On 18.03.2009, at 19:03, Konrad Hinsen wrote:
> Why is user// an invalid token, whereas clojure.core// works
> perfectly well?
I found out in the meantime that clojure.core// is indeed handled as
a special case by the reader (line 276 in LispReader.java), but that
still doesn't answer the question "why". It is clear that the
unqualified part of a symbol can contain a slash only at the
beginning, as otherwise it could be taken for a qualified symbol. But
I don't see a problem with any of the following:
/ (unqualified /)
// (unqualified //)
user// (/ in namespace user)
/foo (unqualified /foo)
user//foo (/foo in namespace user)
But the reader allows only / and clojure.core// as special cases. Is
this just a limitation of the current implementation, or is there a
more fundamental reason?
A workaround I found is to create the symbol on the fly with a macro:
(defmacro qsym
[ns sym]
(symbol (str ns) (str sym)))
That makes it possible to refer to user// as (qsym user /), except
where the symbol would be an argument to another macro, in which case
there seems to be no way around defining a specialized version of
that macro, e.g.
(defmacro defmethod*
[ns name & args]
(let [qsym (symbol (str ns) (str name))]
(prn qsym)
`(defmethod ~qsym ~...@args)))
Konrad.
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