Error message referring to pattern matching on runtime strings when using Prelude.notYet

[daherb]

When using Prelude.notYet as a placeholder for missing implementations the following error occurs:

- compiling TestConc.gf... Internal error in GeneratePMCFG:
    evalTerm (Predef.error "NOT YET IMPLEMENTED: x")

1) Check that you are not trying to pattern match a /runtime string/.
   These are illegal:
     lin Test foo = case foo.s of {
                       "str" => … } ;   <- explicit matching argument of a lin
     lin Test foo = opThatMatches foo   <- calling an oper that pattern matches

2) Not about pattern matching? Submit a bug report and we update the error message.
     https://github.com/GrammaticalFramework/gf-core/issues

CallStack (from HasCallStack):
  error, called at src/compiler/GF/Compile/GeneratePMCFG.hs:621:13 in gf-3.10.4-EdD6fabQUzM4AhRenbxTb3:GF.Compile.GeneratePMCFG

Minimal grammar;

abstract Test = {
  cat A ;
  fun x : A -> A ;
}

concrete TestConc of Test = open Prelude in {
  lincat
    A = SS ;
  lin
    x = notYet "x" ;
} ;

[daherb]

Recent version compiled from Git

Grammatical Framework (GF) version 3.10.4
Built on linux/x86_64 with ghc-8.6, flags: interrupt server