A macro for writing defn-like macros?

[Mark]

I find the vast majority of the time I'm tempted to write a macro (yeah, yeah, I know the first rule of macro club), is to defn-like things.  Writing a defn-like macro to handle all the stuff defn does is pretty tough so I end up writing a barebones thing that doesn't support doc-string, doesn't support multiple arities, and doesn't support metadata.  I'm wondering, has anyone written a defdefnmacro macro?

[Ben Mabey]

On 9/3/13 10:01 AM, Mark wrote:

I find the vast majority of the time I'm tempted to write a macro (yeah, yeah, I know the first rule of macro club), is to defn-like things.  Writing a defn-like macro to handle all the stuff defn does is pretty tough so I end up writing a barebones thing that doesn't support doc-string, doesn't support multiple arities, and doesn't support metadata.  I'm wondering, has anyone written a defdefnmacro macro?

Clojure's tools.macros has a helper function for such macros called name-with-attributes:

https://github.com/clojure/tools.macro/blob/master/src/main/clojure/clojure/tools/macro.clj#L275-L298

HTH,
Ben

[Ben Wolfson]

I've got something that helps with this stuff: https://github.com/bwo/macroparser/blob/master/src/macroparser/functions.clj

On Tue, Sep 3, 2013 at 9:01 AM, Mark <markad...@gmail.com> wrote:

I find the vast majority of the time I'm tempted to write a macro (yeah, yeah, I know the first rule of macro club), is to defn-like things.  Writing a defn-like macro to handle all the stuff defn does is pretty tough so I end up writing a barebones thing that doesn't support doc-string, doesn't support multiple arities, and doesn't support metadata.  I'm wondering, has anyone written a defdefnmacro macro?

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Ben Wolfson
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[Ben Wolfson]

used, for example, here: https://github.com/bwo/monads/blob/master/src/monads/util.clj#L28-L43 and here: https://github.com/ReadyForZero/babbage/blob/1.1/src/babbage/graph.clj#L28-L79

[Alex Baranosky]

https://github.com/clojure/tools.macro/blob/master/src/main/clojure/clojure/tools/macro.clj#L275 ??

On Tue, Sep 3, 2013 at 9:01 AM, Mark <markad...@gmail.com> wrote:

I find the vast majority of the time I'm tempted to write a macro (yeah, yeah, I know the first rule of macro club), is to defn-like things.  Writing a defn-like macro to handle all the stuff defn does is pretty tough so I end up writing a barebones thing that doesn't support doc-string, doesn't support multiple arities, and doesn't support metadata.  I'm wondering, has anyone written a defdefnmacro macro?

--

[Jim - FooBar();]

I've been staring at this function for 20 minutes now (name-with-attributes)...I must be totally stupid but even though I 've understood what it does I can't figure out how to use it. Does anyone have an example usage? Let's suppose I want to define a DEFN macro that behaves exactly like defn...how would that go? I'm struggling to find examples of this on the web. I had previously resorted to my own solution but this certainly looks nicer...


thanks in advance :)

Jim

[Konrad Hinsen]

--On 3 septembre 2013 19:08:12 +0100 "Jim - FooBar();"

<jimpi...@gmail.com> wrote:

> understood what it does I can't figure out how to use it. Does anyone
> have an example usage? Let's suppose I want to define a DEFN macro that
> behaves exactly like defn...how would that go? I'm struggling to find

The general pattern is:

(defmacro defn [name & args]
(let [[name args] (name-with-attributes name args)]
... use name and args as if nothing has happened... )

For a real-life application see


https://github.com/clojure/algo.monads/blob/master/src/main/clojure/clojure/algo/monads.clj#L196

Konrad.

[Jim - FooBar();]

Yes! I eventually figured it out...thanks Konrad :)

Jim

[Phillip Lord]

For this, I just use defn. For example, this macro is like defn, but
also takes a function as the second argument. It composes the body with
function.

(defmacro defnwithfn [name function & body]
`(let [vr# (defn ~name ~@body)]
(alter-var-root
vr#
(fn [f#]
(fn ~name [& args#]
(apply ~function f# args#))))
vr#))

Basically, you let defn do the work, then fiddle with it after.

Phil

[Mark Addleman]

That's cool.  Thanks!

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