The following example shows an implementation of *eval-in* as a function.
There are a some *println* added to show the namespace where the code is
running at each point.
;;--------------------
(ns another-ns)
(defn X [w h]
{:w w :h h})
;;--------------------
(ns this-ns)
(defn eval-in [code ns]
(let [orig-ns *ns*]
(println *ns*) ; we are in this-ns
(in-ns (symbol ns))
(println *ns* (resolve *ns* 'X)) ; not anymore, now it's another-ns
(let [ret (eval (read-string code))]
(println *ns* (resolve *ns* 'X) ret) ; it's still another-ns but now
we have the return value
(in-ns (ns-name orig-ns))
(println *ns*) ; back to this-ns
ret)))
(def generator "(X 20 20)")
(println (eval-in generator "another-ns"))
(println (eval-in "(X 20 20)" "another-ns"))
;;--------------------
Cheers,
Juan
On Wednesday, December 19, 2012 4:22:58 AM UTC-3, nodename wrote:
>
> As an aside, I'm curious about whether this could have been implemented
> without a macro.
>
> -A
> On Dec 18, 2012 11:06 PM, "Alan Shaw" <node...@gmail.com <javascript:>>
> wrote:
>
>> Thanks very much Juan, that's some good study material for me.
>>
>> -A
>> On Dec 18, 2012 10:45 PM, "juan.facorro" <juan.f...@gmail.com<javascript:>>
>> wrote:
>>
>>> The macro sees it arguments as *symbols* and does not resolve to the
>>> corresponding *var* until evaluation, so the value for the local *code* var
>>> in the macro is actually the *symbol** generator.*
>>>
>>> The *eval-in* macro uses the *read-string* function to evaluate the
>>> code you provide, this function expects a string but it's getting the* *
>>> *symbol** generator* instead, since that's what the macro got as a
>>> first argument.
>>>
>>> Here's a modified version of the *eval-in* macro, that delays the
>>> evaluation of the call to *read-string*:
>>>
>>> (require '[clojure.pprint :as p])
>>>
>>> (defmacro eval-in
>>> [code ns]
>>> `(do
>>> (in-ns '~(symbol ns))
>>> (let [ret# (eval *(read-string ~code)*)] ; This line was changed
>>> (in-ns '~(ns-name *ns*))
>>> ret#)))
>>>
>>> (p/pprint (macroexpand '(eval-in generator "another-ns")))
>>>
>>> Here's the output:
>>>
>>> (do
>>> (clojure.core/in-ns 'another-ns)
>>> (clojure.core/let
>>> [ret__1879__auto__
>>> (clojure.core/eval *(clojure.core/read-string generator)*)] ; The
>>> unquoting of code resulted in the symbol generator
>>> (clojure.core/in-ns 'test-eval)
>>> ret__1879__auto__))
>>>
>>> If you want to use a var as an argument for the code, you could resolve
>>> the var before changing namespaces, delaying the read-string until the
>>> forms evaluation:
>>>
>>> (ns another-ns)
>>>
>>> (defn X [w h] [w h])
>>> ;---------------------------
>>> (ns this-ns
>>> (:require [clojure.pprint :as p]))
>>>
>>> (defmacro eval-in
>>> [code ns]
>>> `(let [code# ~code]
>>> (in-ns '~(symbol ns))
>>> (let [ret# (eval (read-string code#))]
>>> (in-ns '~(ns-name *ns*))
>>> ret#)))
>>>
>>> (def generator "(X 300 300)")
>>> (p/pprint (eval-in generator another-ns))
>>>
>>> Hope it helps,
>>>
>>> Juan
>>>
>>>
>>> On Wednesday, December 19, 2012 1:13:00 AM UTC-3, nodename wrote:
>>>>
>>>> From yesterday:
>>>>
>>>> (defmacro eval-in
>>>> "Eval a Clojure form in a different namespace and switch back to
>>>> current namespace.
