Re: [Haskell-beginners] Options for creating a multiple select form via Yesod

Thank you David. I'm trying to figure out step-by-step, exactly how selectFields binds field values. One thing I'm having trouble with is visualizing return values. Beginning with askParams. askParams :: Monad m => StateT Ints (ReaderT Env m) Env askParams = lift askenv <- askParams Here's the example from selectFields env <- askParams later on env is used in with the lookup function let res = case lookup name env of seeing as lookup is checking for value of type a in a [(a,b)] and given the type of askParams I have no idea what is going on here. I don't see a [(a,b)] in askParams :: Monad m => StateT Ints (ReaderT Env m) Env. So if someone could answer how env <- askParams yields a [(a,b)] for lookup to use as input, I would appreciate it. On Mon, Jun 13, 2011 at 2:54 PM, David McBride wrote:

The read function is sort of the opposite of the show function.  Take a string, give me a value.  reads is like read, however it has some traits that read doesn't have.

The problem with read is that if you go: read "asdf" :: Int, it will die with an exception, and that is something you don't want in a web app.  Also it doesn't tell you what the rest of the string is, so you have no real way of finding out what was left of the string after the part you wanted to parse.

So there is the reads function that returns [(a,String)] which is a list of pairs of the answer a, and the rest of the string String.  As a bonus, it returns a list so if it can't parse the string you pass it, then it just returns an empty list.  Why didn't it use Maybe you ask?  I bet it probably has to do with the function being one of the first functions ever written for haskell, long before Maybe existed.

So all it is there is unpack this bytestring into a string, then parse it into a value, and please don't blow up if the input is invalid.

On Mon, Jun 13, 2011 at 5:28 PM, Michael Litchard wrote:

...

I was a bit hasty. I can render a multi-select field easily enough. However, I'm having difficulty following how selectField makes a value from the select field accessible from the handler code calling selectField. Once I figure that out, I can modify multiSelectField accordingly.

The goal here being to modify selectField so that a list of field values can be bound .

Here's what I have so far: multiSelectField is thus far identical in every way to selectField save for the following change in the Hamlet part.

<select multiple="#{theId}" id="#{theId}" name="#{name}">

My thinking was that the value bound to multiple was arbitary, and I'd use theId until I figured out something that made more sense.

Here's where I am focusing my efforts next

http://hpaste.org/47774

Specifically (x', _):_ ->                            case lookup x' pairs' of                                Nothing -> FormFailure ["Invalid entry"]                                Just (y, _) -> FormSuccess y I'm thinking this is where selectField binds a value from the select field form. I'm confused by the (x',_):_. At first I thought it meant that just the first pair in a list of pairs is pattern matched against, and the rest discarded. But then I ask myself where the list is coming from. In a select field there would only be one pair, not a list of them. Here's where I get confused. Because if this is not where the values of the select field get bound, I don't know where it's happening.

Is my confusion clear enough such that I could get some clarifying feedback? If not, what is unclear?

On Sat, Jun 11, 2011 at 11:03 AM, Michael Snoyman wrote:

...

The best way for code contributions in general is to submit a pull request on Github. If that's a problem, sending a patch via email works as well (either directly to me or to web-devel).

Michael

On Sat, Jun 11, 2011 at 1:14 AM, Michael Litchard wrote:

...

Hey! I just added multiSelectField to the Forms library. I'm only getting the first value selected, but I think that's because of how I'm using multiSelecrField. I'm going to try to change the client code to fix this. I'll let you know how it goes. when I get a maybeMultiSelectField added I'll show you what I have. What would be the best way to submit this?

On Thu, Jun 9, 2011 at 10:05 PM, Michael Snoyman wrote:

...

Hi Michael,

There's nothing jQuery or Javascript specific about a multi-select field: it's just a normal select field with a "multiple" attribute. I would recommend taking the selectField code from yesod-form and modifying it to be multi-select. I'll likely do this myself eventually, but it could be a good learning experience in Yesod (and a great introduction to contributing to the framework if you're so inclined).

Michael

On Thu, Jun 9, 2011 at 8:29 PM, Michael Litchard wrote:

...

I'm trying to create a multiple select form, as illustrated on the following: http://api.jquery.com/selected-selector/

Here's the options I see possible:

(1) Write a jQuery widget. (2) Use plain javascript via Julius (3) Use the low-level functions in Yesod.Form to write a widget (4) Use a pre-existing function that does what I need, but am not aware of this functionality

(1) has appeal as it looks like something small I can contribute to the project. It will take me some extra time to figure out the details. But, I had a look at the other jQuery widgets and they seem to provide an approachable model to follow.

(2) This looks like the most straight-forward approach. I'm just learning javascript so would have to figure out how to capture values in Haskell from the form.

(3) This looks like the most difficult way. I don't think I know enough about the low-level functions in Yesod.Form to be able to accomplish this in a timely manner.

(4) This is the best scenario. There's already a way to do this right now, and I just haven't identified it. If this is the case, I would appreciate being pointed in the right direction.

Until informed otherwise, I'm evaluating options 1 and 2. All feedback welcomed. Thanks to all who made Yesod possible.

_______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

_______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

_______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners