[Haskell-cafe] problems building hpodder

[gwern0 at gmail.com]

On 2008.04.07 00:24:10 +0200, Karl Hasselström <kha-list-haskell-cafe at hemma.treskal.com> scribbled 0.9K characters:
> I'm trying to build hpodder 1.1.2 with ghc 6.8.2. I successfully
> downloaded, built, and installed (the latest versions of) all its
> dependencies, but when building hpodder itself, I get
>
> FeedParser.hs:146:26:
>     `Content' is not applied to enough type arguments
>     Expected kind `??', but `Content' has kind `* -> *'
>     In the type `Content -> Either String String'
>     In the type `String -> Content -> Either String String'
>     In the type signature for `strof_either':
>       strof_either :: String -> Content -> Either String String
>
> I don't know enough Haskell to even determine what kind of problem
> this is -- wrong version of some dependency? Wrong version of ghc?
> Help appreciated. :-)
>
> ( FWIW, the hackage auto-builder thingie seems to have the exact same
>   problem I have:
> http://hackage.haskell.org/packages/archive/hpodder/1.1.2/logs/failure/ghc-6.8
> )
>
> --
> Karl Hasselström, kha at treskal.com

The issue here isn't GHC, but I think it's the former.

If we open up the FeedParser.hs file, we see that the problem is that the type being inferred from what the code does clashes with the type gotten from what the code says. The issue is this Content type.

A quick search shows that Content isn't defined in FeedParser.hs, and so if we comment out imports, we find that Content is coming from Text.XML.HaXml, and is documented here: <http://hackage.haskell.org/packages/archive/HaXml/1.19.2/doc/html/Text-XML-HaXml-Types.html#t%3AContent>.

So almost certainly the issue is that HaXml has updated and changed things around in a way that broke Hpodder; not surprising, since HaXml-1.19.2 is as recent as 14 January 2008, and Goerzen may simply not have updated and discovered the error before he released Hpodder in February.

If the problem is too-recent HaXml, there's an obvious work around. You could install HaXml-1.13.3 <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HaXml-1.13.3> and edit the hpodder.cabal file to replace the 'HaXml>=' bit with 'HaXml==1.13.3'. That works for me.

--
gwern
Etacs FOSS NTIS SUPIR mindwar NATOA SARA niche DNR 3B2
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