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Re: Concern around use of eval

From: Stefan Monnier
Subject: Re: Concern around use of eval
Date: Thu, 19 Mar 2015 10:07:55 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.0.50 (gnu/linux)

> | (defvar lh/labels '("label1" "label2" "label3"))
> | 
> | (defmacro lh/gen-predicate (label)
> |   `(defun ,(intern (concat "lh/" label "-p")) ()
> |             (member ,label *lh/system-label-store*)))
> | 
> | (defun lh/define-predicates ()
> |   (dolist (label lh/labels)
> |     (eval `(lh/gen-predicate ,label))))
> | (lh/define-predicates)

    ; -*- lexical-binding:t -*-

    (defvar lh/labels '("label1" "label2" "label3"))
    (defun lh/gen-predicate (label)
      (defalias (intern (concat "lh/" label "-p"))
        (lambda () (member label *lh/system-label-store*))))
    (defun lh/define-predicates ()
      (mapc #'lh/gen-predicate lh/labels))


> Stylistically, is there a better way to do this or am I just being
> weird about (eval) and should just get over it?

You're not weird about `eval'.  It's kind of like self-modifying code:
there are cases where you *really* need it, but they're extremely rare
and every time you use it when it's not *really* indispensable,
kittens die.


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