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1 point by evanrmurphy 2826 days ago | link | parent

Ahh defgeneric! I hadn't made the connection, thanks for pointing it out. :) Is this the writeup you'd recommend?

I think I had trouble digesting it a few months ago because it depended on so many utilities I was unfamiliar with: vtables, defmethod, pickles (and it compared with extend, which I didn't understand back then :-o ). Giving it another try...

2 points by akkartik 2826 days ago | link

It's in anarki so perhaps it'd be easier to just play with what the different defgenerics (iso, len, ..) there expand to.

vtables and pickles aren't utilities, just implementation details for defgeneric.

Basically vtables contains a hashtable for each generic function mapping a type to an implementation. "If len gets a string, do this. If it gets a table, do that." The body given to defgeneric sets up vtable entries for a few default types (cons, mainly :), and defmethod lets you add to vtables later.

If the generic function doesn't find an entry in vtables it falls back on searching the pickles table for a procedure to convert that type to cons, before retrying.

Let me know if this makes sense.

(names: I believe vtables comes from C++, and pickle is the python primitive for serialization)