diff --git a/elsa.cabal b/elsa.cabal
--- a/elsa.cabal
+++ b/elsa.cabal
@@ -1,5 +1,5 @@
 name:                elsa
-version:             0.2.0.1
+version:             0.2.1.0
 synopsis:            A tiny language for understanding the lambda-calculus
 description:         elsa is a small proof checker for verifying sequences of
                      reductions of lambda-calculus terms. The goal is to help
diff --git a/src/Language/Elsa/Eval.hs b/src/Language/Elsa/Eval.hs
--- a/src/Language/Elsa/Eval.hs
+++ b/src/Language/Elsa/Eval.hs
@@ -6,7 +6,7 @@
 import qualified Data.HashSet         as S
 import qualified Data.List            as L
 import           Control.Monad.State
-import           Data.Maybe           (mapMaybe, isJust, maybeToList)
+import qualified Data.Maybe           as Mb -- (isJust, maybeToList)
 import           Language.Elsa.Types
 import           Language.Elsa.Utils  (traceShow, qPushes, qInit, qPop, fromEither)
 
@@ -74,7 +74,7 @@
 -- | Transitive Reachability
 --------------------------------------------------------------------------------
 isTrnsEq :: Env a -> Expr a -> Expr a -> Bool
-isTrnsEq g e1 e2 = isJust (findTrans (isEquiv g e2) (canon g e1))
+isTrnsEq g e1 e2 = Mb.isJust (findTrans (isEquiv g e2) (canon g e1))
 
 isUnTrEq :: Env a -> Expr a -> Expr a -> Bool
 isUnTrEq g e1 e2 = isTrnsEq g e2 e1
@@ -137,8 +137,8 @@
 newAId :: Int -> Id
 newAId n = aId ++ show n
 
-isAId :: Id -> Maybe Int
-isAId x
+_isAId :: Id -> Maybe Int
+_isAId x
   | L.isPrefixOf aId x = Just . read . drop 2 $ x
   | otherwise          = Nothing
 
@@ -164,7 +164,7 @@
 betas (ELam b e z)   = [ ELam b e' z | e' <- betas e ]
 betas (EApp e1 e2 z) = [ EApp e1' e2 z | e1' <- betas e1 ]
                     ++ [ EApp e1 e2' z | e2' <- betas e2 ]
-                    ++ maybeToList (beta e1 e2)
+                    ++ Mb.maybeToList (beta e1 e2)
 
 beta :: Expr a -> Expr a -> Maybe (Expr a)
 beta (ELam (Bind x _) e _) e' = substCA e x e'
@@ -220,8 +220,6 @@
 bSubst e x e' = subst e (M.singleton x e'')
   where
     e''       = e' -- alphaShift n e'
-    n         = 1 + maximum (0 : mapMaybe isAId vs)
-    vs        = S.toList (freeVars e')
 
 --------------------------------------------------------------------------------
 -- | General Helpers
diff --git a/src/Language/Elsa/Parser.hs b/src/Language/Elsa/Parser.hs
--- a/src/Language/Elsa/Parser.hs
+++ b/src/Language/Elsa/Parser.hs
@@ -1,16 +1,23 @@
+{-# LANGUAGE FlexibleInstances #-}
+
 module Language.Elsa.Parser
   ( parse
   , parseFile
   ) where
 
-import           Control.Monad (void)
+import qualified Control.Exception          as Ex
+import           Control.Monad          (void)
 import           Text.Megaparsec hiding (parse)
-import           Text.Megaparsec.String
-import qualified Text.Megaparsec.Lexer as L
+import qualified Text.Megaparsec.Char.Lexer as L
+import           Text.Megaparsec.Char
+import           Text.Megaparsec.Stream ()
 import qualified Data.List as L
 import           Language.Elsa.Types
 import           Language.Elsa.UX
+import           Data.List.NonEmpty         as NE
 
+type Parser = Parsec SourcePos Text
+
 --------------------------------------------------------------------------------
 parse :: FilePath -> Text -> SElsa
 --------------------------------------------------------------------------------
@@ -18,15 +25,26 @@
 
 parseWith  :: Parser a -> FilePath -> Text -> a
 parseWith p f s = case runParser (whole p) f s of
-                    Left err -> panic (show err) (posSpan . errorPos $ err)
+                    Left pErrs -> Ex.throw (mkErrors pErrs) -- panic (show err) (posSpan . NE.head . errorPos $ err)
                     Right e  -> e
 
