subdomain kinda works

src/DomainParser.purs

@@ -4,11 +4,12 @@ module DomainParser where
 import Prelude
 --import Prelude (bind, discard, pure, show, ($), (<>), (>))
 
+import Control.Lazy (defer)
 import Data.Maybe (Maybe(..))
 import Data.Array as A
 import Data.String as S
 import Data.Tuple (Tuple(..))
-import Data.Array.NonEmpty as NonEmpty
+-- import Data.Array.NonEmpty as NonEmpty
 import Data.String.CodeUnits as CU
 import Control.Alt ((<|>))
 import Control.Plus (empty)
@@ -42,45 +43,54 @@ parse_last_char s p = case last_char s of
     Nothing -> false
     _       -> true
 
-try :: Parser String -> Parser String
+-- | FIXME: This is flawed.
+-- | We cannot know if it worked: in case there is a problem with the parser `p`,
+-- | the code will "continue to work" but without what's been parsed.
+-- | This may sound reasonable but it prevents knowing if a problem actually occured!
+-- | We cannot do a `try parser <|> alternative` since it will always work!
+try :: forall a. Monoid a => Parser a -> Parser a
 try p = Parser p'
   where p' str = case parse p str of
-                   Nothing -> Just (Tuple "" str) -- FIXME: This is flawed: we cannot know if it worked!
+                   Nothing -> Just (Tuple mempty str) -- FIXME! Need a better base structure.
                    Just x -> pure x
 
 -- From RFC 1035: <label> ::= <letter> [ [ <ldh-str> ] <let-dig> ]
 label :: Parser String
-label = let_then_str_then_alpha <|> (CU.singleton <$> letter)
-  where
-    let_then_str_then_alpha :: Parser String
-    let_then_str_then_alpha = do
-      labelstr <- try do
+label = do
   l <- letter
-        s <- ldh_str
-        pure $ CU.singleton l <> CU.fromCharArray s
-      if (S.length labelstr > label_maxsize || not (parse_last_char labelstr let_dig))
+  s <- try ldh_str
+  let labelstr = CU.singleton l <> CU.fromCharArray s
+  if (S.length labelstr > label_maxsize)
+  then empty
+  else if (S.length labelstr > 1 && not (parse_last_char labelstr let_dig))
        then empty
        else pure labelstr
 
+-- From RFC 1035: <subdomain> ::= <label> | <subdomain> "." <label>
+subdomain :: Parser String
+subdomain = do
+  -- First: read a label. This is bare minimum for a subdomain.
+  lab <- label
+  upperlabels <- try do
+    _ <- char '.'
+    sub <- defer \_ -> subdomain
+    pure sub
+  if (S.length upperlabels == 0) -- This is related to the problem of not having a proper base structure.
+  then pure lab
+  else pure $ lab <> "." <> upperlabels
 
---      Tuple whole_label last_char <- PC.try do
---        pure $ Tuple (CU.singleton l <> (CU.fromCharArray $ NonEmpty.toArray s)) (NonEmpty.last s)
---      case runParser (CU.singleton last_char) let_dig of
---        Left _  -> fail $ "Label is wrong: last char is '" <> (CU.singleton last_char) <> "' which isn't an alphanum"
---        Right _ -> if S.length whole_label > 63 -- Remember: we already did read a letter (l).
---                   then Nothing
---                   else pure whole_label
-
---    let_then_str_then_alpha = do
---      Tuple whole_label last_char <- PC.try do
---        l <- letter
---        s <- ldhstr
---        pure $ Tuple (CU.singleton l <> (CU.fromCharArray $ NonEmpty.toArray s)) (NonEmpty.last s)
---      case runParser (CU.singleton last_char) let_dig of
---        Left _  -> fail $ "Label is wrong: last char is '" <> (CU.singleton last_char) <> "' which isn't an alphanum"
---        Right _ -> if S.length whole_label > 63 -- Remember: we already did read a letter (l).
---                   then fail $ "too big"
---                   else pure whole_label
+----  -- Second: the rest is optional.
+----  r <- PC.optionMaybe (PC.try point_sub)
+----  case r of
+----    Nothing  -> pure lab
+----    Just sub -> pure $ lab <> sub
+----
+----  where
+----    point_sub :: Parser String
+----    point_sub = do
+----      point <- char '.'
+----      sub <- defer \_ -> subdomain
+----      pure $ CU.singleton point <> sub
 
