feat: pretty-print expressions

1 files changed, 11 insertions, 1 deletions

diff --git a/lambda-calcul/haskell/src/Minilang/Lambda/Parser.hs b/lambda-calcul/haskell/src/Minilang/Lambda/Parser.hs
index f18ac74..28da47f 100644
--- a/lambda-calcul/haskell/src/Minilang/Lambda/Parser.hs
+++ b/lambda-calcul/haskell/src/Minilang/Lambda/Parser.hs
@@ -1,8 +1,12 @@
+{-# LANGUAGE LambdaCase #-}
+
 module Minilang.Lambda.Parser where
 
 import Control.Applicative (Alternative (many), (<|>))
 import Data.Bifunctor (first)
-import Data.Text (Text, pack)
+import qualified Data.List as List
+import Data.Text (Text, intersperse, pack)
+import qualified Data.Text as Text
 import Data.Void (Void)
 import Text.Megaparsec (Parsec, between, empty, errorBundlePretty, manyTill, notFollowedBy, optional, parse, try)
 import Text.Megaparsec.Char (alphaNumChar, char, letterChar, space1, string, symbolChar)
@@ -16,6 +20,12 @@ data ParseError = ParseError Text
 data AST = Sym Text | Abs [Text] AST | App AST AST [AST]
   deriving (Eq, Show)
 
+pretty :: AST -> Text
+pretty = \case
+  Sym sym -> sym
+  Abs bound body -> "(lam (" <> Text.unwords bound <> ") " <> pretty body <> ")"
+  App x y rest -> "(" <> mconcat (List.intersperse " " (pretty <$> (x : y : rest))) <> ")"
+
 parse :: Text -> Either ParseError AST
 parse =
   first (ParseError . pack . errorBundlePretty) . Text.Megaparsec.parse ast ""