program is runnable again, File doesn't backtrack out of import anymore

src/Ubc/Parse/Syntax/Import.hs

@@ -54,7 +54,6 @@ parse :: ParsecT String u Transformer Import
 parse = do
         UbcLanguage.reserved "import"
         fragments <- importPath
-        importAs <- option (NonEmpty.last fragments) importAlias
 
         -- concatenate directory and file parts, also utf-decoding
         relFile <- case parseRelPath fragments of
@@ -66,12 +65,16 @@ parse = do
         -- only existing files
         existingFiles <- liftIO $ filterInexistent possiblePaths
 
-        -- fail if there are multiple files
-        case existingFiles of
+        -- fail or parse
+        importedFile <- case existingFiles of
                 [] -> fail $ notFoundMessage relFile possiblePaths
-                [path] -> parseFile path importAs
+                [path] -> parseFile path
                 fs@_ -> fail $ multipleFoundMessage relFile fs
 
+        importAs <- Parsec.parserTraced "alias" $ option (NonEmpty.last fragments) importAlias
+
+        return $ Import importedFile importAs
+
 importAlias :: Monad m => ParsecT String u m String
 importAlias = UbcLanguage.reserved "as" 
         *> UbcLanguage.identifier
@@ -82,12 +85,12 @@ multipleFoundMessage relFile foundFiles = "Could not identify imported file " <>
         <> (unlines . List.map (Path.fromAbsFile >>> ('\t':)) $ foundFiles)
 
 notFoundMessage :: Path Rel File -> [Path Abs File] -> String
-notFoundMessage relFile searchedLocations = "Could not locate import file path" <> Path.fromRelFile relFile <> "\n"
-                <> "Searched locations were:"
+notFoundMessage relFile searchedLocations = "Could not locate import file <" <> Path.fromRelFile relFile <> ">\n"
+                <> "Searched locations were:\n"
                 <> (unlines . List.map (('\t':) . Path.fromAbsFile) $ searchedLocations)
 
-parseFile :: Path Abs File -> String -> ParsecT String u Transformer Import
-parseFile path importAs = do
+parseFile :: Path Abs File -> ParsecT String u Transformer File.File
+parseFile path = do
         let stringPath = Path.fromAbsFile path
         contents <- liftIO . readFile $ stringPath
 
@@ -101,16 +104,21 @@ parseFile path importAs = do
                 >>> (flip Parsec.setSourceColumn) 1
                 $ oldPosition
 
+        -- disable backtracking (consuming input)
+        Parsec.setInput "_" <* Parsec.char '_'
+
         -- prepare new state
         Parsec.setInput contents
         Parsec.setPosition newPosition
-        importedFile <- File.parse stringPath 
+
+        -- parse the file
+        importedFile <- File.parse <* Parsec.eof
 
         -- restore old state
         Parsec.setInput oldInput
         Parsec.setPosition oldPosition
 
-        pure $ Import importedFile importAs
+        pure importedFile 
 
 parseRelPath :: MonadThrow m => NonEmpty FilePath -> m (Path Rel File)
 parseRelPath fragments = do