I've been very hesitant about adding more features to Hamlet, especially ones that are already implemented in Haskell. That's been my reasoning for avoiding any kind of variable definitions until now. However, this does seem like a compelling use case.

I don't think it would make sense to limit it to foralls: it makes as much sense in maybes, and I think it would be confusing if it only applied in some cases. As for syntax, how about:

$forall row <- rs

$let formId = fromMaybe "" $ IntMap.lookup $ getInt "form_id" row

...

I'm not 100% sold on this yet, what does everyone else think?

One last note: I'm probably going to be announcing a feature freeze on Yesod 0.8 *very* soon, and making a beta release to Yackage so that people can test. If you have any last-minute input, now's the time. I'm planning on giving the beta test period about a week, and then releasing to Hackage.

Michael

On Thu, Apr 7, 2011 at 2:57 AM, <vagif.verdi@gmail.com> wrote:

I noticed a pattern that in hamlet $forall i often retrieve the same value
from a map, Sometimes 3,4 times.

$forall row <- rs
<td><a href=@{FormR (getInt "form_id" row)}>#{getStr "form_name"
row}
<td>#{getStr "docname" row}
...
<td>#{fromMaybe "" (IntMap.lookup (getInt "form_id" row)
counties)}
<td>#{fromMaybe "" (IntMap.lookup (getInt "form_id" row)
customers)}

Would it be possible to allow let statement in forall for often used values ?

Regards,
Vagif Verdi

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