Implement basic interpreted language

src/Grammar/Abs.hs

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+-- File generated by the BNF Converter (bnfc 2.9.4.1).
+
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+
+-- | The abstract syntax of language Grammar.
+
+module Grammar.Abs where
+
+import Prelude (Integer, String)
+import qualified Prelude as C (Eq, Ord, Show, Read)
+import qualified Data.String
+
+data Program = Program Exp
+  deriving (C.Eq, C.Ord, C.Show, C.Read)
+
+data Exp
+    = EId Ident
+    | EInt Integer
+    | EApp Exp Exp
+    | EAdd Exp Exp
+    | EAbs Ident Exp
+  deriving (C.Eq, C.Ord, C.Show, C.Read)
+
+newtype Ident = Ident String
+  deriving (C.Eq, C.Ord, C.Show, C.Read, Data.String.IsString)
+