Avoiding ad-hoc with yesod-form
Hello cafe, I have a custom data type: data Foo = Foo | Bar | Baz deriving (Show, Bounded, Enum) In my yesod app I need to have two forms, one that get two Foo and a second that recieve three Foo. From What I've seen online I need to create two new data types: data Foo2 = { foo1 :: Foo, foo2 :: Foo } data Foo3 = { foo1 :: Foo, foo2 :: Foo, foo3 :: Foo } This is tedious and very much ad-hoc. In my actual app it goes up to Foo6 :( Is there a better way to do it? This is how I defined the forms: foo2AForm :: AForm Handler Foo2 foo2AForm = Foo2 <$> areq (selectFieldList foos) "foo1" Nothing <*> areq (selectFieldList foos) "foo2" Nothing where foos:: [(Text, Role)] foos= map (pack . show &&& id) [minBound..] foo2Form :: Html -> MForm Handler (FormResult Foo2, Widget) foo2Form = renderTable teamAForm foo3AForm :: AForm Handler Foo3 foo3AForm = Foo3 <$> areq (selectFieldList foos) "foo1" Nothing <*> areq (selectFieldList foos) "foo2" Nothing <*> areq (selectFieldList foos) "foo3" Nothing where foos:: [(Text, Role)] foos= map (pack . show &&& id) [minBound..] foo3Form :: Html -> MForm Handler (FormResult Foo2, Widget) foo3Form = renderTable teamAForm Thanks
On 2017-07-24 12:54, Yotam Ohad wrote:
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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] where makeFooField :: Int -> AForm Handler Foo makeFooField n = areq (selectFieldList foos) (makeFooName n) Nothing foos :: [(Text, Role)] foos = first tshow . join (,) <$> [minBound..] Note that traverse works on any Traversable (Duh.), and the usual maps are all Traversable, so you can easily adapt this to return, say, a (Map String Foo) or a (Map FooName Foo). And similar methods work for monadic forms. But: The way you asked the question smells like there might be something bad in either the user interface or the structural design. Maybe you want just one form with six fields plus CSS to conditionally hide some of them? Maybe you want one form with n fields plus an additional field to select the n? (Monadic fields should be able to do that.) Maybe there's no real maximum limit so you need just one field generator but a more complex front-end? I'm not saying you're doing it wrong, it's just that my nose is itching. Cheers.
This is how I defined the forms: foo2AForm :: AForm Handler Foo2
foo2AForm = Foo2 <$> areq (selectFieldList foos) "foo1" Nothing <*> areq (selectFieldList foos) "foo2" Nothing where foos:: [(Text, Role)] foos= map (pack . show &&& id) [minBound..]
[…]
Hi, 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@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] where
makeFooField :: Int -> AForm Handler Foo makeFooField n = areq (selectFieldList foos) (makeFooName n) Nothing
foos :: [(Text, Role)] foos = first tshow . join (,) <$> [minBound..]
Note that traverse works on any Traversable (Duh.), and the usual maps are all Traversable, so you can easily adapt this to return, say, a (Map String Foo) or a (Map FooName Foo). And similar methods work for monadic forms.
But: The way you asked the question smells like there might be something bad in either the user interface or the structural design. Maybe you want just one form with six fields plus CSS to conditionally hide some of them? Maybe you want one form with n fields plus an additional field to select the n? (Monadic fields should be able to do that.) Maybe there's no real maximum limit so you need just one field generator but a more complex front-end? I'm not saying you're doing it wrong, it's just that my nose is itching.
Cheers.
This is how I defined the forms: foo2AForm :: AForm Handler Foo2
foo2AForm = Foo2 <$> areq (selectFieldList foos) "foo1" Nothing <*> areq (selectFieldList foos) "foo2" Nothing where foos:: [(Text, Role)] foos= map (pack . show &&& id) [minBound..]
[…]
participants (2)
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MarLinn -
Yotam Ohad