-instance Located ParseError where
-  sourceSpan = posSpan . errorPos
 
-instance PPrint ParseError where
-  pprint = show
+mkErrors :: ParseErrorBundle Text SourcePos -> [UserError]
+mkErrors b = [ mkError (parseErrorPretty e) (sp b) | e <- NE.toList (bundleErrors b)]
+  where 
+    sp     = posSpan . pstateSourcePos . bundlePosState
 
+instance ShowErrorComponent SourcePos where
+  showErrorComponent = show
+ 
+
+-- panic msg sp = throw [Error msg sp]
+-- instance Located (ParseError SourcePos Text) where
+--  sourceSpan = posSpan . errorPos
+
+-- instance PPrint (ParseError SourcePos Text) where
+--   pprint = show
+
 --------------------------------------------------------------------------------
 parseFile :: FilePath -> IO SElsa
 --------------------------------------------------------------------------------
@@ -92,7 +110,7 @@
 
 identChar :: Parser Char
 identChar =  alphaNumChar
-         <|> oneOf "_#'"
+         <|> oneOf ['_', '#', '\'']
 
 -- | `binder` parses BareBind, used for let-binds and function parameters.
 binder :: Parser SBind
@@ -100,16 +118,16 @@
 
 withSpan' :: Parser (SourceSpan -> a) -> Parser a
 withSpan' p = do
-  p1 <- getPosition
+  p1 <- getSourcePos
   f  <- p
-  p2 <- getPosition
+  p2 <- getSourcePos
   return (f (SS p1 p2))
 
 withSpan :: Parser a -> Parser (a, SourceSpan)
 withSpan p = do
-  p1 <- getPosition
+  p1 <- getSourcePos
   x  <- p
-  p2 <- getPosition
+  p2 <- getSourcePos
   return (x, SS p1 p2)
 
 --------------------------------------------------------------------------------
diff --git a/src/Language/Elsa/Types.hs b/src/Language/Elsa/Types.hs
--- a/src/Language/Elsa/Types.hs
+++ b/src/Language/Elsa/Types.hs
@@ -7,7 +7,6 @@
 
 import           GHC.Generics
 import           Text.Printf (printf)
-import           Data.Monoid
 import           Language.Elsa.UX
 import           Data.Maybe (mapMaybe)
 import           Data.Hashable
diff --git a/src/Language/Elsa/UX.hs b/src/Language/Elsa/UX.hs
--- a/src/Language/Elsa/UX.hs
+++ b/src/Language/Elsa/UX.hs
@@ -38,12 +38,9 @@
 
 import           Control.Exception
 import           Data.Typeable
-import           Data.Monoid
 import qualified Data.List as L
 import           Text.Printf (printf)
 import           Text.Megaparsec
-import           Text.Megaparsec.Pos
--- import           Text.JSON.Pretty
 import           Text.JSON hiding (Error)
 import           Language.Elsa.Utils
 
@@ -70,6 +67,9 @@
   }
   deriving (Eq, Show)
 
+instance Semigroup SourceSpan where
+  x <> y = mappendSpan x y 
+
 instance Monoid SourceSpan where
   mempty  = junkSpan
   mappend = mappendSpan
@@ -94,10 +94,10 @@
 spanInfo s = (f s, l1 s, c1 s, l2 s, c2 s)
   where
     f      = spanFile
-    l1     = sourceLine   . ssBegin
-    c1     = sourceColumn . ssBegin
-    l2     = sourceLine   . ssEnd
-    c2     = sourceColumn . ssEnd
+    l1     = unPos . sourceLine   . ssBegin
+    c1     = unPos . sourceColumn . ssBegin
+    l2     = unPos . sourceLine   . ssEnd
+    c2     = unPos . sourceColumn . ssEnd
 
 --------------------------------------------------------------------------------
 -- | Source Span Extraction
@@ -263,8 +263,8 @@
 
 instance JSON SourcePos where
   readJSON    = undefined
-  showJSON sp = jObj [ ("line"  , showJSON l)
-                     , ("column", showJSON c)
+  showJSON sp = jObj [ ("line"  , showJSON (unPos l))
+                     , ("column", showJSON (unPos c))
                      ]
     where
       l       = sourceLine   sp
diff --git a/src/Language/Elsa/Utils.hs b/src/Language/Elsa/Utils.hs
--- a/src/Language/Elsa/Utils.hs
+++ b/src/Language/Elsa/Utils.hs
@@ -4,7 +4,6 @@
 import qualified Data.List           as L
 import qualified Data.Dequeue        as Q
 import           Data.Hashable
-import           Data.Monoid
 import           Data.Char (isSpace)
 import           Control.Exception
 import           Text.Printf