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Taylor R. Campbell wrote:
I'm missing one part of the rationale: Why do we need a separate data
type? Even in Common Lisp, keywords are symbols.
Common Lisp does have compound symbols, where a symbol comprises a
package and a package-local name. But while the CL keyword ":foo"
is a symbol, it is different from the symbol "foo" because it is
in a different package.
A plausible solution is to introduce two-level names, as in CL.
That has a number of uses. For example they could model XML's
two-level names. However, I wouldn't want Common Lisp's rather
complex package semantics. The problem is CL uses packages for
module visibility/import/export in an awkward way.
What we need are two predicates:
1: (general-symbol? x)
2: (simple-symbol? x) - which is true iff (general-symbol? x) and
x is in the default unnamed package.
Standard R5RS symbols satisfy simple-symbol?. Keywords, and the
special forms like #!optional satisfy general-symbol? but not
The "legacy predicate" symbol? should be equivalent to one of
general-symbol? or simple-symbol? but I'm not sure which. A
factor is an implementation may want to provide keywords without
full two-level symbols.
- From: "Taylor R. Campbell" <firstname.lastname@example.org>