From a210419fd60c00d011f70fb1b968031621e4c01a Mon Sep 17 00:00:00 2001
From: Arnaud Bailly <arnaud@pankzsoft.com>
Date: Tue, 28 Oct 2025 18:34:16 +0100
Subject: Provide function to go back from a deBruijn term to an AST

---
 lambda-calcul/haskell/src/Minilang/IO.hs | 28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

(limited to 'lambda-calcul/haskell/src/Minilang/IO.hs')

diff --git a/lambda-calcul/haskell/src/Minilang/IO.hs b/lambda-calcul/haskell/src/Minilang/IO.hs
index a045647..b2b3dcc 100644
--- a/lambda-calcul/haskell/src/Minilang/IO.hs
+++ b/lambda-calcul/haskell/src/Minilang/IO.hs
@@ -7,8 +7,8 @@ import Data.Text.Encoding
     encodeUtf8,
   )
 import Data.Text.Encoding.Error (lenientDecode)
-import Minilang.Lambda.DeBruijn (eval, toDeBruijn)
-import Minilang.Lambda.Parser (desugar, parse, pretty)
+import Minilang.Lambda.DeBruijn (eval, fromDeBruijn, toDeBruijn)
+import Minilang.Lambda.Parser (desugar, parse, pretty, resugar)
 import System.IO (Handle)
 
 -- | Read a "program" from @hin@ handle, evaluate it and dump the result
@@ -17,11 +17,19 @@ runEval :: Handle -> Handle -> IO ()
 runEval hin hout = do
   programText <- decodeUtf8With lenientDecode <$> BS.hGetContents hin
   let parsed = parse programText
-  case parsed of
-    Left err -> print err
-    Right ast -> do
-      putStrLn $ Text.unpack $ "Evaluating " <> pretty ast
-      let termy = desugar ast
-      putStrLn $ "Desugared to " <> show termy
-      let term = toDeBruijn termy
-      print $ eval term
+  let result =
+        case parsed of
+          Left err -> Text.pack $ show err
+          Right ast ->
+            let evaluate =
+                  pretty
+                    . resugar
+                    . fromDeBruijn
+                    . eval
+                    . toDeBruijn
+                    . desugar
+             in evaluate ast
+
+  BS.hPut
+    hout
+    (encodeUtf8 result)
-- 
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