This is pure gold - your answers! Thanks a lot. So the take outs and key
ideas for me are:
- The syntax quote '`', unquote '~' and I expect also the unquote splicing
'~@' can be nested.
- A global var doesn't need to be created by the `def` (in macro). Use the
`intern` function directly (and be aware of possible lazy evaluation).
- There's more to `macroexpand` than just the debugging. Think out of the
box!*
At the first glance I like the "use `intern`" idea at most and I'll give it
a try it the following form:
(defn def-stuff [x] (intern *ns* (symbol x) x))
(map def-stuff [...])
This way, I naively hope, I can reason about it the functional-programming
way:
Just create a function and map it over something. No code generation or
expansion trickery involved.
Again, thank you very much, I consider adding your examples to
https://clojuredocs.org/clojure.core/def
Bost
*as always :)
Le lun. 5 oct. 2020 à 13:02, Jeremy Heiler <jeremyhei...@gmail.com> a
écrit :
> Do you know about macroexpand?
>
> user=> (defmacro m1 [v] `(def (symbol ~v)))
> #'user/m1
> First argument to def must be a Symbol
> user=> (macroexpand '(m1 "foo"))
> (def (clojure.core/symbol "foo"))
> user=> (defmacro m2 [v] `(def ~(symbol v)))
> #'user/m2
> user=> (macroexpand '(m2 "foo"))
> (def foo)
>
> The trick here is that you need to convert v into a symbol when the macro
> is expanded, not at runtime.
>
> On Oct 2, 2020 at 3:37:52 PM, Rostislav Svoboda <
> rostislav.svob...@gmail.com> wrote:
>
>> I have a problem with `def` in macros. I'd like to create a bunch of
>> following definitions:
>>
>> (def foo "FOO")
>> (def bar "BAR")
>> (def baz "BAZ")
>>
>> So I wrote a macro:
>>
>> user=> (defmacro def-stuff [v] `(def (symbol ~v)
>> (clojure.string/upper-case ~v)))
>> #'user/def-stuff
>>
>> And I'd like to do map this macro over a vector of strings:
>>
>> user=> (map (fn [n] (def-stuff n)) ["foo" "bar" "baz"])
>> Syntax error compiling def at (REPL:1:14).
>> First argument to def must be a Symbol
>>
>> A little check indicates that everything should be fine:
>> user=> (symbol? (symbol "foo"))
>> true
>>
>> but it is not:
>> user=> (def (symbol "foo") "FOO")
>> Syntax error compiling def at (REPL:1:1).
>> First argument to def must be a Symbol
>>
>> ???
>> Interestingly enough:
>>
>> user=> (defmacro def-stuff [v] `(def v (clojure.string/upper-case ~v)))
>> #'user/def-stuff
>> user=> (map (fn [n] (def-stuff n)) ["foo" "bar" "baz"])
>> (#'user/v #'user/v #'user/v)
>>
>> Strangely enough a `v` gets (re)defined.
>>
>> To me it looks like the lexical-binding of macro-parameters is ignored if
>> there's a `(def <macro-param> ...)` inside this macro.
>>
>> Can anybody explain what's going on here please? Thanks.
>>
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