If I have a grandparent, a child component, and a grandchild component, can the grandparent request the state of the child? I've tried using "request" like here but the types don't match up when you're requesting the state of a child that also has a child of its own. The example in the guide works fine when I'm requesting the state of a child that does not have children.
The error is:
Could not match type
Query
with type
Coproduct (Coproduct Query (ChildF AnswerSlot Query)) Query
Yes, definitely. You're probably just missing a left in the query to the child - that's required as the child's query algebra will be of the form Coproduct f (ChildF p f') with it having its own child.
Correspondingly, you can query the grandchild from the grandparent too, by using right and constructing a ChildF with the appropriate values for the grandchild.
I've put together a contrived example of querying both child and grandchild that will hopefully make things clearer:
module Main where
import Prelude
import Data.Functor.Coproduct (Coproduct, left, right)
import Data.Maybe (Maybe(..), fromMaybe)
import Debug.Trace (traceA) -- from purescript-debug
import Halogen as H
import Halogen.HTML as HH
--------------------------------------------------------------------------------
type GrandState = Unit
data GrandQuery a = AskGrandChild (String -> a)
grandchild :: forall g. H.Component GrandState GrandQuery g
grandchild = H.component { render, eval }
where
render :: GrandState -> H.ComponentHTML GrandQuery
render _ = HH.div_ []
eval :: GrandQuery ~> H.ComponentDSL GrandState GrandQuery g
eval (AskGrandChild k) = pure $ k "Hello from grandchild"
--------------------------------------------------------------------------------
type ChildState = Unit
data ChildQuery a = AskChild (String -> a)
type GrandSlot = Unit
type ChildState' g = H.ParentState ChildState GrandState ChildQuery GrandQuery g GrandSlot
type ChildQuery' = Coproduct ChildQuery (H.ChildF GrandSlot GrandQuery)
child :: forall g. Functor g => H.Component (ChildState' g) ChildQuery' g
child = H.parentComponent { render, eval, peek: Nothing }
where
render :: ChildState -> H.ParentHTML GrandState ChildQuery GrandQuery g GrandSlot
render _ = HH.slot unit \_ -> { component: grandchild, initialState: unit }
eval :: ChildQuery ~> H.ParentDSL ChildState GrandState ChildQuery GrandQuery g GrandSlot
eval (AskChild k) = pure $ k "Hello from child"
--------------------------------------------------------------------------------
type ParentState = Unit
data ParentQuery a = Something a
type ChildSlot = Unit
type ParentState' g = H.ParentState ParentState (ChildState' g) ParentQuery ChildQuery' g ChildSlot
type ParentQuery' = Coproduct ParentQuery (H.ChildF ChildSlot ChildQuery')
parent :: forall g. Functor g => H.Component (ParentState' g) ParentQuery' g
parent = H.parentComponent { render, eval, peek: Nothing }
where
render :: ParentState -> H.ParentHTML (ChildState' g) ParentQuery ChildQuery' g ChildSlot
render _ = HH.slot unit \_ -> { component: child, initialState: H.parentState unit }
eval :: ParentQuery ~> H.ParentDSL ParentState (ChildState' g) ParentQuery ChildQuery' g ChildSlot
eval (Something next) = do
-- note the `left` here
childAnswer <- H.query unit $ left $ H.request AskChild
traceA $ fromMaybe "child not found" $ childAnswer
grandAnswer <- H.query unit $ right $ H.ChildF unit $ H.request AskGrandChild
traceA $ fromMaybe "grandchild not found" $ grandAnswer
pure next
