[web-devel] Yesod gotcha (kind of, not sure, it got me good though)

Michael Snoyman michael at snoyman.com
Wed Nov 3 20:46:00 CET 2010

You are absolutely correct that this a problem with Yesod, in
particular Hamlet version 0.5. I specifically released version 0.6 to
make Cassius more flexible and to give better error messages. In
future versions of Yesod, Hamlet 0.5 will be excluded with a version
bound. Unfortunately, doing so during the Yesod 0.6 line would break
the PVP (I think).


On Wed, Nov 3, 2010 at 4:26 PM, Nubis <nubis at woobiz.com.ar> wrote:
> Hi guys,
> I'm fully getting into haskell thanks to the yesod framework. I've been
> pulling my hair with a bug as silly as they come, and for so long that I
> cannot tell it without feeling embarrassed. (I'm working on the
> haskellers.com website code, just to give you some extra context)
> I was getting a 500 in one of my controllers, and I first though there was
> some non existing id being referenced from a model, I set up the haskell
> interactive debugger and launched my yesod project from ghci, single stepped
> and everything looked just fine.
> The actual error displayed was:"Internal Server Error" "A LineSingle must
> have nested content"
> The issue was finally that a cassius file had some trailing garbage (that
> went unnoticed by me, probably added accidentally when passing out over my
> keyboard).
> My main issue with this is that I think of cassius files as just css, I
> wouldn't expect to get an error in my page just for a broken css file. I
> would expect seeing broken styles, or even better, the program not compiling
> at all. I searched for the LineSingle error message and seems to be related
> to hamlet, I interpreted that as a pointer but was in the wrong direction.
> I know this won't happen to me again, but just wanted to throw it out here
> to see if you consider it a gotcha.
> cheers :)
> ----nubis :)
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