33.  R^4RS Language Features not Implemented by Elk  

• Rational and complex numbers are not supported.
• Radix prefixes (#b, #o, #d, and #x) for real numbers are currently not implemented.
• The exponent markers s, f, d, and l are not implemented; the character # is not permitted in place of digits in numerical constants.
• char-ready is not implemented correctly (see above).
• transcript-on and transcript-off are not implemented.