>>>>
>>>> Args:
>>>> code - Clojure form as string
>>>> ns - Target namespace as string"
>>>> [code ns]
>>>> `(do
>>>> (in-ns '~(symbol ns))
>>>> (let [ret# (eval '~(read-string code))]
>>>> (in-ns '~(ns-name *ns*))
>>>> ret#)))
>>>>
>>>>
>>>>
>>>> user=> (def generator "(X 400 400)")
>>>> #'user/generator
>>>> user=> (def image (eval-in generator "clevolution.version.version0-**
>>>> 1-1"))
>>>> CompilerException java.lang.ClassCastException: clojure.lang.Symbol
>>>> cannot be cast to java.lang.String, compiling:(NO_SOURCE_PATH:1)
>>>>
>>>> user=> (def image (eval-in "(X 400 400)" "clevolution.version.version0-
>>>> **1-1"))
>>>> #'user/image
>>>>
>>>> So it's OK to pass the explicit string but not the symbol. What am I
>>>> not getting here?
>>>>
>>>> -A
>>>>
>>>>
>>>> On Tue, Dec 18, 2012 at 12:48 AM, Alan Shaw <node...@gmail.com> wrote:
>>>>
>>>>> Now I do, and the macro worked!
>>>>> I believe I have a problem using the macro from a function, but
>>>>> leaving that for tomorrow.
>>>>>
>>>>> Thanks BG!
>>>>>
>>>>> -A
>>>>>
>>>>>
>>>>>
>>>>> On Tue, Dec 18, 2012 at 12:19 AM, Baishampayan Ghose <b.g...@gmail.com
>>>>> > wrote:
>>>>>
>>>>>> Do you have target ns "clevolution.version.version0-**1-1" required?
>>>>>>
>>>>>> -BG
>>>>>>
>>>>>> On Tue, Dec 18, 2012 at 1:38 PM, Alan Shaw <node...@gmail.com> wrote:
>>>>>> > BG,
>>>>>> > The macro doesn't seem to do the trick. The function X is interned
>>>>>> in the
>>>>>> > target namespace, but:
>>>>>> >
>>>>>> > user=> (def image (eval-in "(X 400 400)"
>>>>>> > "clevolution.version.version0-**1-1"))
>>>>>> > CompilerException java.lang.RuntimeException: Unable to resolve
>>>>>> symbol: X in
>>>>>> > this context, compiling:(NO_SOURCE_PATH:1)
>>>>>> >
>>>>>> >
>>>>>> > On Mon, Dec 17, 2012 at 11:53 PM, Alan Shaw <node...@gmail.com>
>>>>>> wrote:
>>>>>> >>
>>>>>> >> Oh yes, the something.something is fixed so I can just prepend it,
>>>>>> thanks.
>>>>>> >> (Hadn't noticed your macro takes the ns as a string!)
>>>>>> >>
>>>>>> >> -A
>>>>>> >>
>>>>>> >>
>>>>>> >>
>>>>>> >> On Mon, Dec 17, 2012 at 11:47 PM, Baishampayan Ghose <
>>>>>> b.g...@gmail.com>
>>>>>> >> wrote:
>>>>>> >>>
>>>>>> >>> Alan,
>>>>>> >>>
>>>>>> >>> What you're asking for is to derive the ns "clojure.core" given
>>>>>> only
>>>>>> >>> "core". Not sure if that's possible.
>>>>>> >>>
>>>>>> >>> The namespace constitutes the whole dotted structure and not just
>>>>>> the
>>>>>> >>> last component, I am afraid.
>>>>>> >>>
>>>>>> >>> If the actual ns is something.something.version-0-**1-1, then
>>>>>> you need
>>>>>> >>> the string "something.something.version-**0-1-1" and not just
>>>>>> >>> "version-0-1-1" [unless of course you have some other way of
>>>>>> deriving
>>>>>> >>> it from info that's embedded in _your_ code or structure thereof].
