There's nothing specific to fold-right here. It's a general property that when we specify functions using algorithms like this, the algorithms are not designed to be efficient. And in turn, that's a property of specifications in general, not just this one. It's the way standards work.
Michael Kay Saxonica > On 12 Jan 2017, at 17:21, W.S. Hager <wsha...@gmail.com> wrote: > > Better still, remove fold-right entirely, since laziness isn't part of the > spec (specifically infinite lists). > > 2017-01-12 18:10 GMT+01:00 W.S. Hager <wsha...@gmail.com > <mailto:wsha...@gmail.com>>: > Can we please agree to add a footnote to the fold-right example that says > something along the lines of "this example algorithm may be optimized using > lazy evaluation in the interpreter"? I don't see how that is biasing the spec > toward a specific implementation... > > 2017-01-12 17:27 GMT+01:00 Michael Kay <m...@saxonica.com > <mailto:m...@saxonica.com>>: > > > > Agreed, but that wasn't my point. You may have the opinion that it wasn't > > important, but I'm curious to know where anything tangible on laziness is > > mentioned. > > It isn't - deliberately. We leave "quality of implementation" issues entirely > to the implementor. There are many implementation techniques available, > including ones that may not have been invented yet, and there are different > trade-offs between time and memory, and the spec quite deliberately doesn't > get involved in such matters. The spec tells you what result to expect, it > doesn't tell you when to expect it. > > Michael Kay > Saxonica > > > > As you say, not having any won't be very efficient, so you may as well be > > explicit about it, right? I don't really understand why it's preferable to > > have a syntax without an implementation, and I simply pointed out that in > > the case of the fold-right example that becomes slightly odd... > > > > > -- > W.S. Hager > Lagua Web Solutions > http://lagua.nl <http://lagua.nl/> > > > > -- > W.S. Hager > Lagua Web Solutions > http://lagua.nl <http://lagua.nl/>
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