[elephant-devel] A thorny problem....

[James Anderson]

hello;
  -----Original Message-----
  From: elephant-devel-bounces at common-lisp.net [mailto:elephant-devel-bounces at common-lisp.net]On Behalf Of Robert L. Read
  Sent: Friday, February 17, 2006 16.17
  To: Elephant-devel mailing list
  Subject: [elephant-devel] A thorny problem....


  I think I've a identified a serious problem relating to the
  the dependencies on various modules that I offer up
  for you comment.
   

  i have a naive know ledge  of elephant, but would be surprised that this is a problem.
  one writes a macro which targets a generic function.

  a macro does several useful things.
  1. it preforms syntactic rewriting
  2. it delays evaluation.
  3. if it is to be useful, this king of macro provides a standard interface to varying implementations.

  when i skim over the definitions which i find in utils.lisp and berkeley.lisp, i observe that thay do lots of 1, none of 2 and half of three, and that it appears that their siginficance to a bit of application code depends on the active package.

  in order to avoid what you describe as a thorny problem, you would need to
  - have one macro only. not different ones with analogous names in different packages.
  - have that macro always take the same syntax (which those seem, mostly, to do)
  - prepare all arguments to pass to an implementation-specific function
  - capture the body in a closure
  - invoke the implementation-specific function with a specializing argument, the closure, and the keyword arguments.

  the implementation-specific function is generic, with a method defined by each backend.

  the approach is good parcive in general for macros - means you don't need to recompile code if the implementation changes, but is essential to implement and use modular back.ends.

  ...
   
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