Corner case in @formula parsing

[bkamins]

julia> @formula(return ~ dkr + eps + nentinc + salary)
ERROR: LoadError: ArgumentError: expected formula separator ~, got return

(real life case from Wooldridge 7e)

[bkamins]

Also:

julia> @formula(price ~ bdrms + identity(sqrft - 150.0 * bdrms))
┌ Warning: Number 150.0 removed from interaction term 150.0 & bdrms
└ @ StatsModels C:\Users\bogum\.julia\packages\StatsModels\fK0P3\src\formula.jl:158
FormulaTerm
Response:
  price(unknown)
Predictors:
  bdrms(unknown)
  (sqrft,bdrms)->identity(sqrft - 150.0bdrms)

(the warning is incorrect as we protected * with identity)

[kleinschmidt]

Ah yeah that's a tricky one. We might need to require that formula expressions don't contain reserved symbols. You could manually construct it with Term("return") of necessary.

The second one may be fixed on master if you're feeling brave! And on master, protect does the thing that identity does in your example...