Keywords look like :foo, foo:, or #:foo, depending on the Scheme implementation:

• Gauche (and Common Lisp) support :foo.

• Gambit, Kawa (and DSSSL, SRFI 88) support foo:.

• Bigloo, STklos supports both foo: and :foo and treats them as the same (in the sense of eqv?).

• Scheme 7 supports both foo: and :foo and treats them as distinct (in the sense of eqv?).

• PLT supports #:foo.

• Chicken, Guile supports #:foo always, and also allows either foo: or :foo depending on the setting of a parameter or a startup option.

• MIT, Scheme48/scsh, SISC, Chez, SCM, Ikarus, Larceny, Mosh, Scheme 9, SSCM, SXM, VSCM, Chibi don't support any of them.

If we adopt the :foo style, Gauche, Bigloo, Scheme 7, STklos will work out of the box, and Chicken and Guile will support it with an option.

If we adopt the foo: style, Gambit, Chicken, Kawa, STklos, Bigloo, Scheme 7 will work out of the box, and Guile will support it with an option.

If we adopt the #:foo style, PLT, Chicken, Bigloo, Guile, Scheme 7 will work out of the box.