diff --git a/Debug/Vampire/Rewrite.hs b/Debug/Vampire/Rewrite.hs
new file mode 100644
--- /dev/null
+++ b/Debug/Vampire/Rewrite.hs
@@ -0,0 +1,28 @@
+module Debug.Vampire.Rewrite (rewriteFile) where
+
+import Language.Haskell.Exts
+import Data.Generics.Uniplate.Data (descend, descendBi)
+
+rewriteFile :: String -> Maybe String
+rewriteFile code =
+  case parse code :: ParseResult Module of
+    ParseOk mod -> Just $ prettyPrint $ addHeader $ descendBi rewrite mod
+    _           -> Nothing
+
+addHeader :: Module -> Module
+addHeader (Module loc name prag warn exports imports decls) =
+  Module loc name (implicit:prag) warn exports (trace:imports) decls
+    where implicit = LanguagePragma (SrcLoc {srcFilename = "<unknown>.hs", srcLine = 1, srcColumn = 1}) [Ident "ImplicitParams"]
+          trace    = ImportDecl {importLoc = SrcLoc {srcFilename = "<unknown>.hs", srcLine = 5, srcColumn = 1}, importModule = ModuleName "Debug.Vampire.Trace", importQualified = False, importSrc = False, importPkg = Nothing, importAs = Nothing, importSpecs = Nothing}
+
+-- TODO: replace ugly pasted literal with something more sensible
+rewrite :: Exp -> Exp
+rewrite exp = Let (BDecls [PatBind (SrcLoc {srcFilename = "<unknown>.hs", srcLine = 1, srcColumn = 5}) (PVar (Ident "vResultStruct")) Nothing (UnGuardedRhs (App (Var (UnQual (Ident "vNewExprStruct"))) (Lit (String (prettyPrint exp))))) (BDecls []),PatBind (SrcLoc {srcFilename = "<unknown>.hs", srcLine = 2, srcColumn = 5}) (PVar (Ident "vResult")) Nothing (UnGuardedRhs (Paren (Let (BDecls [PatBind (SrcLoc {srcFilename = "<unknown>.hs", srcLine = 2, srcColumn = 21}) (PVar (Ident "?vCtx")) Nothing (UnGuardedRhs (Var (UnQual (Ident "vResultStruct")))) (BDecls [])]) (descend rewrite exp)))) (BDecls [])]) (App (App (App (Var (UnQual (Ident "vLog"))) (Var (UnQual (Ident "?vCtx")))) (Var (UnQual (Ident "vResult")))) (Var (UnQual (Ident "vResultStruct"))))
+
+{-
+rewrite expr = AST for this:
+  let resultStruct = newExprStruct
+      result = (let ?ctx = resultStruct in [splice expr in])
+  in (log ?ctx result resultStruct) `seq` result
+-}
+
diff --git a/Main.hs b/Main.hs
--- a/Main.hs
+++ b/Main.hs
@@ -1,16 +1,35 @@
 module Main where
 
 import Debug.Vampire
-import System.Environment
-import Data.Functor
+import Options.Applicative
+import Control.Applicative
+import Control.Monad
+import System.Exit
 
-main = do
-  args <- getArgs
-  case args of
-    fn:_ -> do
-      newCode <- rewriteFile <$> readFile fn
-      case newCode of
-        Just code -> putStrLn code
-        Nothing -> putStrLn "Invalid syntax in file!"
-    [] -> putStrLn "Need a filename!"
+readFrom "-"  = getContents
+readFrom file = readFile file
+writeTo  "-"  = putStrLn
+writeTo  file = writeFile file
+
+doRewrite :: String -> String -> IO ()
+doRewrite src dest = do
+  code <- readFrom src
+  case rewriteFile code of
+    Just newCode -> writeTo dest newCode
+    Nothing      -> putStrLn "could not parse input" >> exitFailure
+
+-- parsers!
+
+rewrite =
+  liftA2 doRewrite
+    (argument str $ metavar "SOURCE")
+    (argument str $ metavar "DEST" <> value "-" <> showDefault)
+rewriteDesc = "Rewrite a Haskell source file to add Vampire tracing."
+ 
+vampire = subparser $
+  (command "rewrite" $ info rewrite $ progDesc rewriteDesc)
+
+main = join $ execParser $
+  info (helper <*> vampire)
+  (fullDesc <> header "vampire - eeevil expression tree analysis")
 
diff --git a/vampire.cabal b/vampire.cabal
--- a/vampire.cabal
+++ b/vampire.cabal
@@ -10,7 +10,7 @@
 -- PVP summary:      +-+------- breaking API changes
 --                   | | +----- non-breaking API additions
 --                   | | | +--- code changes with no API change
-version:             0.1.0.0
+version:             0.1.1.0
 
 -- A short (one-line) description of the package.
 synopsis:            Analyze and visualize expression trees.
@@ -55,6 +55,7 @@
 
   other-modules:
     Debug.Vampire.Data
+    Debug.Vampire.Rewrite
     Debug.Vampire.Visualize
 
   build-depends:
@@ -65,7 +66,8 @@
     fgl,
     mtl,
     dlist,
-    graphviz
+    graphviz,
+    optparse-applicative
 
   default-language:    Haskell2010
 
@@ -88,7 +90,8 @@
     fgl,
     mtl,
     dlist,
-    graphviz
+    graphviz,
+    optparse-applicative
   
   -- Directories containing source files.
   -- hs-source-dirs: