From c3a175e808b279eb415bcb5dbcb9db5f34035f98 Mon Sep 17 00:00:00 2001
From: Arnaud Bailly <arnaud@pankzsoft.com>
Date: Fri, 17 Oct 2025 09:52:06 +0200
Subject: feat: add basic application to evaluate "programs"

The main simply reads from its stdin, evaluates its input, and dump
the result of the evaluation.
---
 lambda-calcul/haskell/app/Main.hs                 |  6 ++++
 lambda-calcul/haskell/minilang.cabal              | 25 +++++++++++++++
 lambda-calcul/haskell/src/Minilang/IO.hs          | 32 +++++---------------
 lambda-calcul/haskell/src/Minilang/Lambda/Eval.hs |  2 +-
 lambda-calcul/haskell/test/Minilang/IOSpec.hs     | 37 +++++++++++++++++++++++
 5 files changed, 77 insertions(+), 25 deletions(-)
 create mode 100644 lambda-calcul/haskell/app/Main.hs
 create mode 100644 lambda-calcul/haskell/test/Minilang/IOSpec.hs

diff --git a/lambda-calcul/haskell/app/Main.hs b/lambda-calcul/haskell/app/Main.hs
new file mode 100644
index 0000000..5b48c01
--- /dev/null
+++ b/lambda-calcul/haskell/app/Main.hs
@@ -0,0 +1,6 @@
+import Minilang.IO
+import System.IO (stdin, stdout)
+
+main :: IO ()
+main =
+  runEval stdin stdout
diff --git a/lambda-calcul/haskell/minilang.cabal b/lambda-calcul/haskell/minilang.cabal
index 817672e..7c9c266 100644
--- a/lambda-calcul/haskell/minilang.cabal
+++ b/lambda-calcul/haskell/minilang.cabal
@@ -25,6 +25,7 @@ source-repository head
 
 library
   exposed-modules:
+      Minilang.IO
       Minilang.Lambda.Unify
       Minilang.Lambda.Eval
       Minilang.Lambda.Infer
@@ -60,6 +61,7 @@ test-suite minilang-test
   type: exitcode-stdio-1.0
   main-is: Spec.hs
   other-modules:
+      Minilang.IOSpec
       Minilang.Lambda.InferSpec
       Minilang.Lambda.EvalSpec
   hs-source-dirs:
@@ -91,5 +93,28 @@ test-suite minilang-test
     , minilang
     , mtl
     , text
+    , unix
     , unordered-containers
   default-language: Haskell2010
+
+executable lambda
+  main-is: Main.hs
+  other-modules:
+      Paths_minilang
+  hs-source-dirs:
+      app
+  default-extensions:
+      DeriveGeneric
+      OverloadedStrings
+      FlexibleInstances
+      MultiParamTypeClasses
+      FlexibleContexts
+      RecordWildCards
+      NamedFieldPuns
+      GeneralizedNewtypeDeriving
+  ghc-options: -Wall -fno-warn-orphans -threaded -rtsopts -with-rtsopts=-N
+  build-depends:
+      base
+    , containers
+    , minilang
+  default-language: Haskell2010
diff --git a/lambda-calcul/haskell/src/Minilang/IO.hs b/lambda-calcul/haskell/src/Minilang/IO.hs
index bfcb125..c468316 100644
--- a/lambda-calcul/haskell/src/Minilang/IO.hs
+++ b/lambda-calcul/haskell/src/Minilang/IO.hs
@@ -1,40 +1,24 @@
-{-# LANGUAGE DuplicateRecordFields #-}
-{-# LANGUAGE GeneralizedNewtypeDeriving #-}
-{-# LANGUAGE NamedFieldPuns #-}
-{-# LANGUAGE RecordWildCards #-}
-{-# LANGUAGE TypeSynonymInstances #-}
-{-# OPTIONS_GHC "-fno-warn-orphans" #-}
-
 module Minilang.IO where
 
 import qualified Data.ByteString as BS
+import qualified Data.Text as Text
 import Data.Text.Encoding
   ( decodeUtf8With,
     encodeUtf8,
   )
 import Data.Text.Encoding.Error (lenientDecode)
-import Minilang.Lambda.Eval hiding (rho)
-import Minilang.Parser
-import Minilang.Type
-import Prettyprinter
-import Prettyprinter.Render.Text
+import Minilang.Lambda.Eval (eval)
 import System.IO (Handle)
 