>>>>>> >>>
>>>>>> >>>
>>>>>> >>> -BG
>>>>>> >>>
>>>>>> >>> On Tue, Dec 18, 2012 at 1:10 PM, Alan Shaw <node...@gmail.com>
>>>>>> wrote:
>>>>>> >>> > Thanks BG, I'm trying that.
>>>>>> >>> > But I don't think it addresses how to get from the string
>>>>>> >>> > "version-0-1-1" to
>>>>>> >>> > the namespace something.something.version-0-**1-1. How can I
>>>>>> do that?
>>>>>> >>> >
>>>>>> >>> > -A
>>>>>> >>> >
>>>>>> >>> >
>>>>>> >>> >
>>>>>> >>> > On Mon, Dec 17, 2012 at 11:26 PM, Baishampayan Ghose
>>>>>> >>> > <b.g...@gmail.com>
>>>>>> >>> > wrote:
>>>>>> >>> >>
>>>>>> >>> >> Alan,
>>>>>> >>> >>
>>>>>> >>> >> Something like this might work for you -
>>>>>> >>> >>
>>>>>> >>> >> (defmacro eval-in
>>>>>> >>> >> "Eval a Clojure form in a different namespace and switch
>>>>>> back to
>>>>>> >>> >> current namespace.
>>>>>> >>> >>
>>>>>> >>> >> Args:
>>>>>> >>> >> code - Clojure form as string
>>>>>> >>> >> ns - Target namespace as string"
>>>>>> >>> >> [code ns]
>>>>>> >>> >> `(do
>>>>>> >>> >> (in-ns '~(symbol ns))
>>>>>> >>> >> (let [ret# (eval '~(read-string code))]
>>>>>> >>> >> (in-ns '~(ns-name *ns*))
>>>>>> >>> >> ret#)))
>>>>>> >>> >>
>>>>>> >>> >> Warning - I haven't really tested this code.
>>>>>> >>> >>
>>>>>> >>> >> -BG
>>>>>> >>> >>
>>>>>> >>> >> On Tue, Dec 18, 2012 at 12:37 PM, Alan Shaw <node...@gmail.com
>>>>>> >
>>>>>> >>> >> wrote:
>>>>>> >>> >> > Thanks, Las!
>>>>>> >>> >> >
>>>>>> >>> >> > Ok say I have a file in which there is string such as
>>>>>> >>> >> >
>>>>>> >>> >> > "(- (atan (bw-noise 902 2 0.7604615575402431 400 400))
>>>>>> >>> >> > (read-image-from-file
>>>>>> >>> >> > \"images/Dawn_on_Callipygea.**png\"))"
>>>>>> >>> >> >
>>>>>> >>> >> > and another
>>>>>> >>> >> >
>>>>>> >>> >> > "version-0-0-1"
>>>>>> >>> >> >
>>>>>> >>> >> > and I have a namespace version-0-0-1 into which functions
>>>>>> named atan
>>>>>> >>> >> > etc.
>>>>>> >>> >> > are all :referred. I want to evaluate the expression in that
>>>>>> >>> >> > particular
>>>>>> >>> >> > context, and not remain there when I'm done.
>>>>>> >>> >> >
>>>>>> >>> >> > -A
>>>>>> >>> >> >
>>>>>> >>> >> >
>>>>>> >>> >> >
>>>>>> >>> >> > On Mon, Dec 17, 2012 at 11:00 PM, László Török <
>>>>>> ltor...@gmail.com>
>>>>>> >>> >> > wrote:
>>>>>> >>> >> >>
>>>>>> >>> >> >> ah, sorry, it's a bit early for me
>>>>>> >>> >> >>
>>>>>> >>> >> >> (in-ns (ns-name user-ns))
>>>>>> >>> >> >>
>>>>>> >>> >> >> if you could post a simple example for the second part of
>>>>>> your
>>>>>> >>> >> >> question
>>>>>> >>> >> >> I
>>>>>> >>> >> >> maybe able to help.
