mentor question 4
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It's a good solution. On Sat, May 2, 2020, 00:52 Roelof Wobben via Pharo-users <[hidden email]> wrote: Op 1-5-2020 om 08:35 schreef Roelof Wobben: |
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In reply to this post by Pharo Smalltalk Users mailing list
On Sat, 2 May 2020 at 15:52, Roelof Wobben via Pharo-users <[hidden email]> wrote: Op 1-5-2020 om 08:35 schreef Roelof Wobben: You didn't actually ask a question :) btw, Its good you are stretching yourself to do it the most complicated way, but pay attention that when Richard says HE "likes code that traverses a data structure exactly once" its because he is starting with the philosophy to OPTIMISE for EFFICIENCY. Often in programming that is the LAST thing you should do because to do so your code often becomes more complex, and Kernagan's law applies... In general, you want to avoid premature optimization. The catch-phrase I see around this forum priorities things in this order: 1. Make it work. 2. Make it right. 3. Make it fast. and often you can stop at 2 because it is already "fast enough". Considering your code above, if I take TIME to go through it, I can evaluate that it seems right but I remain feeling that I could have missed something. Something like Richard's (A) examples without loops
I would consider to be "more good".
since each line can be dealt with individually. cardNumber := '4539 1488 0343 6467'. cleanDigits := cardNumber copyWithout: Character space. preWrapDigits := cleanDigits asArray collectWithIndex: [ :char :idx | (idx\\2 + 1) * char digitValue ]. wrappedDigits :=
preWrapDigits
collect: [ :d | d > 9 ifFalse: [ d ] ifTrue: [ d-9 ] ]. ^ wrappedDigits sum isDivisibleBy: 10. A side benefit is having full result of each transformation available to be reviewed, rather than having only pieces of it in view when you debug a loop. In the end though, yours is a good solution first and foremost because tried a more detailed way and you got it working!! Remember there is more than one "good way" to do it depending on what you are optimising for - efficiency or readability. cheers -ben |
Re: mentor question 4
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Op 2-5-2020 om 19:33 schreef Ben Coman:
I think I find readability more important then efficieny. But I think I have to alter your code. At first look it does not look like that every second value from the right is multiplied by 2. When the index is for example 7 . 7 // 2 gives 3. Maybe it needs to be %. Roelof |
Re: mentor question 4
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Op 2-5-2020 om 21:09 schreef Roelof Wobben via Pharo-users:
but this seems to work : cardNumber := '4539 1488 0343 6467'. cleanDigits := cardNumber copyWithout: Character space. preWrapDigits := (cleanDigits asArray reverse collectWithIndex: [ :char :idx | (idx even) ifTrue: [ 2 * char digitValue ] ifFalse:[char digitValue]]). wrappedDigits := preWrapDigits collect: [ :d | d > 9 ifFalse: [ d ] ifTrue: [ d-9 ] ]. ^ wrappedDigits sum isDivisibleBy: 10. Can the code be more improved ? Roelof |
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In reply to this post by Pharo Smalltalk Users mailing list
check with the finder and example
S.
-------------------------------------------- Stéphane Ducasse 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 |
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In reply to this post by Pharo Smalltalk Users mailing list
On Sat, May 2, 2020 at 12:38 PM Roelof Wobben via Pharo-users <[hidden email]> wrote: Op 2-5-2020 om 21:09 schreef Roelof Wobben via Pharo-users: As a general guideline, the best code will correspond closely to the documented algorithm. In this latest example, you have two
visible
loop iterations plus to hidden loop iterations. It also includes object creation from both #asArray and #reverse, the two messages with the hidden loop iteration. For this exercise, the number of loops and object creations isn't relevant. However, you always want to understand when you are doing such things. They will have an impact if they are used inside a high frequency loop. Again, that's not the case with this exercise. It often is in real world applications. But again, you should not optimize for performance at the expense of clarity and readability until you need to. And when you do need to, you annotate the code to explain how the implementation corresponds to or differs from the more comprehensible implementation. (Comments should explain the why and/or the background rather than the what.)
