"Couldn't match type [...] ("https://www.googleapis.com/auth/datastore" Data.Type.Equality.== "https://www.googleapis.com/auth/datastore") [...] with ‘'True’" about gogol

[rightfold]

I am also experiencing this problem, quite consistently: touch a file that uses this, and it breaks. Clean and rebuild, and it works until you touch the file again.

It seems like it may be a GHC bug related to interface files and type families, but I'm not sure.

[yoricksijsling]

Add the following import to your file to fix this:

import GHC.TypeLits ()

It contains the following bit of code which declares the type instance that is required to compare symbols.

type family EqSymbol (a :: Symbol) (b :: Symbol) where
  EqSymbol a a = 'True
  EqSymbol a b = 'False
type instance a == b = EqSymbol a b

[brendanhay]

Hi @runeksvendsen, I've seen your message but I haven't had time to dig in and provide a clear example. The short version is that class constraints will propagate all the way though the code as you've seen. constraints need to be discharged - and to do that possibly an additional combinator may need to be provided.

[runeksvendsen]

Allow me to shortly summarize what I don't understand, and what leads me to think there's a bug somewhere. The error I receive is:

    • Couldn't match type ‘(("https://www.googleapis.com/auth/datastore"
                             Data.Type.Equality.== "https://www.googleapis.com/auth/cloud-platform")
                            Data.Type.Bool.|| ("https://www.googleapis.com/auth/datastore"
                                               Data.Type.Equality.== "https://www.googleapis.com/auth/datastore"))
                           Data.Type.Bool.|| Network.Google.Auth.Scope.HasScope'
                                               '[]
                                               '["https://www.googleapis.com/auth/cloud-platform",
                                                 "https://www.googleapis.com/auth/datastore"]’
                     with ‘'True’

The second sub-expression in the expression that allegedly doesn't evaluate to 'True is ("https://www.googleapis.com/auth/datastore" Data.Type.Equality.== "https://www.googleapis.com/auth/datastore") which, as far as both GHCi and I can see, should evaluate to 'True.

Please enlighten me here.

[matthew-piziak]

This is a problem for me as well. Cleaning and rebuilding works, but that takes a long time so a workaround would be appreciated.