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On 11-Apr-06, at 6:29 PM, Taylor R. Campbell wrote:
Since `:' is a special initial, it is also an initial, and transitively also a subsequent; it may therefore be used at the end of an identifier, according to the rule for <identifier>.
Ouch! You are right. And somehow I still didn't see this after triple checking. Must have been one of those days. For the record Gambit's reader allows colons anywhere in a symbol except the end.
So this means that the prefix and postfix syntaxes are equally non R5RS conformant. Nevertheless I have rarely seen the colon used at the end of an identifier, except when the identifier is used similarly to what keyword objects are used for (i.e. it is used as data, not as a variable name). So changing the type of foo: from symbol to keyword will likely have little effect on such programs.