[web-devel] [Yesod] widgets in default layout

Michael Snoyman michael at snoyman.com
Mon Feb 21 06:23:56 CET 2011

On Sun, Feb 20, 2011 at 11:04 PM, Dmitry Kurochkin
<dmitry.kurochkin at gmail.com> wrote:
> Hi Michael.
> On Sun, 13 Feb 2011 19:13:06 +0300, Dmitry Kurochkin <dmitry.kurochkin at gmail.com> wrote:
>> On Sun, 13 Feb 2011 17:44:33 +0200, Michael Snoyman <michael at snoyman.com> wrote:
>> > On Sun, Feb 13, 2011 at 5:28 PM, Dmitry Kurochkin
>> > <dmitry.kurochkin at gmail.com> wrote:
>> >
>> > > Still the argument remains. I want to have all menu-related code in a
>> > > separate module.
>> >
>> > OK. As I said, this is possible, and it sounds like you already got
>> > 90% of the way there. I don't know what's holding you up until I see
>> > your code. My initial reaction is still that this is a bad idea in
>> > general, though I *am* reconsidering that position. It might make
>> > sense to alter the approach used by the scaffolded site.
>> >
>> I will try to send you some an example later. Unfortunately, I do not
>> have time for this right now. Playing with Yesod in my free time only.
> I took another look at it. Turns out my problem was caused by using
> getCurrentRoute in the widget. If there is no getCurrentRoute, it works
> fine and I can use the widget in the defaultLayout.
> Here is a simple code to demonstrate the issue:
>    testWidget :: GWidget sub Test ()
>    testWidget = do
>        Just route <- lift getCurrentRoute
>        addWidget [$hamlet|@{route}|]
> Add the above code to the main application module. In the above case
> Test is the foundation type. I get the following error:
>    Couldn't match expected type `TestRoute'
>           against inferred type `Route sub'
>      NB: `Route' is a type function, and may not be injective
> I would appreciate if you explain what the problem is and how to solve
> it.

getCurrentRoute[1] returns a route for the current subsite, while you
want a route for Test (ie, Route sub vs Route Test). You need to
convert your Route sub into a Route Test, by using


[1] http://hackage.haskell.org/packages/archive/yesod-core/
[2] http://hackage.haskell.org/packages/archive/yesod-core/

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