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In reply to this post by Ben Coman
On Sun, 3 May 2020 at 03:09, Roelof Wobben <[hidden email]> wrote:
But why are you testing // when my code uses \\ ? :) small details can have a big impact. cheers -ben |
Re: mentor question 4
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Op 3-5-2020 om 04:24 schreef Ben Coman:
Chips, but then it does exactly the other way around that I wanted. 7 is a non-even index 7 \\ 2 gives 1 + 1 gives 2 so the number gets multiplied by 2 where its must be multiplied by 1. 8 is a even index 8 \\ 2 gives 0 + 1 gives 1 so the number gets muliplied by 1 where it must be multiplied by 2. |
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In reply to this post by Ben Coman
On Sun., 3 May 2020, 3:48 pm Roelof Wobben, <[hidden email]> wrote:
Sorry, I worked from the example of your original post. where it looked like the odd indexes needed doubling and I was getting a checksum of 80 so that seemed correct. If you want to double the even indexes try (2 - (idx\\2)). cheers -ben |
Re: mentor question 4
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Op 3-5-2020 om 12:32 schreef Ben Coman:
oke, Then I have to assume that every credit card number has a even number of numbers. Roelof |
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In reply to this post by Pharo Smalltalk Users mailing list
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. |
LuhnTest.st (2K) |
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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 <[hidden email]> 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. |
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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 <[hidden email]> 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 <[hidden email]> 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 = $0 > --------------------------------- > Once this step is completed, the next step will be to make the code right without altering the algorithm (refactoring). The result should be readable and follow the team's conventions. > > > P.S. code attached. > > > -- > > The essence of object orientation is that objects collaborate to achieve a goal. > Trygve Reenskaug mailto: [hidden email] > Morgedalsvn. 5A http://folk.uio.no/trygver/ > N-0378 Oslo http://fullOO.info > Norway Tel: (+47) 468 58 625 |
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By the way, while playing with this problem, I ran into a moderately
painful issue. There is a reason that Smalltalk has both #printString (to get a printable representation of an object) and #asString (to convert a sequence to another kind of sequence with the same elements.) If I *want* #printString, I know where to find it. The definition in my Smalltalk no reads asString "What should #($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 Does anyone here know WHY Squeak and Pharo do what they do here? On Wed, 6 May 2020 at 01:20, Richard O'Keefe <[hidden email]> 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 <[hidden email]> 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 <[hidden email]> 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: [hidden email] > > Morgedalsvn. 5A http://folk.uio.no/trygver/ > > N-0378 Oslo http://fullOO.info > > Norway Tel: (+47) 468 58 625 |
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In reply to this post by Richard O'Keefe
I have forwarded a copy of the original message privately.
The problem is also described in RosettaCode. One issue is that the input is described in the original message and in the code I was responding to as "a number", but is in fact a string. On Wed, 6 May 2020 at 04:04, Trygve Reenskaug <[hidden email]> wrote: > > Unfortunately, I have lost the original problem specification, so I have answered a different question. Could you please help me by repeating the original problem specification in full? > > I agree that my solution is not 'obviously correct' since it doesn't answer the right question. In one version of the solution, I had a prologue that catered for spaces, etc. Not having a textual form of the algorithm that provided for the extensions, I chose to omit them. > > > > On tirsdag.05.05.2020 15:20, Richard O'Keefe 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 <[hidden email]> 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 <[hidden email]> 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 = $0 > --------------------------------- > Once this step is completed, the next step will be to make the code right without altering the algorithm (refactoring). The result should be readable and follow the team's conventions. > > > P.S. code attached. > > > -- > > The essence of object orientation is that objects collaborate to achieve a goal. > Trygve Reenskaug mailto: [hidden email] > Morgedalsvn. 5A http://folk.uio.no/trygver/ > N-0378 Oslo http://fullOO.info > Norway Tel: (+47) 468 58 625 > > > -- > > The essence of object orientation is that objects collaborate to achieve a goal. > Trygve Reenskaug mailto: [hidden email] > Morgedalsvn. 5A http://folk.uio.no/trygver/ > N-0378 Oslo http://fullOO.info > Norway Tel: (+47) 468 58 625 |
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In reply to this post by Richard O'Keefe
I was saying that I expected #($a $b $c) asString ==> 'abc'.
