[Haskell-cafe] Avoiding ad-hoc with yesod-form
yotam2206 at gmail.com
Mon Jul 24 15:28:41 UTC 2017
Thanks, I'm feeling kinda dumb because I forgot this is applicative, but
yet feeling amazed on how great Haskell is to let you do stuff like that.
Your nose may not have betrayed you, I'm using these forms to show rows
from a database with added buttons to manage it from the web. On the other
hand, I might be really bad at explaining my questions
בתאריך יום ב׳, 24 ביולי 2017 ב-15:54 מאת MarLinn <monkleyon at gmail.com
> On 2017-07-24 12:54, Yotam Ohad wrote:
> > […]
> > Is there a better way to do it?
> Yes. AForm is Applicative. So you should just be able to use other
> applicative combinators.
> For example (untested):
> fooAForm :: Int -> AForm Handler [Foo]
> fooAForm count = traverse makeFooField [1..count]
> makeFooField :: Int -> AForm Handler Foo
> makeFooField n = areq (selectFieldList foos) (makeFooName n)
> foos :: [(Text, Role)]
> foos = first tshow . join (,) <$> [minBound..]
> Note that traverse works on any Traversable (Duh.), and the usual maps
> are all Traversable, so you can easily adapt this to return, say, a
> (Map String Foo) or a (Map FooName Foo). And similar methods work for
> monadic forms.
> But: The way you asked the question smells like there might be something
> bad in either the user interface or the structural design. Maybe you
> want just one form with six fields plus CSS to conditionally hide some
> of them? Maybe you want one form with n fields plus an additional field
> to select the n? (Monadic fields should be able to do that.) Maybe
> there's no real maximum limit so you need just one field generator but a
> more complex front-end? I'm not saying you're doing it wrong, it's just
> that my nose is itching.
> > This is how I defined the forms:
> > foo2AForm :: AForm Handler Foo2
> > foo2AForm = Foo2
> > <$> areq (selectFieldList foos) "foo1" Nothing
> > <*> areq (selectFieldList foos) "foo2" Nothing
> > where
> > foos:: [(Text, Role)]
> > foos= map (pack . show &&& id) [minBound..]
> > […]
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