Reflect the distinction between eval and run from State monad into the Parser module

src/PDF.hs

@@ -21,7 +21,7 @@ import PDF.Object (
   )
 import qualified PDF.Output as Output (render, line)
 import PDF.Output (Output(..))
-import PDF.Parser (Parser, runParser, string, takeAll)
+import PDF.Parser (Parser, evalParser, string, takeAll)
 import Text.Printf (printf)
 
 data Document = Document {
@@ -83,7 +83,7 @@ findNextSection offset input =
 
 readStructures :: Int -> ByteString -> Either String [InputStructure]
 readStructures startXref input =
-  runParser structure () (BS.drop startXref input) >>= stopOrFollow
+  evalParser structure () (BS.drop startXref input) >>= stopOrFollow
   where
     stopOrFollow s@(Structure {trailer}) =
       case Map.lookup (Name "Prev") trailer of
@@ -96,7 +96,7 @@ readStructures startXref input =
 
 parseDocument :: ByteString -> Either String Document
 parseDocument input = do
-  (pdfVersion, eolStyle) <- runParser ((,) <$> version <*> EOL.parser) () input
+  (pdfVersion, eolStyle) <- evalParser ((,) <$> version <*> EOL.parser) () input
   startXref <- readStartXref eolStyle input
   structuresRead <- readStructures startXref input
   let updates = populate input <$> structuresRead

src/PDF/Body.hs

@@ -18,7 +18,7 @@ import PDF.Object (
     , blank, dictionary, directObject, integer, line
   )
 import PDF.Output (ObjectId(..), Offset(..))
-import PDF.Parser (Parser, (<?>), block, char, on, option, runParser, takeAll)
+import PDF.Parser (Parser, (<?>), block, char, evalParser, on, option, takeAll)
 
 data UserState = UserState {
       input :: ByteString
@@ -109,7 +109,7 @@ occurrence =
 populate :: ByteString -> InputStructure -> Content
 populate input structure =
   let bodyInput = BS.drop (startOffset structure) input in
-  case runParser recurseOnOccurrences initialState bodyInput of
+  case evalParser recurseOnOccurrences initialState bodyInput of
     Left _ -> Content {occurrences = [], objects = Map.empty, docStructure}
     Right finalState ->
       let Flow {occurrencesStack, tmpObjects} = flow finalState in

src/PDF/Parser.hs

@@ -13,6 +13,7 @@ module PDF.Parser (
     , oneOf
     , option
     , runParser
+    , evalParser
     , sepBy
     , string
     , takeAll
@@ -80,9 +81,11 @@ oneOf charSet = lift $ Atto.satisfy (`elem` charSet)
 option :: a -> Parser s a -> Parser s a
 option defaultValue p = p <|> pure defaultValue
 
-runParser :: Parser s a -> s -> ByteString -> Either String a
+runParser :: Parser s a -> s -> ByteString -> Either String (a, s)
-runParser parser initState =
+runParser parser initState = Atto.parseOnly (runStateT parser initState)
-  Atto.parseOnly (evalStateT parser initState)
+
+evalParser :: Parser s a -> s -> ByteString -> Either String a
+evalParser parser initState = Atto.parseOnly (evalStateT parser initState)
 
 sepBy :: Parser s a -> Parser s b -> Parser s [a]
 sepBy parser separator =