From 416c384a981593005c9c6bf87ac27b7c2f9b8695 Mon Sep 17 00:00:00 2001 From: Łukasz Hanuszczak Date: Sun, 21 Jun 2015 23:48:03 +0200 Subject: Add some documentation for parser module of source hyperlinker. --- .../src/Haddock/Backends/Hyperlinker/Parser.hs | 39 ++++++++++++++++++++++ 1 file changed, 39 insertions(+) (limited to 'haddock-api/src') diff --git a/haddock-api/src/Haddock/Backends/Hyperlinker/Parser.hs b/haddock-api/src/Haddock/Backends/Hyperlinker/Parser.hs index 7f408165..6e195dba 100644 --- a/haddock-api/src/Haddock/Backends/Hyperlinker/Parser.hs +++ b/haddock-api/src/Haddock/Backends/Hyperlinker/Parser.hs @@ -40,9 +40,20 @@ data TokenType | TkUnknown deriving (Eq) +-- | Turn source code string into a stream of more descriptive tokens. +-- +-- Result should retain original file layout (including comments, whitespace, +-- etc.), i.e. the following "law" should hold: +-- +-- @concat . map 'tkValue' . 'parse' = id@ parse :: String -> [Token] parse = tokenize . tag . chunk +-- | Split raw source string to more meaningful chunks. +-- +-- This is the initial stage of tokenization process. Each chunk is either +-- a comment (including comment delimiters), a whitespace string, preprocessor +-- macro (and all its content until the end of a line) or valid Haskell lexeme. chunk :: String -> [String] chunk [] = [] chunk str@(c:_) @@ -56,6 +67,11 @@ chunk str where chunk' (c, rest) = c:(chunk rest) +-- | Split input to "first line" string and the rest of it. +-- +-- Ideally, this should be done simply with @'break' (== '\n')@. However, +-- Haskell also allows line-unbreaking (or whatever it is called) so things +-- are not as simple and this function deals with that. spanToNewline :: String -> (String, String) spanToNewline [] = ([], []) spanToNewline ('\\':'\n':str) = @@ -66,6 +82,16 @@ spanToNewline (c:str) = let (str', rest) = spanToNewline str in (c:str', rest) +-- | Split input to whitespace string, (optional) preprocessor directive and +-- the rest of it. +-- +-- Again, using something like @'span' 'isSpace'@ would be nice to chunk input +-- to whitespace. The problem is with /#/ symbol - if it is placed at the very +-- beginning of a line, it should be recognized as preprocessor macro. In any +-- other case, it is ordinary Haskell symbol and can be used to declare +-- operators. Hence, while dealing with whitespace we also check whether there +-- happens to be /#/ symbol just after a newline character - if that is the +-- case, we begin treating the whole line as preprocessor macro. spanSpaceOrCpp :: String -> (String, Maybe String, String) spanSpaceOrCpp ('\n':'#':str) = let (str', rest) = spanToNewline str @@ -76,6 +102,10 @@ spanSpaceOrCpp (c:str') in (c:space, mcpp, rest) spanSpaceOrCpp str = ("", Nothing, str) +-- | Split input to comment content (including delimiters) and the rest. +-- +-- Again, some more logic than simple 'span' is required because of Haskell +-- comment nesting policy. chunkComment :: Int -> String -> (String, String) chunkComment _ [] = ("", "") chunkComment depth ('{':'-':str) = @@ -90,6 +120,7 @@ chunkComment depth (e:str) = let (c, rest) = chunkComment depth str in (e:c, rest) +-- | Assign source location for each chunk in given stream. tag :: [String] -> [(Span, String)] tag = reverse . snd . foldl aux (Position 1 1, []) @@ -100,6 +131,7 @@ tag = move pos '\n' = pos { posRow = posRow pos + 1, posCol = 1 } move pos _ = pos { posCol = posCol pos + 1 } +-- | Turn unrecognised chunk stream to more descriptive token stream. tokenize :: [(Span, String)] -> [Token] tokenize = map aux @@ -110,6 +142,13 @@ tokenize = , tkSpan = sp } +-- | Classify given string as appropriate Haskell token. +-- +-- This method is based on Haskell 98 Report lexical structure description: +-- https://www.haskell.org/onlinereport/lexemes.html +-- +-- However, this is probably far from being perfect and most probably does not +-- handle correctly all corner cases. classify :: String -> TokenType classify str | "--" `isPrefixOf` str = TkComment -- cgit v1.2.3