>>>>>> >>> >> >>
>>>>>> >>> >> >> Las
>>>>>> >>> >> >>
>>>>>> >>> >> >> Alan Shaw 2012. december 18., kedd napon a következőt írta:
>>>>>> >>> >> >>
>>>>>> >>> >> >>> Ah no, that puts me in a new user-ns namespace! Not what I
>>>>>> wanted!
>>>>>> >>> >> >>>
>>>>>> >>> >> >>>
>>>>>> >>> >> >>> On Mon, Dec 17, 2012 at 10:51 PM, László Török
>>>>>> >>> >> >>> <ltor...@gmail.com>
>>>>>> >>> >> >>> wrote:
>>>>>> >>> >> >>>>
>>>>>> >>> >> >>>> Try (in-ns 'user-ns)
>>>>>> >>> >> >>>>
>>>>>> >>> >> >>>> Las
>>>>>> >>> >> >>>>
>>>>>> >>> >> >>>> On Dec 18, 2012 7:50 AM, "Alan Shaw" <node...@gmail.com>
>>>>>> wrote:
>>>>>> >>> >> >>>>>
>>>>>> >>> >> >>>>> user=> *ns*
>>>>>> >>> >> >>>>> #<Namespace user>
>>>>>> >>> >> >>>>> user=> (def user-ns *ns*)
>>>>>> >>> >> >>>>> #'user/user-ns
>>>>>> >>> >> >>>>> user=> user-ns
>>>>>> >>> >> >>>>> #<Namespace user>
>>>>>> >>> >> >>>>> user=> (in-ns user-ns)
>>>>>> >>> >> >>>>> ClassCastException clojure.lang.Namespace cannot be cast
>>>>>> to
>>>>>> >>> >> >>>>> clojure.lang.Symbol clojure.lang.RT$1.invoke
>>>>>> (RT.java:226)
>>>>>> >>> >> >>>>>
>>>>>> >>> >> >>>>> It appears I'm not understanding how namespaces are
>>>>>> represented.
>>>>>> >>> >> >>>>>
>>>>>> >>> >> >>>>> Also, is it just wrong of me to want to remember a
>>>>>> namespace I
>>>>>> >>> >> >>>>> was
>>>>>> >>> >> >>>>> working in and try to go back to it later?
>>>>>> >>> >> >>>>>
>>>>>> >>> >> >>>>> The slightly larger context is: I'm saving an
>>>>>> s-expression with
>>>>>> >>> >> >>>>> unqualified names in it into a file as a string. Also
>>>>>> saving a
>>>>>> >>> >> >>>>> string
>>>>>> >>> >> >>>>> indicating the name of the environment in which that
>>>>>> string
>>>>>> >>> >> >>>>> should
>>>>>> >>> >> >>>>> be (read
>>>>>> >>> >> >>>>> and) eval'ed so that the names will resolve to the
>>>>>> appropriate
>>>>>> >>> >> >>>>> functions.
>>>>>> >>> >> >>>>> Advice on managing this would be appreciated.
>>>>>> >>> >> >>>>>
>>>>>> >>> >> >>>>> -Alan Shaw
>>>>>> >>> >> >>>>>
>>>>>> >>> >> >>>>> --
>>>>>> >>> >> >>>>> You received this message because you are subscribed to
>>>>>> the
>>>>>> >>> >> >>>>> Google
>>>>>> >>> >> >>>>> Groups "Clojure" group.
>>>>>> >>> >> >>>>> To post to this group, send email to
>>>>>> clo...@googlegroups.com
>>>>>> >>> >> >>>>> Note that posts from new members are moderated - please
>>>>>> be
>>>>>> >>> >> >>>>> patient
>>>>>> >>> >> >>>>> with
>>>>>> >>> >> >>>>> your first post.
