Re: [Haskell-beginners] Re: type def messes up

26 Jun 2010

      On Sunday 27 June 2010 00:35:27, prad wrote:
...
with the
f :: [Tag] -> String
left in ghci croaks:
======
TagSoup.hs:66:14:
    `Tag' is not applied to enough type arguments
    Expected kind `*', but `Tag' has kind `* -> *'
    In the type signature for `f': f :: [Tag] -> String
    In the definition of `ndmPapers':
        ndmPapers = do { tags <- fmap parseTags
                               $ openURL
"http://community.haskell.org/~ndm/downloads/"; let papers = ...;
                           putStr $ unlines papers }
                  where
                      f :: [Tag] -> String
                      f xs = fromTagText (xs !! 2)
Failed, modules loaded: none.
======
(i'm guessing that Tag is some type defined in Text.HTML.TagSoup)
however, the program runs fine if i comment out the type def.
so i'm curious as to why this is so.
Neil changed the kind of Tag in tagsoup-0.8, until version 0.6, it was

data Tag
    = TagOpen String [Attribute]
    | TagClose String
    | TagText String
    | TagComment String
    | TagWarning String
    | TagPosition !Row !Column

and it became

data Tag str
    = TagOpen str [Attribute str]
    | TagClose str
    ...

in 0.8, I think the reason was to allow the use of ByteStrings and 
Data.Text in addition to plain String.

It would also work with

f :: [Tag String] -> String
...
i can't do a :t on f getting a 'not in scope' error, i guess because it
is part of ndmPapers, but that seems strange to me.
It would be very nice if one could query the type of local definitions.

Re: [Haskell-beginners] Re: type def messes up

Daniel Fischer