 {-
 import Control.Lazy (defer)
@@ -121,24 +131,6 @@ sub_eof = do
     did_we_parsed_the_final_point Nothing  sub = sub
     did_we_parsed_the_final_point (Just _) sub = sub <> "."
 
--- From RFC 1035: <subdomain> ::= <label> | <subdomain> "." <label>
-subdomain :: Parser String String
-subdomain = do
-  -- First: read a label. This is bare minimum for a subdomain.
-  lab <- label
-  -- Second: the rest is optional.
-  r <- PC.optionMaybe (PC.try point_sub)
-  case r of
-    Nothing  -> pure lab
-    Just sub -> pure $ lab <> sub
-
-  where
-    point_sub :: Parser String String
-    point_sub = do
-      point <- string "."
-      sub <- defer \_ -> subdomain
-      pure $ point <> sub
-
 -- | Converting a single letter parser to a String parser.
 char_to_string :: Parser String Char -> Parser String String
 char_to_string p = do

src/Main.purs

@@ -59,15 +59,41 @@ main = do
   log ""
 
   logtest "label" label "example.org" id
-  logtest "label" label "1notgreat.x" id
-  logtest "label" label ".shouldntwork" id
-  logtest "label" label "a-b.great" id
-  logtest "label" label "-b.shouldfail" id
-  logtest "label" label "b-.shouldfail" id
-  logtest "label" label "toolg.org" id
-  logtest "label" label "too-long.org" id
-  logtest "label" label "too-long-shouldfail.org" id
   logtest "label" label "" id
+  logtest "label" label "a.x" id
+  logtest "label" label "a2.org" id
+  logtest "label" label "a33.org" id
+  logtest "label" label "a444.org" id
+  logtest "label" label "a5555.org" id
+  logtest "label" label "a66666.org" id
+  logtest "label" label "a777777.org" id
+  logtest "label" label "a8888888.org" id
+  log ""
+  logtest "label" label "-" id
+  logtest "label" label "a-" id
+
+  log ""
+
+  logtest "subdomain" subdomain "example.org" id
+  logtest "subdomain" subdomain "" id
+  logtest "subdomain" subdomain "a.x" id
+  logtest "subdomain" subdomain "a2.org" id
+  logtest "subdomain" subdomain "a33.org" id
+  logtest "subdomain" subdomain "a444.org" id
+  logtest "subdomain" subdomain "a5555.org" id
+  logtest "subdomain" subdomain "a66666.org" id
+  logtest "subdomain" subdomain "a777777.org" id
+  logtest "subdomain" subdomain "a8888888.org" id
+  logtest "subdomain" subdomain "xblah.a.x" id
+  logtest "subdomain" subdomain "xblah.a2.org" id
+  logtest "subdomain" subdomain "xblah.a33.org" id
+  logtest "subdomain" subdomain "xblah.a444.org" id
+  logtest "subdomain" subdomain "xblah.a5555.org" id
+  logtest "subdomain" subdomain "xblah.a66666.org" id
+  logtest "subdomain" subdomain "xblah.a777777.org" id
+  logtest "subdomain" subdomain "xblah.a8888888.org" id
+  logtest "subdomain" subdomain "-" id
+  logtest "subdomain" subdomain "a-" id
 
 --  log $ "parsing the first 'f' in 'fiction' (sat): " <> case parse (sat (\x -> x == 'f')) "fiction" of
 --    Just (Tuple x y) -> show x <> " " <> show y