elm-verify

Verify allows you to validate a model into a structure that makes forbidden states impossible.

Example Use-Case

Your model is unvalidated, but on submit you want to verify your model and allow your function to submit that model to only take a verified model.

Your model would maybe look like this:

    type alias Model =
        { id : Int
        , firstName : Maybe String
        , lastName : Maybe String

        -- ...
        }

Your submit function would be: submit : VerifiedModel -> Cmd msg -- not Model

So you define VerifiedModel like this:

    type alias VerifiedModel =
        { id : Int
        , firstName : String
        , lastName : String

        -- ...
        }

and you can verify this by using a Json.Decode.Pipeline-like api.

     Verify.ok VerifiedModel
         |> keep .id
         |> verify .firstName (Maybe.Verify.isJust "error")
         |> verify .lastName (Maybe.Verify.isJust"error")