allow reading from stdin

README.md

@@ -60,7 +60,8 @@ running `stack install`, or copy over the executable manually.
 
 sv2v takes in a list of files and prints the converted Verilog to `stdout`.
 Users may specify `include` search paths, define macros during preprocessing,
-and exclude some of the conversions.
+and exclude some of the conversions. Specifying `-` as an input file will read
+from `stdin`.
 
 Below is the current usage printout. This interface is subject to change.
 

src/Language/SystemVerilog/Parser/Lex.x

@@ -527,7 +527,10 @@ alexInitUserState = LS [] "" Map.empty [] [] []
 -- public-facing lexer entrypoint
 lexFile :: [String] -> Env -> FilePath -> IO (Either String ([Token], Env))
 lexFile includePaths env path = do
-    str <- readFile path >>= return . normalize
+    str <-
+        if path == "-"
+            then getContents
+            else readFile path >>= return . normalize
     let result = runAlex str $ setEnv >> alexMonadScan >> get
     return $ case result of
         Left msg -> Left msg