Some implementations allow arbitrary syntactic keywords to be used as variable names, instead of reserving them, as this report would have it. But this creates ambiguities in the interpretation of expressions: for example, in the following, it's not clear whether the expression (if 1 2 3) should be treated as a procedure call or as a conditional.
These ambiguities are usually resolved in some consistent way within any given implementation, but no particular treatment stands out as being clearly superior to any other, so these situations were excluded for the purposes of this report.
Move cwcc history back here? — Andy Cromarty is concerned about confusion over who the audience is.
Cromarty: 23. NOTES, p.35ff.: This material should stay somehow. We need to make it clear that R3 Scheme is not being touted as Yet Another Ultimate Solution To The Programming Language Problem, but rather as a snapshot of a *process* of good design, for which not all answers have yet been found. We also ought to use the opportunity for publicity afforded us by SIGPLAN to advertise some of the thorny unsolved problems that need further research, and encourage language designers to work on them.