On Mon, Dec 8, 2008 at 5:35 PM, Chouser <[EMAIL PROTECTED]> wrote:
>
> On Mon, Dec 8, 2008 at 3:40 PM, J. McConnell <[EMAIL PROTECTED]> wrote:
> >
> This is a breaking change for some (granted rather unsual) cases:
>
> (defmulti foo {:a 1 :b 2})
> (defmethod foo 1 [_] "got a1")
> (defmethod foo 2 [_] "got b2")
Or, worse yet:
(defmulti foo {:a {:b "B"}} {:c "C"})
Which would become ambiguous after this patch. Good catch, Chouser.
> I'm not offering an opinion here on whether or not it's a good patch,
> just wanted to point out it changes currently defined behavior.
Thanks for pointing that out. I did this mostly as a learning
experience, because it seemed like something that would be useful.
However, it's not something I have a need for at the moment, so I've
mostly gotten out of it what I was looking for :)
Before giving up on it, one approach that might work for now would be
to allow a doc-string, but not the attr-map. Since a string isn't a
valid parameter for the dispatch function, there would be no
possibility for ambiguity and I believe it is completely backwards
compatible. I've attached a patch that implements this. Sample usage:
1:7 user=> (defmulti #^{:arglists '([n])} fib "docs for fib" int)
#'user/fib
1:8 user=> (doc fib)
-------------------------
user/fib
([n])
docs for fib
nil
Thoughts welcome. I'll be happy to implement any suggested changes.
If, on the other hand, there is no further interest in this, I'll let
it go since I don't have a need for it at the moment, anyhow. However,
it does seem like it would be nice if defmulti had similar doc support
to defn and defmacro.
Regards,
- J.
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Index: src/clj/clojure/core.clj
===================================================================
--- src/clj/clojure/core.clj (revision 1147)
+++ src/clj/clojure/core.clj (working copy)
@@ -991,11 +991,19 @@
default-dispatch-val is supplied it becomes the default dispatch
value of the multimethod, otherwise the default dispatch value
is :default."
- ([name dispatch-fn] `(defmulti ~name ~dispatch-fn :default))
- ([name dispatch-fn default-val]
- `(def ~(with-meta name (assoc ^name :tag 'clojure.lang.MultiFn))
- (new clojure.lang.MultiFn ~dispatch-fn ~default-val))))
+ ([name & fdecl]
+ (let [docs (if (string? (first fdecl)) {:doc (first fdecl)})
+ dispatch-fn (if docs (second fdecl) (first fdecl))
+ default-val (or (if docs (second (rest fdecl)) (second fdecl))
+ :default)]
+ `(def ~(with-meta name (conj (assoc ^name :tag 'clojure.lang.MultiFn) docs))
+ (new clojure.lang.MultiFn ~dispatch-fn ~default-val)))))
+(.setMeta (var defmulti)
+ (conj (meta (var defmulti))
+ {:arglists '([name doc-string? dispatch-fn]
+ [name doc-string? dispatch-fn default-val])}))
+
(defmacro defmethod
"Creates and installs a new method of multimethod associated with dispatch-value. "
[multifn dispatch-val & fn-tail]
