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1 point by Adlai 5679 days ago | link | parent

'extend is great! However, I think it's more of a great library/patch, than something that should sit with the core functions. 'redef, on the other hand, is elegant, transparent ('extend is transparentially challenged...), and works well for quick hacks. 'extend seems to me to be more suited for setting in stone some behavior sketched out with 'redef (for example, the method-like behavior that you described in the original thread about 'extend http://arclanguage.org/item?id=8895)

The example you have of + on tables uses the algorithm that conses up a storm...



1 point by CatDancer 5678 days ago | link

One thing I like about 'extend is that I can run it several times while developing an extension without my older, buggy versions remaining on the call chain. Try actually hacking with this version of 'redef, it turns out to be really quite a pain!

  arc> (redef + args
         (apply (if (sll [isa _ 'table] args)
                     table+-better
                     orig)
           args))
oops, typo, try again

  arc> (redef + args
         (apply (if (all [isa _ 'table] args)
                     table+-better
                     orig)
           args))
oops, this 'redef is now calling the previous 'redef, I'm stuck!

On the other hand I don't think the explicit separation in 'extend between the test of whether to apply the extension from the implementation of the extension has turned out to be all that useful, so maybe some combination of the two would be better.

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1 point by Adlai 5678 days ago | link

Rudimentary hack to fix that:

  (= old-def (table))

  (mac redef (name args . body)
    `(let orig ,name
       (= (old-def ',name) orig)
       (= ,name (fn ,args ,@body))))

  (mac undef (name)
    `(= ,name (old-def ',name)))
I tried storing a list as each value in the table, and popping or pushing to/from the list in redef and undef, so that you could step backwards more than just one definition at a time. However, that made the entire thing much more unstable, because it turns out that 'push and 'pop rely on a bunch of functionality which breaks quite easily if you're messing with the internals.

So, this stripped down version is my little 'redef/'undef hack-pack.

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