pretty printing

app/Expr.hs

@@ -3,15 +3,39 @@
 module Expr where
 
 import Data.Function (on)
+import Data.List (genericDrop)
 
 data Expr where
-  Var :: Integer -> Expr
-  Star :: Expr
-  Square :: Expr
-  App :: Expr -> Expr -> Expr
-  Abs :: Expr -> Expr -> Expr
-  Pi :: Expr -> Expr -> Expr
-  deriving (Show, Eq)
+    Var :: Integer -> Expr
+    Star :: Expr
+    Square :: Expr
+    App :: Expr -> Expr -> Expr
+    Abs :: Expr -> Expr -> Expr
+    Pi :: Expr -> Expr -> Expr
+    deriving (Show, Eq)
+
+{- --------------------- PRETTY PRINTING ----------------------------- -}
+
+-- TODO : store parsed identifiers for better printing
+genName :: Integer -> String
+genName k = case genericDrop k ["x", "y", "z", "w", "u", "v"] of
+    [] -> 'x' : show (k - 6)
+    (v : _) -> v
+
+pretty :: Expr -> String
+pretty = helper 0
+  where
+    helper :: Integer -> Expr -> String
+    helper k (Var n) = genName $ k - n - 1
+    helper _ Star = "*"
+    helper _ Square = "□"
+    helper k (App e1 e2) = "(" ++ helper k e1 ++ " " ++ helper k e2 ++ ")"
+    helper k (Abs ty b) =
+        "(λ" ++ genName k ++ " : " ++ helper k ty ++ " . " ++ helper (k + 1) b ++ ")"
+    helper k (Pi ty b) =
+        "(∏" ++ genName k ++ " : " ++ helper k ty ++ " . " ++ helper (k + 1) b ++ ")"
+
+{- --------------- ACTUAL MATH STUFF ---------------- -}
 
 isSort :: Expr -> Bool
 isSort Star = True

app/Main.hs

@@ -1,13 +1,14 @@
 module Main where
 
+import Expr
 import Parser
 import System.IO
 
 main :: IO ()
 main = do
-  _ <- putStr "> "
-  _ <- hFlush stdout
-  input <- getLine
-  case pAll input of
-    Left err -> putStrLn err
-    Right expr -> print expr
+    _ <- putStr "> "
+    _ <- hFlush stdout
+    input <- getLine
+    case pAll input of
+        Left err -> putStrLn err
+        Right expr -> putStrLn $ pretty expr