add contents to Token

semantic-ast/src/AST/Token.hs

@@ -1 +1,17 @@
-module Token () where
+{-# LANGUAGE DataKinds, DeriveGeneric, DeriveTraversable, KindSignatures #-}
+module AST.Token
+( Token(..)
+) where
+
+import GHC.Generics (Generic, Generic1)
+import GHC.TypeLits (Symbol, Nat)
+
+-- | An AST node representing a token, indexed by its name and numeric value.
+--
+-- For convenience, token types are typically used via type synonyms, e.g.:
+--
+-- @
+-- type AnonymousPlus = Token "+" 123
+-- @
+newtype Token (symName :: Symbol) (symVal :: Nat) a = Token { ann :: a }
+  deriving (Eq, Foldable, Functor, Generic, Generic1, Ord, Show, Traversable)