If you want something that can be read back, that's what #storeString is for, On Tue, 12 May 2020 at 01:28, Stéphane Ducasse <[hidden email]> wrote: > > > > On 5 May 2020, at 16:16, Richard O'Keefe <[hidden email]> wrote: > > By the way, while playing with this problem, I ran into a moderately > painful issue. > > There is a reason that Smalltalk has both #printString (to get a > printable representation of an object) and #asString (to convert a > sequence to another kind of sequence with the same elements.) If I > *want* #printString, I know where to find it. The definition in my > Smalltalk no reads > > asString > "What should #($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 $c)' > - GNU Smalltalk, Smalltalk/X, and astc: > 'abc' > I don't intend any gratuitous incompatibility, but when there > is no consensus to be compatible with, one must pick something, > and this seems most useful. > " > ^String withAll: self > > Does anyone here know WHY Squeak and Pharo do what they do here? > > > Oops I did not see the quotes on my screen.. > > #( a b c) asString > >>> '#(#a #b #c)’ > > this is unclear to me why this is not good but I have no strong opinion > that this is good. > > I worked on printString for literals because I wanted to have > self evaluating properties for basic literal like in Scheme and others. > where > #t > >>> > #t > > And I payed attention that we get the same for literal arrays. > Now the conversion is open to me. > > #($a $b $c) asString > >>> > '#($a $b $c)’ > > In fact I do not really understand why a string > > #($a $b $c) asString would be '(a b c)’ > and its use > if this is to nicely display in the ui I would have > displayString doing it. > > S. > > > > On Wed, 6 May 2020 at 01:20, Richard O'Keefe <[hidden email]> 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 <[hidden email]> 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 <[hidden email]> 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 = $0 > --------------------------------- > Once this step is completed, the next step will be to make the code right without altering the algorithm (refactoring). The result should be readable and follow the team's conventions. > > > P.S. code attached. > > > -- > > The essence of object orientation is that objects collaborate to achieve a goal. > Trygve Reenskaug mailto: [hidden email] > Morgedalsvn. 5A http://folk.uio.no/trygver/ > N-0378 Oslo http://fullOO.info > Norway Tel: (+47) 468 58 625 > > > > -------------------------------------------- > Stéphane Ducasse > http://stephane.ducasse.free.fr / http://www.pharo.org > 03 59 35 87 52 > Assistant: Julie Jonas > FAX 03 59 57 78 50 > TEL 03 59 35 86 16 > S. Ducasse - Inria > 40, avenue Halley, > Parc Scientifique de la Haute Borne, Bât.A, Park Plaza > Villeneuve d'Ascq 59650 > France > |
Re: mentor question 4
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On May 11, 2020 2:19:49 PM PDT, Richard O'Keefe <[hidden email]> wrote: >I was saying that I expected #($a $b $c) asString ==> 'abc'. Over the years, I found myself being opposed to the idea that all objects can sensibly have an #asString implementation. When it's been done, it ultimately caused more problems than it solved. Consider $(48 49 50) asString. Do you expect it to give you a string with all the digits? Or perhaps it's meant to interpret the elements as byte-like things, as you would need for "String withAll: aCollection". So, the numbers could be interpreted as codepoints, as they are in a ByteArray. But, what does "(Array with: Object new with: ProcessScheduler) asString" mean? It seems to me that having all objects understand #asString leads to confusion. If you want an array to print as its literal representation, implement #printAsLiteral, so that your intention is clear. >If you want something that can be read back, that's what #storeString >is for, > >On Tue, 12 May 2020 at 01:28, Stéphane Ducasse ><[hidden email]> wrote: >> >> >> >> On 5 May 2020, at 16:16, Richard O'Keefe <[hidden email]> wrote: >> >> By the way, while playing with this problem, I ran into a moderately >> painful issue. >> >> There is a reason that Smalltalk has both #printString (to get a >> printable representation of an object) and #asString (to convert a >> sequence to another kind of sequence with the same elements.) If I >> *want* #printString, I know where to find it. The definition in my >> Smalltalk no