>>>>>> >>> >> >>>>> To unsubscribe from this group, send email to
>>>>>> >>> >> >>>>> clojure+u...@**googlegroups.com
>>>>>> >>> >> >>>>> For more options, visit this group at
>>>>>> >>> >> >>>>> http://groups.google.com/**group/clojure?hl=en<http://groups.google.com/group/clojure?hl=en>
>>>>>> >>> >> >>>>
>>>>>> >>> >> >>>> --
>>>>>> >>> >> >>>> You received this message because you are subscribed to
>>>>>> the
>>>>>> >>> >> >>>> Google
>>>>>> >>> >> >>>> Groups "Clojure" group.
>>>>>> >>> >> >>>> To post to this group, send email to
>>>>>> clo...@googlegroups.com
>>>>>> >>> >> >>>> Note that posts from new members are moderated - please be
>>>>>> >>> >> >>>> patient
>>>>>> >>> >> >>>> with
>>>>>> >>> >> >>>> your first post.
>>>>>> >>> >> >>>> To unsubscribe from this group, send email to
>>>>>> >>> >> >>>> clojure+u...@**googlegroups.com
>>>>>> >>> >> >>>> For more options, visit this group at
>>>>>> >>> >> >>>> http://groups.google.com/**group/clojure?hl=en<http://groups.google.com/group/clojure?hl=en>
>>>>>> >>> >> >>>
>>>>>> >>> >> >>>
>>>>>> >>> >> >>> --
>>>>>> >>> >> >>> You received this message because you are subscribed to
>>>>>> the Google
>>>>>> >>> >> >>> Groups "Clojure" group.
>>>>>> >>> >> >>> To post to this group, send email to
>>>>>> clo...@googlegroups.com
>>>>>> >>> >> >>> Note that posts from new members are moderated - please be
>>>>>> patient
>>>>>> >>> >> >>> with
>>>>>> >>> >> >>> your first post.
>>>>>> >>> >> >>> To unsubscribe from this group, send email to
>>>>>> >>> >> >>> clojure+u...@**googlegroups.com
>>>>>> >>> >> >>> For more options, visit this group at
>>>>>> >>> >> >>> http://groups.google.com/**group/clojure?hl=en<http://groups.google.com/group/clojure?hl=en>
>>>>>> >>> >> >>
>>>>>> >>> >> >>
>>>>>> >>> >> >>
>>>>>> >>> >> >> --
>>>>>> >>> >> >> László Török
>>>>>> >>> >> >>
>>>>>> >>> >> >> --
>>>>>> >>> >> >> You received this message because you are subscribed to the
>>>>>> Google
>>>>>> >>> >> >> Groups "Clojure" group.
>>>>>> >>> >> >> To post to this group, send email to
>>>>>> clo...@googlegroups.com
>>>>>> >>> >> >> Note that posts from new members are moderated - please be
>>>>>> patient
>>>>>> >>> >> >> with
>>>>>> >>> >> >> your first post.
>>>>>> >>> >> >> To unsubscribe from this group, send email to
>>>>>> >>> >> >> clojure+u...@**googlegroups.com
>>>>>> >>> >> >> For more options, visit this group at
>>>>>> >>> >> >> http://groups.google.com/**group/clojure?hl=en<http://groups.google.com/group/clojure?hl=en>
>>>>>> >>> >> >
>>>>>> >>> >> >
>>>>>> >>> >> > --
>>>>>> >>> >> > You received this message because you are subscribed to the
>>>>>> Google
>>>>>> >>> >> > Groups "Clojure" group.
>>>>>> >>> >> > To post to this group, send email to clo...@googlegroups.com
>>>>>> >>> >> > Note that posts from new members are moderated - please be
>>>>>> patient
>>>>>> >>> >> > with
>>>>>> >>> >> > your
>>>>>> >>> >> > first post.
>>>>>> >>> >> > To unsubscribe from this group, send email to
>>>>>> >>> >> > clojure+u...@**googlegroups.com
>>>>>> >>> >> > For more options, visit this group at
>>>>>> >>> >> > http://groups.google.com/**group/clojure?hl=en<http://groups.google.com/group/clojure?hl=en>
>>>>>> >>> >>
>>>>>> >>> >>
>>>>>> >>> >>
>>>>>> >>> >> --
>>>>>> >>> >> Baishampayan Ghose
>>>>>> >>> >> b.ghose at gmail.com
>>>>>> >>> >>
>>>>>> >>> >> --
>>>>>> >>> >> You received this message because you are subscribed to the
>>>>>> Google
>>>>>> >>> >> Groups "Clojure" group.
