[web-devel] Esqueleto error messages

Felipe Almeida Lessa felipe.lessa at gmail.com
Thu Oct 25 13:41:35 CEST 2012

On Wed, Oct 24, 2012 at 10:32 PM, Erik de Castro Lopo
<mle+hs at mega-nerd.com> wrote:
> Hi all (and in particular Filipe),

Hey! =)

> I'm looking at Esqueleto and I'm finding that in certain circumstances
> it can throw out some rather horrid error messages. Consider the correct
> code fragment taken from the Esqueleto docs:
>     select $
>         from $ \(b, p) -> do
>             where_ (b ^. BlogPostAuthorId ==. p ^. PersonId)
>             return (b, p)
> The error occurs if the programmer uses the wrong identifer in the where_
> clause. For instance, if PersonId is used instead of BlogPostAuthorId
> then I get about 100 lines of error message, the majority of which is
> totally incomprehensible.

What are those messages?

> Is there anything that can be done inside Esqueleto to make these error
> messages better?

Nothing straightforward, AFAIK.  Sadly, the horridness of the error
messages is directly proportional to the amount of type hackery in the

Cheers, =)


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