Here are some things I've run across in Clojure that seem asymmetric to me
-- I looked through Jira for issues related to these, but I didn't find any
(of course, I might have just missed them). Some of these might be valid
enhancements that would make sense to add, some of them might be a case of
me having a bad mental model and wanting the wrong thing from the
language. I'm hoping to get some feedback to help me determine which is
which, and then I'll write some patches for the ideas that are good ones.
I've tried to avoid making any statements about the world (e.g. x is y),
these are all just statements about my personal experience (e.g. x seems
like y to me).
1.
user=> (keyword 'foo)
:foo
user=> (keyword "foo")
:foo
user=> (keyword :foo)
:foo
user=> (symbol "foo")
foo
user=> (symbol 'foo)
foo
user=> (symbol :foo)
ClassCastException clojure.lang.Keyword cannot be cast to java.lang.String
clojure.core/symbol (core.clj:522)
I've never wanted to create a symbol from a keyword, but this seems
asymmetrical to me.
2.
user=> (name 'user)
"user"
user=> (name :user)
"user"
user=> (name "user")
"user"
user=> (name *ns*)
ClassCastException clojure.lang.Namespace cannot be cast to
clojure.lang.Named clojure.core/name
(core.clj:1488)
I think of namespaces as being a thing that has a name, so I would expect
to be able to call name on them. I always do this first, and then it blows
up, and then I remember ns-name, but that returns a symbol, not a string
(which I also always forget), so then I finally have to pipe that through
name or str, which ends up seeming messier than it should to me.
user=> (name (ns-name *ns*))
"user"
One solution to that would be name namespaces a clojure.lang.Named, where
they return their own name -- which seems reasonable to me. But that would
lead us to this next case, below.
3.
user=> (namespace 'foo)
nil
user=> (namespace 'user/foo)
"user"
user=> (namespace :foo)
nil
user=> (namespace ::foo)
"user"
user=> (namespace *ns*)
ClassCastException clojure.lang.Namespace cannot be cast to
clojure.lang.Named clojure.core/namespace (core.clj:1496)
If we make Namespaces a clojure.lang.Named, then they'll also need to have
an implementation of getNamespace. I suppose we could return the
namespace's name, but does that imply that a namespace is in itself? That
seems wrong to me. Another option would be to return nil, which indicates
that a namespace is not in a namespace, which is true, but possibly
confusing. A third possibility would be to split Named into Named (has a
name) and Namespaced (has a namespace), and then we don't have this issue
at all -- we'd be free to say that namespaces are Named, but not
Namespaced.
4.
user=> (symbol "bar")
bar
user=> (symbol 'bar)
bar
user=> (symbol "foo" "bar")
foo/bar
user=> (symbol "foo" 'bar)
ClassCastException clojure.lang.Symbol cannot be cast to java.lang.String
clojure.core/symbol
(core.clj:523)
user=> (symbol 'foo 'bar)
ClassCastException clojure.lang.Symbol cannot be cast to java.lang.String
clojure.core/symbol
(core.clj:523)
user=> (symbol *ns*
'bar)
ClassCastException clojure.lang.Namespace cannot be cast to
java.lang.String clojure.core/symbol
(core.clj:523)
user=> (symbol *ns* "bar")
ClassCastException clojure.lang.Namespace cannot be cast to
java.lang.String clojure.core/symbol
(core.clj:523)
I always forget that symbol allows a string or a symbol for first argument,
but that when you have two arguments, they must both be strings. It's
another "d'oh!" thing for me that I find myself correcting a lot. I'd also
like to be able to construct a symbol with a namespace object directly, not
just the string that represents the namespace's name.
Anyway, what do you think? If there are any smart ideas here, I'd be happy
to create a jira ticket and attach a patch with tests.
Joe
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