> SRFI 42 uses a colon prefix on identifiers (which by the way  
> is illegal in R5RS except for a lone colon).

Oops, it is illegal? I thought I checked before proposing the
:<type> syntax for generators in SRFI 42...

...ok, identifiers may start with a ':' according to R5RS:

  <identifier> -> <initial> <subsequent>^*
  <initial> -> <letter> | <special initial>
  <special initial> -> :
  <subsequent> -> <initial> | <digit>

You are probably mixing it up with <peculiar identifier>,
(+ - ...) which must not be followed by other stuff.

Which also means, btw, that the <keyword>: syntax *does*
conflict with R5RS identifiers.

Marc, am I missing something here?

Sebastian