On 14 June 2010 16:27, Eli Barzilay <e...@barzilay.org> wrote: > On Jun 14, Brian Harvey wrote: > > language to support teams of 500 lousy programmers. > > What I understood from David is that when he uses `map' in his code, > he will never pass it a function that is not his too.
No. I simply never expose an encapsulated list structure to potentially malicious code. That is not the same thing as your understanding. I often provide type-specific map combinators *entirely* so that my encapsulations are not violated. Such is the big win of using a HOmF language like Scheme. If a user of one of my libraries wants to make their own list of my objects and then clobber its structure that's entirely her own business, but I don't provide access to *my* lists through *my* APIs. Seems that I need to repeat this a fifth time: > No, you don't. You have advocated a position which actually *removes* the ability to mutate one of the two basic aggregate types in Scheme. This seems rather arbitrary, and wrong-headed (due to knock-on effects) in light of things like breaking mutable a-lists. Scheme is a language which allows free mutation of bindings and primitive objects. Immutable pairs is a big step on a slippery slope to a very different language. currently (RnRS) Scheme is guessing wrong in >99% of the > cases, and it makes it extremely hard for me to correct it. > This is FUD. The occurrence of the class of bugs for which you have highlighted the potential is *far* (orders of magnitude) lower than this. You have a point, and it is a real problem from a provability standpoint, but practically it just doesn't happen that often. The whole point of using a map combinator is so that you can abstract away from aggregate structure: anyone who is mutating the aggregate structure which is being operated on by the combinator has fundamentally *missed the point* and should be hung, drawn, and quartered (or at least made to fix the damn bug himself). david -- GPG Public key at http://cyber-rush.org/drr/gpg-public-key.txt
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