2 files changed, 111 insertions, 0 deletions
diff --git a/src/Eval.hs b/src/Eval.hs
new file mode 100644
index 0000000..72c8985
--- /dev/null
+++ b/src/Eval.hs
@@ -0,0 +1,45 @@
+module Eval
+  ( evalMain
+  ) where
+
+import           Control.Exception
+import           Control.Monad.State
+import           System.Console.Haskeline
+import           System.Environment
+import           System.Exit
+import           System.IO
+
+type Environment = [String]
+
+eval :: String -> IO ()
+eval code = putStrLn "ok"
+
+evalFile :: String -> IO ()
+evalFile path = do
+  file <- try $ readFile path :: IO (Either IOError String)
+  case file of
+    Left  exception -> print (exception :: IOError)
+    Right file      -> eval file
+
+evalRepl :: String -> Environment -> InputT IO Environment
+evalRepl line env = outputStrLn (show env) >> pure env
+
+repl :: Environment -> InputT IO ()
+repl env =
+  getInputLine ":: "
+    >>= (\case
+          Nothing   -> pure ()
+          Just line -> evalRepl line env >>= repl
+        )
+
+usage :: IO ()
+usage = putStrLn "Invalid arguments. Use 'bruijn [file]' instead"
+
+evalMain :: IO ()
+evalMain = do
+  args <- getArgs
+  case args of
+    [] -> runInputT defaultSettings { historyFile = Just ".brown-history" }
+      $ repl []
+    [path] -> evalFile path
+    _      -> usage
diff --git a/src/Parser.hs b/src/Parser.hs
new file mode 100644
index 0000000..611261f
--- /dev/null
+++ b/src/Parser.hs
@@ -0,0 +1,66 @@
+module Parser where
+
+import           Data.Functor.Identity
+import           Text.Parsec
+import           Text.Parsec.Language
+import qualified Text.Parsec.Token             as Token
+
+languageDef :: GenLanguageDef String u Identity
+languageDef = emptyDef { Token.commentLine     = "#"
+                       , Token.identStart      = letter
+                       , Token.identLetter     = alphaNum <|> char '_'
+                       , Token.reservedOpNames = ["[", "]"]
+                       }
+
+type Parser = Parsec String ()
+
+lexer :: Token.GenTokenParser String u Identity
+lexer = Token.makeTokenParser languageDef
+
+identifier :: Parser String
+identifier = Token.identifier lexer
+
+reservedOp :: String -> Parser ()
+reservedOp = Token.reservedOp lexer
+
+parens :: Parser a -> Parser a
+parens = Token.parens lexer
+
+data Expression = Index Int | Abstraction Int Expression | Application Expression Expression
+  deriving (Ord, Eq)
+data Instruction = Define String Expression | Evaluate Expression | Comment String
+
+parseAbstraction :: Parser Expression
+parseAbstraction = do
+  reservedOp "["
+  idc <- endBy1 digit spaces
+  build idc <$> parseExpression
+ where
+  build (idx : idc) body =
+    Abstraction ((read . pure :: Char -> Int) idx) $ build idc body
+  curry [] body = body
+
+parseApplication :: Parser Expression
+parseApplication = do
+  s <- sepBy1 parseSingleton spaces
+  pure $ foldl1 Application s
+
+parseSingleton :: Parser Expression
+parseSingleton = parseAbstraction <|> parens parseApplication
+
+parseExpression :: Parser Expression
+parseExpression = do
+  expr <- parseApplication <|> parseSingleton
+  pure expr
+
+parseDefine :: Parser Instruction
+parseDefine = do
+  var <- identifier
+  space
+  Define var <$> parseExpression
+
+parseLine :: Parser Instruction
+parseLine = try parseDefine
+
+parseReplLine :: Parser Expression
+parseReplLine = try parseExpression