> By the way, while playing with this problem, I ran into a moderately > painful issue. > > There is a reason that Smalltalk has both #printString (to get a > printable representation of an object) and #asString (to convert a > sequence to another kind of sequence with the same elements.) If I > *want* #printString, I know where to find it. The definition in my > Smalltalk no reads > > asString > "What should #($a $b $c) do? > - Blue Book, Inside Smalltalk, Apple Smalltalk-80: > there is no #asString. > - ANSI, VW, Dolphin, CSOM: > #asString is defined on characters and strings > (and things like file names and URIs that are sort of strings), > so expect an error report. > - VisualAge Smalltalk: > '($a $b $c)' > - Squeak and Pharo: > '#($a $b $c)' > - GNU Smalltalk, Smalltalk/X, and astc: > 'abc' > I don't intend any gratuitous incompatibility, but when there > is no consensus to be compatible with, one must pick something, > and this seems most useful. > " > ^String withAll: self
The asString looks wrong to me. I will report it as a bug. Now in Pharo we should really introduce display string > #($a $b $c) > > Does anyone here know WHY Squeak and Pharo do what they do here? > > On Wed, 6 May 2020 at 01:20, Richard O'Keefe <rao...@gmail.com> wrote: >> >> The irony is that the code I was responding to ISN'T obviously correct. >> Indeed, I found it rather puzzling. >> The problem specification says that the input string may contain digits >> AND SPACES. The original message includes this: >> >> Strings of length 1 or less are not valid. Spaces are allowed in the >> input, but they should be stripped before checking. All other >> non-digit characters are disallowed. >> >> Now it isn't clear what "disallowed" means. I took it to mean "may occur and >> should simply mean the input is rejected as invalid." Perhaps "may not >> occur" >> was the intention. So we shall not quibble about such characters. >> >> But I can't for the life of me figure out how Trygve's code checks for >> spaces. >> One reason this is an issue is that the behaviour of #digitValue is not >> consistent between systems. >> Character space digitValue >> does not exist in the ANSI standard >> answers -1 in many Smalltalks (which is a pain) >> answers a positive integer that can't be mistake for a digit in my >> Smalltalk >> raises an exception in some Smalltalks. >> >> This is a comment I now have in my Smalltalk library for #digitValue >> "This is in the Blue Book, but unspecified on non-digits. >> Squeak, Pharo, Dolphin, VW, VAST, and Apple Smalltalk-80 >> answer -1 for characters that are not digits (or ASCII letters), >> which is unfortunate but consistent with Inside Smalltalk >> which specifies this result for non-digits. >> ST/X and GST raise an exception which is worse. >> Digitalk ST/V documentation doesn't specify the result. >> This selector is *much* easier to use safely if it >> returns a 'large' (>= 36) value for non-digits." >> >> Let's compare three versions, the two I compared last time, >> and the "version A" code I discussed before, which to my mind >> is fairly readable. >> >> "Don't add slowness": 1 (normalised time) >> "Trygve's code": 6.5 >> "High level code": 30.6 (or 4.7 times slower than Trygve's) >> >> Here's the "High level code". >> ^(aString allSatisfy: [:each | each isSpace or: [each isDigit]]) and: [ >> |digitsReverse| >> digitsReverse := (aString select: [:each | each isDigit]) reverse. >> digitsReverse size > 1 and: [ >> |evens odds evenSum oddSum| >> odds := digitsReverse withIndexSelect: [:y :i | i odd]. >> evens := digitsReverse withIndexSelect: [:x :i | i even]. >> oddSum := odds detectSum: [:y | y digitValue]. >> evenSum := evens detectSum: [:x | >> #(0 2 4 6 8 1 3 5 7 9) at: x digitValue + 1]. >> (oddSum + evenSum) \\ 10 = 0]] >> >> This is the kind of code I was recommending that Roelof write. >> >> As a rough guide, by counting traversals (including ones inside existing >> methods), I'd expect the "high level" code to be at least 10 times slower >> than the "no added slowness" code. >> >> We are in vehement agreement that there is a time to write high level >> really obvious easily testable and debuggable code, and that's most >> of the time, especially with programming exercises. >> >> I hope that we are also in agreement that factors of 30 (or even 6) >> *can* be a serious problem. I mean, if I wanted something that slow, >> I'd use Ruby. >> >> I hope we are also agreed that (with the exception of investigations >> like this one) the time to hack on something to make it faster is AFTER >> you have profiled it and determined that you have a problem. >> >> But I respectfully suggest that there is a difference taking slowness OUT >> and simply not going out of your way to add slowness in the first place. >> >> I'd also like to remark that my preference for methods that traverse a >> sequence exactly once has more