John David Stone writes:
The R7RS proposal doesn't include assertions. This creates a needless divergence from R6RS, where the assert syntax is required in the base. One could argue that assertions are an unsuitably blunt instrument for error detection and reporting. Even so, they are useful enough as a teaching tool that I'd like the language to support them.
Assert may yet return; the WG is considering the possibility of an accidental change to a member's ballot that caused ticket #287 on the fifth ballot to fail.
The WG decided not to take action on this, considering it to have been raised untimely.
The WG felt that simple assert is insufficient, and a more complex and useful assertion facility was beyond the scope of the small language. In addition, it is trivial to supply a simple R6RS-compatible assert portably, though non-portable versions may be able to provide better reporting.