>>>>>> >>> >> To post to this group, send email to clo...@googlegroups.com
>>>>>> >>> >> Note that posts from new members are moderated - please be
>>>>>> patient
>>>>>> >>> >> with
>>>>>> >>> >> your first post.
>>>>>> >>> >> To unsubscribe from this group, send email to
>>>>>> >>> >> clojure+u...@**googlegroups.com
>>>>>> >>> >> For more options, visit this group at
>>>>>> >>> >> http://groups.google.com/**group/clojure?hl=en<http://groups.google.com/group/clojure?hl=en>
>>>>>> >>> >
>>>>>> >>> >
>>>>>> >>> > --
>>>>>> >>> > You received this message because you are subscribed to the
>>>>>> Google
>>>>>> >>> > Groups "Clojure" group.
>>>>>> >>> > To post to this group, send email to clo...@googlegroups.com
>>>>>> >>> > Note that posts from new members are moderated - please be
>>>>>> patient with
>>>>>> >>> > your
>>>>>> >>> > first post.
>>>>>> >>> > To unsubscribe from this group, send email to
>>>>>> >>> > clojure+u...@**googlegroups.com
>>>>>> >>> > For more options, visit this group at
>>>>>> >>> > http://groups.google.com/**group/clojure?hl=en<http://groups.google.com/group/clojure?hl=en>
>>>>>> >>>
>>>>>> >>>
>>>>>> >>>
>>>>>> >>> --
>>>>>> >>> Baishampayan Ghose
>>>>>> >>> b.ghose at gmail.com
>>>>>> >>>
>>>>>> >>> --
>>>>>> >>> You received this message because you are subscribed to the Google
>>>>>> >>> Groups "Clojure" group.
>>>>>> >>> To post to this group, send email to clo...@googlegroups.com
>>>>>> >>> Note that posts from new members are moderated - please be
>>>>>> patient with
>>>>>> >>> your first post.
>>>>>> >>> To unsubscribe from this group, send email to
>>>>>> >>> clojure+u...@**googlegroups.com
>>>>>> >>> For more options, visit this group at
>>>>>> >>> http://groups.google.com/**group/clojure?hl=en<http://groups.google.com/group/clojure?hl=en>
>>>>>> >>
>>>>>> >>
>>>>>> >
>>>>>> > --
>>>>>> > You received this message because you are subscribed to the Google
>>>>>> > Groups "Clojure" group.
>>>>>> > To post to this group, send email to clo...@googlegroups.com
>>>>>> > Note that posts from new members are moderated - please be patient
>>>>>> with your
>>>>>> > first post.
>>>>>> > To unsubscribe from this group, send email to
>>>>>> > clojure+u...@**googlegroups.com
>>>>>> > For more options, visit this group at
>>>>>> > http://groups.google.com/**group/clojure?hl=en<http://groups.google.com/group/clojure?hl=en>
>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Baishampayan Ghose
>>>>>> b.ghose at gmail.com
>>>>>>
>>>>>> --
>>>>>> You received this message because you are subscribed to the Google
>>>>>> Groups "Clojure" group.
>>>>>> To post to this group, send email to clo...@googlegroups.com
>>>>>> Note that posts from new members are moderated - please be patient
>>>>>> with your first post.
>>>>>> To unsubscribe from this group, send email to
>>>>>> clojure+u...@**googlegroups.com
>>>>>> For more options, visit this group at
>>>>>> http://groups.google.com/**group/clojure?hl=en<http://groups.google.com/group/clojure?hl=en>
>>>>>>
>>>>>
>>>>>
>>>> --
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>>
>>
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