Unbound binding forms give bad error messages

[Joe Near]

Perhaps this isn't a bug, since evaluation order is unspecified. But when I have written a macro that expands into a binding form (such as exists in miniKanren), and forget to load it, I get a very misleading error message. For example:

joenear@aybars ~ $ ikarus
Ikarus Scheme version 0.0.3+ (revision 1492, build 2008-05-30)
Copyright (c) 2006-2008 Abdulaziz Ghuloum
> fluid-let
Unhandled exception
 Condition components:
   1. &assertion
   2. &who: eval
   3. &message: "unbound variable"
   4. &irritants: (fluid-let)
> (fluid-let ((x 5)) x)
Unhandled exception
 Condition components:
   1. &assertion
   2. &who: eval
   3. &message: "unbound variable"
   4. &irritants: (x)
>

I expected to see that fluid-let was unbound, not that x was. Chez gives a more helpful message:

joenear@aybars ~ $ petite
Petite Chez Scheme Version 7.3
Copyright (c) 1985-2006 Cadence Research Systems

> (luid-let ((x 5)) x)

Error: variable luid-let is not bound.
Type (debug) to enter the debugger.
>

(fluid-let has been changed to luid-let since Chez has fluid-let).