I was playing with code generation outside macro being inspired by corrected version of nif

https://letoverlambda.com/index.cl/guest/chap3.html#sec_5

When I replace the usual gensym with my interned-gensym I can skip the eval and have more noob friendly version of the code that I can easily copy to REPL for further experiments with macro code creation. 

When it’s done, will I be able to replace with defmacro?

Why the usual gensym in macro is not interned?

Besides the eval is evil, what are other pitfalls of writing code this way?

(defun interned-gensym ()  
  "More suitable variant of gensym for macro experiments"  
  ;; file:~/Programming/sbcl/src/code/symbol.lisp::593  
  (values (intern (format nil "Z~A"
  (let ((old *gensym-counter*))
    (setq *gensym-counter* (1+ old))
    old)))))

​

;;; nif

(eval (apply (lambda (expr pos zero neg)
  (let ((gexpr (interned-gensym)))
    `(let ((,gexpr ,expr))
    (cond 
      ((plusp ,gexpr) ,pos)
      ((zerop ,gexpr) ,zero)
      (T ,neg)))))
    ;; args for the lambda
    ((- 5 2) :positive :zero :negative)))

​

  • ruby_objectOPBEnglish
    1·
    10 months ago

    I could ensure I had no name clashes.

    However, my experiments have led me to understand double quoting. Seeing how level 1 quoting becomes unquoted and level 2 quoting becomes 1 one quoting and how once-only uses temporary variables gave me interesting insights. so while I will never use it in production, it was a very good experiment.