On Fri, Jun 3, 2011 at 10:36 AM, nil <ache...@gmail.com> wrote:
>> The problem here is that macros run at compile time, but let bindings
>> exist at run time.
>>
>> If you need the name to be determined at run time you will need to use eval.
>
> Where do I use eval? I tried looking at the argument to see if it was
> called with a string literal vs a symbol, but can't eval a local:
>
> (defmacro foo [x]
> (let [name-as-string# (if (symbol? x) (eval x) x)
> name-as-symbol# (symbol name-as-string#)]
> `(defn ~name-as-symbol# [] ())))
>
> (let [eff "gee"] (foo eff))
You'd need to use eval *instead* of defmacro in that case:
=> (let [eff "gee"]
(eval `(defn ~(symbol (str "foo-" eff)) [] (println "Hello, world!"))))
#'user/foo-gee
=> (foo-gee)
Hello, world!
nil
=>
But there's probably a *much* better way to do whatever you're trying
to do that doesn't involve using eval.
>> If you don't need the name at run time, why are you using (let [eff
>> "gee"] (foo eff)) and not simply (foo gee)?
>
> I'm using let because I'd like to have the name at run time. I'm
> defining families of functions to manipulate types of UI elements by
> saying (type page-name field-name locator). Without knowing a solution
> to my problem, I'm stuck saying the following in order to generate a
> bunch of functions to use later in my program...
>
> (txt "registration" "username" "id=Username")
> (txt "registration" "password" "id=Password")
> (tog "registration" "terms" "id=AcceptTerms")
> (nav "registration" "submit" "//html/body/div/form/div/input" "/
> SignedIn")
>
> ... Instead of this:
>
> (let [page "registration"]
> (txt page "username" "id=Username")
> (txt page "password" "id=Password")
> (tog page "terms" "id=AcceptTerms")
> (nav page "submit" "//html/body/div/form/div/input" "/SignedIn"))
That should work if txt, tog, and nav are normal functions, and could
work if they're macros depending on how they're written, but I take it
they're macros and it doesn't work.
How about:
(doto "registration"
(txt "username" "id=Username")
(txt "password" "id=Password")
(tog "terms" "id=AcceptTerms")
(nav "submit" "//html/body/div/form/div/input" "/SignedIn"))
It's not exactly what the doto macro was intended for, but it *should* work.
--
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Master: Your father's Lisp REPL. This is the language of a true
hacker. Not as clumsy or random as C++; a language for a more
civilized age.
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