Modeling condition, nested forms with elm-simple-forms -

i have form starts select. depending on selected form expands common main bit , details section depends on selection.

i started modeling separate details section

type productdetails     = book book.model     | brochure brochure.model     | card card.model  type alias model =   { form : form customerror estimate   , details : productdetails      -- form customererror cardmodel / bookmodel / ....   , msg : string   } 

but becoming quite convoluted handle in e.g. view.

the alternative seem conditionally add details main form model - e.g.

type alias estimate =   { customer : string   , project : string   , product : string   , details : productdetails   } 

before started i’d welcome experience others on has worked well

if understand correctly, have separate modules book, brochure , card? don't quite understand purpose of model structure this:

import book import brochure import card  type products     = book     | brochure     | card   type msg     = details products   type alias model =     { selectedproduct : product     }   update : msg -> model -> model update msg model =     case msg of         details prd ->             model prd   view : model -> html view model =     model.selectedproduct.view 

so can see, define available products , msg can details, show details, , it's function set selectedproduct value in model selected product. can implement selecting with:

button [ onclick (details book) ] [ text "book" ] 

for example select book. later on want make dynamic , first instinct should able call view function of selected product.

in other case define view require fields, every product's model contain , use them write information on site.

please note code above isn't meant work, it's represent idea.