--- | Read an `AST` from @hin@ handle, evaluate it and dump the result
+-- | Read a "program" from @hin@ handle, evaluate it and dump the result
 -- on @hout@.
 runEval :: Handle -> Handle -> IO ()
 runEval hin hout = do
-  programText <- decodeUtf8With lenientDecode <$> BS.hGetContents hin
-  let ast = parseProgram False programText
-      ρ = EmptyEnv
-      γ = EmptyContext
-  (ρ', _) <- loadProgram ast ρ γ
-  let val = eval ast ρ'
+  programText <- Text.unpack . decodeUtf8With lenientDecode <$> BS.hGetContents hin
+  let ast = read programText
+      env = mempty
+      result = eval ast env
 
   BS.hPut
     hout
-    ( encodeUtf8
-        ( renderStrict $ layoutPretty defaultLayoutOptions $ pretty val
-        )
-        <> "\n"
-    )
+    (encodeUtf8 (Text.pack (show result) <> "\n"))
diff --git a/lambda-calcul/haskell/src/Minilang/Lambda/Eval.hs b/lambda-calcul/haskell/src/Minilang/Lambda/Eval.hs
index 68b01be..0829186 100644
--- a/lambda-calcul/haskell/src/Minilang/Lambda/Eval.hs
+++ b/lambda-calcul/haskell/src/Minilang/Lambda/Eval.hs
@@ -6,7 +6,7 @@ data Term
   = Var Text
   | Lam Text Term
   | App Term Term
-  deriving (Show, Eq)
+  deriving (Show, Read, Eq)
 
 type Env = [(Text, Term)]
 
diff --git a/lambda-calcul/haskell/test/Minilang/IOSpec.hs b/lambda-calcul/haskell/test/Minilang/IOSpec.hs
new file mode 100644
index 0000000..038877d
--- /dev/null
+++ b/lambda-calcul/haskell/test/Minilang/IOSpec.hs
@@ -0,0 +1,37 @@
+module Minilang.IOSpec where
+
+import Control.Exception (bracket)
+import Minilang.IO (runEval)
+import System.Directory (getTemporaryDirectory, removeFile)
+import System.FilePath ((<.>), (</>))
+import System.IO (IOMode (..), hClose, readFile, withFile, writeFile)
+import System.Posix (mkstemp)
+import Test.Hspec (Spec, around, describe, it, parallel, shouldBe)
+import Prelude hiding (lines, readFile, writeFile)
+
+spec :: Spec
+spec = parallel $
+  describe "MiniLang I/O Evaluator" $ do
+    around withTempFile $
+      it "evaluates a simple MiniLang 'program' and dumps result" $ \fileName -> do
+        let outputFileName = fileName <> ".out"
+            program =
+              [ "(App (Lam \"x\" (Var \"x\")) (Var \"y\"))"
+              ]
+
+        writeFile fileName (unlines program)
+
+        _ <- withFile fileName ReadMode $ \hin ->
+          withFile outputFileName AppendMode $ \hout ->
+            runEval hin hout
+
+        out <- readFile outputFileName
+
+        out `shouldBe` "Var \"y\"\n"
+
+withTempFile :: (String -> IO ()) -> IO ()
+withTempFile =
+  bracket mkTempFile rmTempFile
+  where
+    mkTempFile = getTemporaryDirectory >>= \dir -> mkstemp (dir </> "test-repl") >>= \(fp, h) -> hClose h >> pure fp
+    rmTempFile fn = removeFile fn >> removeFile (fn <.> "out")
-- 
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