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----- Forwarded message from oleg@xxxxxxxxx ----- Envelope-to: scgmille@localhost Delivery-date: Fri, 01 Aug 2003 13:43:19 -0500 To: scgmille@xxxxxxxxxxxxxxxxxx Subject: Re: [oleg@xxxxxxxxx: Minor quibbles on the latest draft] Reply-To: oleg@xxxxxxxxx From: oleg@xxxxxxxxx Hello! I'm replying to you although my comments are public. I'm afraid that my mail to SRFI-44 would bounce, therefore, I don't explicitly send to the list. Please feel free to forward or publicly reply on the list. [Re: advanced module system] > The problem with this approach is that it doesn't let you use two > collections of different types by the same Scheme function. For > example: > > (define (myfunc a) > (set-contains? a 3)) > > (myfunc (foo-set 1 2 3)) > (myfunc (bar-set 4 5 6)) I'm afraid I failed to emphasize that I do not argue against OOP, typeclasses or a similar facility. If a function is polymorphic with respect to collections, as myfunc is, generally a dynamic dispatch is required. This is true in general of polymorphic functions or constrained polymorphic functions -- e.g., like '+' in Scheme. The addition function should, at run-time, check if its arguments are fixnum, bignum, rational, inexact, complex, etc -- and dispatch to the appropriate addition function for specific sorts of numbers. However, a compiler may often infer that a particular '+' in the code will be applied only to exact integer arguments. The compiler can therefore compile the appropriate specialized function there. This is, in essence, a common technique of monomorphizing polymorphic functions (which is similar to C++ template expansion). OCaml and Bigloo do that often. Type declarations -- or in the case of Scheme module declarations -- greatly help the compiler to make monomorphizing decisions. Users can do monomorphizing by hand or given the compiler specific instructions: e.g., in Gambit (let () (##declare (fixnum)) (+ 1 2))) SRFI-44 is not a SRFI about modules, generic functions or OOP systems. Still, the 'issues' section of SRFI-44 does mention OOP and generic functions and dynamic dispatch -- but does not say anything about module systems and static dispatch. I thought that's odd. The latter, although not general, do turn out useful in many circumstances. > > Edison says: insert [our add] keeps the new element in case of > > duplicates, but insertSeq [our add-all] keeps an unspecified element. > In the case of bags, its perfectly valid to keep all the values. Did > you mean sets? Yes, of course. I pasted the wrong lines... >> For ordered collections, Edison defines procedures to view, insert or BTW, view functions are quite nifty: they are deconstructors. So we could write (let-values (((max-val rest) (ordered-coll-remove-max coll))) ...) The syntax even reminiscent of pattern-matching (aka Prolog's [Head|T]). It also permits pure-functional removal functions. Cheers, Oleg ----- End forwarded message ----- --
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