Custom Type Error not getting triggered in the nested Type function call

[Magesh B]

Hello,

I have partial type function which is invoked by another type function.
When the inner type function fails with TypeError, outer type function is
not been able to propagate that type error to its caller.
As a result of it, I'm getting following error
  • No instance for (KnownSymbol (NestedPartialTF (TypeError ...)))
 instead of
  • Unexpected type @ NestedPartialTF: Char

Is this a bug? This behavior seems bit counter-intuitive as to work around,
I had to write another (duplicate) type function at the top level to get
the desired type error

I'm using GHC-8 RC 3 and have attached complete src for reference.

Regards,
Magesh B
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