Add builtin arithmetic operators

* also allow choosing evaluator
* ensures equivalence of evaluators up-to α-renaming
* checks server accepts answers from challenge

1 files changed, 30 insertions, 7 deletions

diff --git a/lambda-calcul/haskell/app/Main.hs b/lambda-calcul/haskell/app/Main.hs
index 6ba9321..8846c81 100644
--- a/lambda-calcul/haskell/app/Main.hs
+++ b/lambda-calcul/haskell/app/Main.hs
@@ -1,9 +1,11 @@
-import Minilang.REPL (withIO, withTerminal)
+import Minilang.REPL (evaluatorFromEnv, withIO, withTerminal)
+import Minilang.REPL.Types (Evaluator (..))
 import Minilang.Server (startServer, waitServer)
 import Options.Applicative
 import System.IO (stdin, stdout)
 import System.Posix.IO (stdInput)
 import System.Posix.Terminal (queryTerminal)
+import Text.Read (readMaybe)
 
 data RunMode
   = Local
@@ -12,7 +14,9 @@ data RunMode
 
 data Options = Options
   { serverPort :: Int,
-    runMode :: RunMode
+    runMode    :: RunMode,
+    -- | 'Nothing' means "read from MINILANG_EVAL env var".
+    evalOpt    :: Maybe Evaluator
   }
   deriving (Eq, Show)
 
@@ -26,7 +30,7 @@ optionsParser =
 
 minilangOptions :: Parser Options
 minilangOptions =
-  Options <$> portOption <*> runModeOption
+  Options <$> portOption <*> runModeOption <*> evalOption
 
 portOption :: Parser Int
 portOption =
@@ -36,7 +40,7 @@ portOption =
         <> short 'p'
         <> value 7890
         <> metavar "INT"
-        <> help "port to listent on (default: 7890)"
+        <> help "port to listen on (default: 7890)"
     )
 
 runModeOption :: Parser RunMode
@@ -49,13 +53,32 @@ runModeOption =
         <> help "run in server mode, listening for client REPLs over HTTP"
     )
 
+evalOption :: Parser (Maybe Evaluator)
+evalOption =
+  optional $
+    option
+      (eitherReader parseEvaluator)
+      ( long "eval"
+          <> short 'E'
+          <> metavar "EVALUATOR"
+          <> help "reduction strategy: DeBruijn (default) or NbE. \
+                  \Falls back to the MINILANG_EVAL environment variable."
+      )
+
+parseEvaluator :: String -> Either String Evaluator
+parseEvaluator s = case readMaybe s of
+  Just ev -> Right ev
+  Nothing -> Left $ "Unknown evaluator: " <> show s <> ". Valid values: DeBruijn, NbE"
+
 main :: IO ()
 main = do
   Options {..} <- execParser optionsParser
+  -- CLI flag takes precedence; fall back to env var.
+  ev <- maybe evaluatorFromEnv pure evalOpt
   case runMode of
     Local -> do
       hasTty <- queryTerminal stdInput
       if hasTty
-        then withTerminal
-        else withIO stdin stdout
-    Server -> startServer serverPort >>= waitServer
+        then withTerminal ev
+        else withIO ev stdin stdout
+    Server -> startServer serverPort ev >>= waitServer