "b")) (_s "c")) (_s "d"))
+  print (EExpr (EExpr (_s "a") (EExpr (_s "b") (_s "c"))) (_s "d"))
+  print (ELambda (StrSymbol "a" 0) (_s "a"))
+  print (ELambda (StrSymbol "a" 0) (EExpr (EExpr (_s "a") (EExpr (_s "b") (_s "c"))) (_s "d")))
+  
+  -- test of findName (seems to be working) ~G
+  print $ findName [(StrSymbol "a" 0), (StrSymbol "b" 0), (StrSymbol "a" 1)] (StrSymbol "a" 4)
+  print $ findName [(StrSymbol "a" 0), (StrSymbol "b" 0), (StrSymbol "a" 1)] (StrSymbol "b" 3)
+  print $ findName [(StrSymbol "a" 0), (StrSymbol "b" 0), (StrSymbol "a" 1)] (StrSymbol "c" 2)
+  print $ findName [(StrSymbol "a" 1), (StrSymbol "a" 3), (StrSymbol "a" 0)] (StrSymbol "a" 1)