reads >> >> asString >> "What should #($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 $c)' >> - GNU Smalltalk, Smalltalk/X, and astc: >> 'abc' >> I don't intend any gratuitous incompatibility, but when there >> is no consensus to be compatible with, one must pick something, >> and this seems most useful. >> " >> ^String withAll: self >> >> Does anyone here know WHY Squeak and Pharo do what they do here? >> >> >> Oops I did not see the quotes on my screen.. >> >> #( a b c) asString >> >>> '#(#a #b #c)’ >> >> this is unclear to me why this is not good but I have no strong >opinion >> that this is good. >> >> I worked on printString for literals because I wanted to have >> self evaluating properties for basic literal like in Scheme and >others. >> where >> #t >> >>> >> #t >> >> And I payed attention that we get the same for literal arrays. >> Now the conversion is open to me. >> >> #($a $b $c) asString >> >>> >> '#($a $b $c)’ >> >> In fact I do not really understand why a string >> >> #($a $b $c) asString would be '(a b c)’ >> and its use >> if this is to nicely display in the ui I would have >> displayString doing it. >> >> S. >> >> >> >> On Wed, 6 May 2020 at 01:20, Richard O'Keefe <[hidden email]> >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 <[hidden email]> >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 <[hidden email]> >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: [hidden email] >> 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 >> |
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Hi all,
I’ve been lurking so far, but I must add my voice here and agree with Richard. The malleability of Smalltalk tempts people into implementing #asString, #name, and similar semantically ambiguous method names. Like Richard, I regretted every single time I (or someone else on my team before me) decided to use these. It goes back to ’Smalltalk with Style’ (probably the best little red book you could ever own): write intention revealing code whenever you can, and comment liberally when you can’t.
Jerry Kott This message has been digitally signed. PGP Fingerprint: A9181736DD2F1B6CC7CF9E51AC8514F48C0979A5
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For what it's worth, here's a moderately thorough examination of several different Smalltalk systems. Let A = astc, D = Dolphin, G = GNU Smalltalk, Q = Squeak, S = ANSI standard, T = Strongtalk, V = VisualWorks, X = ST/X #asString ADGPQST!X Character => String with: self ADGPQSTVX String => self ADGPQSTVX Symbol => String withAll: self ......... Text/Paragraph, where provided, => underlying string. A-G-----X Collection => String withAll: self ---PQ---- Collection => self printString A........ ByteArray => "decoded as Unicode" .DGPQ-TVX ByteArray => "decoded as Latin1" ADG.Q..VX Filename => "unparse (Filename, FilePath, whatever) AdgpQ.TVX URI => "unparse (ZnUrl in P) Ad.PQ...X UUID => "unparse (d, GUID equivalent)" .DGpq...X Number => self displayString "or self printString, maybe via Object" ...PQ...X Object => self printString There's a rough consensus here: - if something *is* textual (Character, String, Symbol, Text, Paragraph) #asString returns it as a normal string - if something is a parsed form of structured text (file name, URI, UUID) its unparsed form is returned, converting it back should yield an equal parsed form - if something is a byte array, it may be converted to a string (the rule is to preserve the bytes, my library presumes byte arrays are UTF8-encoded) - if numbers are accepted at all, their #printString is returned - if is none of the above, but has a #name or #title, that is commonly the result. The open question is what converting an array of characters using #asString will do. There is at least one Smalltalk out there where #(65 66 67) asString => 'ABC', but that's a step further than I personally want, though it is consistent with ByteArray. On Tue, 12 May 2020 at 11:16, Jerry Kott <[hidden email]> wrote:
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Re: mentor question 4
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Richard, your diligence is awesome!
I'm left feeling that, generally, objects should not implement nor understand #asString. I realize there is a lot of room for debate on this subject. On May 11, 2020 10:12:10 PM PDT, Richard O'Keefe <[hidden email]> wrote:
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