4 ms·

I wonder why tree shaking is so ineffective. Is that because any symbol could be accessed dynamically at runtime?

• jfoutz 10y ago
  eval is the root of all evil. String to symbol lets you introduce anything.
  • gkya 10y ago
    In lisp eval does not take a string as its input, but a form, i.e. a linked list, containing the program to execute. Maybe you confuse it with JavaScript or Python eval (or the like) where the function both reads in a string and runs the program it parsed from that string. There are diverse functions to convert a string to a symbol in different lisps.
    • jfoutz 10y ago
      Perhaps i'm rusty. in this case (funcall #'+ 1 2 3) or the more scheme-ish (apply '+ '(1 2 3)) i think the symbol plus gets evaluated to #<function+> and then is called with 1 2 3 - CL will do apply, of course, not sure about scheme and funcall. I'm totally willing to accept my mental model is wrong, i don't have an interpreter handy. So if that's true, you run into this problem: (funcall (string->symbol "+") 1 2 3) (apply (string->symbol "+") '(1 2 3)) maybe string->symbol does not introduce in to the function namespace, but i bet there's a way or a flag to do it. so anyway, at the end, you run into this problem: (funcall (string->symbol "any-random-function") 1 2 3) (apply (string->symbol "any-random-function") '(1 2 3)) this makes tree shaking hard. you could, of course, look for the handful of ways to bind symbols to functions, maybe do constant folding and include a minimal set if the compiler can prove what's actually needed. but in general i think tree shaking is hard when you can load things like that dynamically.
      • lispm 10y ago
        (funcall #'+ ...) does not do a symbol lookup and does not need to retrieve the function from a symbol in Common Lisp. (funcall '+ ...) would retrieve the function from the symbol. Treeshakers are generally used for application delivery in Lisp. When you do that, then one usually limits the amount of use of runtime dynamics. Typically you can tell the treeshaker what to remove or what to keep: the compiler, the symbol table, debugging info, etc etc. Allegro CL and LispWorks have extensive facilities for this. http://franz.com/support/documentation/10.0/doc/delivery.htm http://franz.com/support/documentation/10.0/doc/delivery.htm http://www.lispworks.com/documentation/lw70/DV/html/delivery.htm http://www.lispworks.com/documentation/lw70/DV/html/delivery...
        • kazinator 10y ago
          More briefly, in a half decent implementation, the + symbol is involved in the processing of (funcall #'+ ...) in the same ways and at the same times as it is involved in the plain call (+ ...).
• lispm 10y ago
  SBCL does treeshaking? I thought it just dumps the image.
  • throwaway91111 10y ago
    Well that would explain it. Any idea why they don't tree shake?
    • lispm 10y ago
      Because no one wrote one. There were some attempts but nothing which would work now. Delivering small applications does not seem to be a focus of SBCL users. https://www.snellman.net/blog/archive/2005-07-06.html https://www.snellman.net/blog/archive/2005-07-06.html There is also the possibility to compress the image. See :compression option when saving an image: http://www.sbcl.org/manual/#index-g_t_0040sbext_007bsave_002dlisp_002dand_002ddie_007d-7 http://www.sbcl.org/manual/#index-g_t_0040sbext_007bsave_002... Commercial Lisp implementations like LispWorks and Allegro CL have a treeshaker for delivery, but that's not too surprising, since these products are for developers of applications and the users pay for such features.