to do with Smalltalk protocols than >> with efficiency. If the only method I perform on an object is #do: >> the method will work just as well for readable streams as for >> collections. If the only method I perform on an object is #reverseDo: >> the method will work just as well for Read[Write]Streams as for >> SequenceReadableCollections, at least in my library. It's just like >> trying to write #mean so that it works for Durations as well as Numbers. >> >> Oh heck, I suppose I should point out that much of the overheads in >> this case could be eliminated by a Self-style compiler doing dynamic >> inlining + loop fusion. There's no reason *in principle*, given enough >> people, money, and time, that the differences couldn't be greatly >> reduced in Pharo. >> >> On Tue, 5 May 2020 at 21:50, Trygve Reenskaug <tryg...@ifi.uio.no> wrote: >>> >>> Richard, >>> >>> Thank you for looking at the code. It is comforting to learn that the code >>> has been executed for a large number of examples without breaking. The code >>> is not primarily written for execution but for being read and checked by >>> the human end user. It would be nice if we could also check that it gave >>> the right answers, but I don't know how to do that. >>> >>> The first question is: Can a human domain expert read the code and sign >>> their name for its correctness? >>> >>> >>> When this is achieved, a programming expert will transcribe the first code >>> to a professional quality program. This time, the second code should be >>> reviewed by an independent programmer who signs their name for its correct >>> transcription from the first version. >>> >>> --Trygve >>> >>> PS: In his 1991 Turing Award Lecture, Tony Hoare said: "There are two ways >>> of constructing a software design: One way is to make it so simple that >>> there are obviously no deficiencies and the other is to make it so >>> complicated that there are no obvious deficiencies. The first method is far >>> more difficult." >>> >>> --Trygve >>> >>> On tirsdag.05.05.2020 04:41, Richard O'Keefe wrote: >>> >>> As a coding experiment, I adapted Trygve Reenskoug's code to my >>> Smalltalk compiler, put in my code slightly tweaked, and benchmarked >>> them on randomly generated data. >>> >>> Result: a factor of 6.3. >>> >>> In Squeak it was a factor of ten. >>> >>> I had not, in all honesty, expected it to to be so high. >>> >>> On Tue, 5 May 2020 at 02:00, Trygve Reenskaug <tryg...@ifi.uio.no> wrote: >>> >>> A coding experiment. >>> Consider a Scrum development environment. Every programming team has an end >>> user as a member. >>> The team's task is to code a credit card validity check. >>> A first goal is that the user representative shall read the code and agree >>> that it is a correct rendering of their code checker: >>> >>> luhnTest: trialNumber >>> | s1 odd s2 even charValue reverse | >>> ----------------------------------------------- >>> " Luhn test according to Rosetta" >>> "Reverse the order of the digits in the number." >>> reverse := trialNumber reversed. >>> "Take the first, third, ... and every other odd digit in the reversed >>> digits and sum them to form the partial sum s1" >>> s1 := 0. >>> odd := true. >>> reverse do: >>> [:char | >>> odd >>> ifTrue: [ >>> s1 := s1 + char digitValue. >>> ]. >>> odd := odd not >>> ]. >>> "Taking the second, fourth ... and every other even digit in the reversed >>> digits: >>> Multiply each digit by two and sum the digits if the answer is greater than >>> nine to form partial sums for the even digits" >>> "The subtracting 9 gives the same answer. " >>> "Sum the partial sums of the even digits to form s2" >>> s2 := 0. >>> even := false. >>> reverse do: >>> [:char | >>> even >>> ifTrue: [ >>> charValue := char digitValue * 2. >>> charValue > 9 ifTrue: [charValue := charValue - 9]. >>> s2 := s2 + charValue >>> ]. >>> even := even not >>> ]. >>> "If s1 + s2 ends in zero then the original number is in the form of a valid >>> credit card number as verified by the Luhn test." >>> ^(s1 + s2) asString last = $0 >>> --------------------------------- >>> Once this step is completed, the next step will be to make the code right >>> without altering the algorithm (refactoring). The result should be readable >>> and follow the team's conventions. >>> >>> >>> P.S. code attached. >>> >>> >>> -- >>> >>> The essence of object orientation is that objects collaborate to achieve a >>> goal. >>> Trygve Reenskaug mailto: tryg...@ifi.uio.no >>> Morgedalsvn. 5A http://folk.uio.no/trygver/ >>> N-0378 Oslo http://fullOO.info >>> Norway Tel: (+47) 468 58 625 > -------------------------------------------- Stéphane Ducasse http://stephane.ducasse.free.fr / http://www.pharo.org 03 59 35 87 52 Assistant: Julie Jonas FAX 03 59 57 78 50 TEL 03 59 35 86 16 S. Ducasse - Inria 40, avenue Halley, Parc Scientifique de la Haute Borne, Bât.A, Park Plaza Villeneuve d'Ascq 59650 France
