Clear Include before updateRecord
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Web/Controller/LandingPages.hs
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| @@ -79,6 +72,11 @@ instance Controller LandingPagesController where | |||
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| setSuccessMessage "LandingPage updated" | |||
| redirectTo EditLandingPageAction { .. } | |||
| where | |||
| extractLandingPageFromInclude :: Include' ["paragraphCtas", "paragraphQuotes"] LandingPage -> LandingPage | |||
| extractLandingPageFromInclude landingPage = landingPage | |||
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can you try to split this into two sub functions: one turning Include' ["paragraphCtas", "paragraphQuotes"] LandingPage -> Include' ["paragraphCtas"] LandingPage and then one turning Include' ["paragraphCtas"] LandingPage -> LandingPage ?
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That actually works, which isn't intuitive. a9f132a
Why is that (and how did you figure it might work 😄 )?
Is it somehow related to the fact that the compiler thinks that Include "paragraphQuotes" LandingPage is not equal to Include' ["paragraphQuotes"] LandingPage
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I expected this by intuition 😄 In very early IHP versions updateField was actually set and it was later changed (because it was causing errors like these). The core problem with updateField is, that it's type definition is very open. It's defined as updateField :: value' -> model -> model'. Here model and model' are two independent type variables. This means a call to updateField can actually change the return type of the record (e.g. turning LaindingPage to Include "paragraphQuotes" LandingPage). The problem with your first version was that GHC could not figure out the model' variable because multiple updateField were chained (the model type argument is easy for GHC to figure out, it's just that the model' is independent of that).
For comparison set is defined as set :: value -> model -> model. In that case when GHC can figure out model it will never error. So set is typically easy to figure out and unlikely to error. One the other side the problem with set is that it's less flexible and cannot change the output type (e.g. with model = LandingPage it will be set :: value -> LandingPage -> LandingPage, so there's no way to express e.g. the Include stuff). That's why updateField exists.
TL;DR: updateField has a more open type signature than set and sometimes GHC needs a bit of help
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👌 Thanks for the explanation.
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@mpscholten I've updated Stackoverflow, so this info is not lost :)
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