Unclear Error Message in Load Table

[josh-torre]

The following program causes an internal error to be thrown:

customer-table = load-table: age, zipcode, income
  source: "data.csv"
end

The resulting error:

Evaluating the object lookup at definitions://:3:17-5:3 errored.

The left side was not an object:
"data.csv"

One or more internal errors prevented us from showing the best error message possible. Please report this as a bug.

This error occurs on any arbitrary source string. The file does not need to exist.

[zackbach]

The "one or more internal errors..." message arises from the render-fancy-reason method failing:

pyret-lang/src/arr/trove/error.arr

Lines 721 to 724 in 33fbaac

	shadow ast = cases(Any) ast:
	| s-dot(_,_,_) => ast
	| s-app(_,f,_) => f
	end

This fails with a no-cases-matched, since the re-parsed chunk of AST at location 3:17-5:3 is an s-load-table, not a s-app or s-dot.

Even if this fancy rendering worked correctly, we still probably want to report a better error message: it is leaking an implementation detail of source: (that being that it desugars to a call to "data.csv".load(...)). Since we have the whole s-load-table at our disposal, a more specialized error message seems possible to report.