Evaluating with a lexical environment

[Spiros Bousbouras]

On Thu, 11 Jul 2019 21:39:34 +0200  Daniel Kochmański wrote:
>  > Looking in the ECL source I saw a  si::eval-with-env  function in file
>  > ecl-16.1.3/src/c/compiler.d .If you do
>  >
>  >> (find-symbol "EVAL-WITH-ENV" "SYSTEM")
>  > SI:EVAL-WITH-ENV
>  > :EXTERNAL
>  >
>  > which suggests that the function is not just for internal use. But 
>  > scanning the documentation , I didn't see it mentioned.
> 
> symbols in package system are part of ecl internals (this is 
> documented), they are not part of the api. Only symbols reexported to 
> ext are somewhat stable.

Ok , this confused me originally because I thought that 
"EXT" , "SYS" , "SYSTEM" were all nicknames for package "SI" .But it turns
out that this was true in an older version and now "EXT" is a separate package.

>  > I tried
>  >
>  > (defmacro env-eval (form &environment env)
>  >      `(ext:eval-with-env ,form (quote ,env)))
>  > ENV-EVAL
>  >> (let ((v 12)) (env-eval '(print v)))
>  > The variable V is unbound.
>  > Broken at EVAL.No restarts available.
>  > Broken at EVAL.
>  >
>  >
>  > So is there a way to achieve this ?
> 
> eval-with-evn accepts the lexical environment while environment put 
> there by defmacro is something else. You may use a hack, but I do not 
> guarantee it will work in all scenarios:
> 
> CL-USER> (defmacro eval-with-lexenv-ala-clisp (form)
>             `(let ((lexenv (nth-value 1 (function-lambda-expression 
> (lambda ())))))
>                (si:eval-with-env ,form lexenv)))
> EVAL-WITH-LEXENV-ALA-CLISP
> CL-USER> (let ((v 42))
>             (eval-with-lexenv-ala-clisp '(print v)))
> 
> 42
> 42

Thanks , this looks promising.

> Most notably this *won't* work in normally compiled code.

This won't be a problem.