May 2020 - Pharo-users - lists.pharo.org

Re: [Pharo-users] mentor question 4
by Richard O'Keefe May 2, 2020

May 2, 2020

This sounds very much like the Luhn test task at RosettaCode. https://rosettacode.org/wiki/Luhn_test_of_credit_card_numbers except that there it is described as working on the digits of an integer. (1) There are two approaches to traversing a sequence in reverse. (A) Reverse the sequence, then traverse the copy forward. aString reverse do: [:each | ...] (B) Just traverse the sequence in reverse aString reverseDo: [:each | ...] My taste is for the second. (2) There are two approaches to deleting spaces. (A) Make a copy of the string without spaces. x := aString reject: [:each | each = Character space]. x do: ... (B) Ignore spaces as you go: (i) aString do: [:each | each = Character space ifFalse: [...]] (ii) aString select: [:each | each ~= Character space] thenDo: [:each | ...] Combining (1A) and (2A) you get very obvious code: (aString reject: [:each | each = Character space]) reverse do: [:digit } ...] Combining (1B) and (2Bi) you get more efficient code: aString reverseDo: [:digit | digit = Character space ifFalse: [ ...]] By the way, let's start by checking that the character in the string *are* digits or spaces: (aString allSatisfy: [:each | each isDigit or: [each = Character s[ace]]) ifFalse: [^false], (3) There are two approaches to doubling the even digits. (A) Make a new string that starts as a copy and change every second digit from the right. (B) Simply *act* as if this has been done; keep track of whether the current digit position is even or odd and multiply by 1 or 2 as appropriate. nextIsOdd := true. aString reverseDo: [:digit | digit = Character space ifFalse: [ nextIsOdd ifTrue: [oddSum := ...] ifFalse: [evenSum := ...]. nextIsOdd := nextIsOdd not]]. I *like* code that traverses a data structure exactly once and allocates no intermediate garbage, so I'd be making (B) choices. But I am not at all sure that it is right for *you* at this stage. Your goal is to get practice in making code that is obviously correct and lends itself to testing. I think in your case it makes more sense to make the (A) choices. You can write some code that reverses a string (using the built-in method) and test that it does what you expect. You can write some code that checks whether a string contains only digits and spaces, and test that. You can write some code that returns a space-less copy, and test that. You can write some code that returns the even (odd) elements of a sequence, and test those. SequenceableCollection>> withIndexSelect: aBlock |index| index := 0. ^self select: [:each | aBlock value: each value: (index := index + 1)] evenElements ^self withIndexSelect: [:each :index | index even] oddElements ^self withIndexSelect: [:each :index | index odd] The easiest way to convert a string to numbers and add up the numbers is to use #detectSum, as in aString oddElements detectSum: [:char | char digitValue] How do you find #digitValue? By looking in Character. #detectSum:? Collection enumeration methods. Using the (A) approach will give you lots of little methods, which you can comment and above all TEST, so that each mistake will be in just one small method. This is a typical functional programming "lots of little functions" approach. On Thu, 30 Apr 2020 at 18:33, Roelof Wobben via Pharo-users <pharo-users(a)lists.pharo.org> wrote: > > Hello, > > I hope I can discuss my approch to this problem : > > Given a number determine whether or not it is valid per the Luhn formula. > > The Luhn algorithm is a simple checksum formula used to validate a variety of identification numbers, such as credit card numbers and Canadian Social Insurance Numbers. > > The task is to check if a given string is valid. > > Validating a Number > > 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. > > Example 1: valid credit card number > > 4539 1488 0343 6467 > > The first step of the Luhn algorithm is to double every second digit, starting from the right. We will be doubling > > 4_3_ 1_8_ 0_4_ 6_6_ > > If doubling the number results in a number greater than 9 then subtract 9 from the product. The results of our doubling: > > 8569 2478 0383 3437 > > Then sum all of the digits: > > 8+5+6+9+2+4+7+8+0+3+8+3+3+4+3+7 = 80 > > If the sum is evenly divisible by 10, then the number is valid. This number is valid! > > > my idea was to do these steps > > 1) reverse the input. > > 2) use this to double every second digit and calculate the sum of all the numbers : > > checkNumber := (collection reverse selectwith index: [:item :index | (index % 2 == 0) . IfTrue: [item *2]] ) sumNumbers > > 3) check if its a valid number by doing this : > > > ^ (checkNumber % 10 == 0) > > > is this a good game plan or has it flaws or can I do it better ? > > Regards, > > > Roelof > >

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Package Browser (AKA 6-paned Browser) and Pharo package organization
by stephen＠heaveneverywhere.com May 1, 2020

May 1, 2020

Hello friends, Iâm getting started with Pharo after decades using VisualWorks and Squeak; itâs pretty wonderful what you all have assembled! My question is related to what we used to teach as the first law of software reuse: âYou canât reuse it if you canât find it,â and the related software engineering "principle of least astonishment." When I fire up Pharo, the system browser presents me with a list of several hundred categories (from AST to Zodiac) in a system with over 8000 classes. The system categorization makes no sense since I donât know the naming conventions and so many packages have cute but quite non-descriptive names (Zinc? Metacello? Calypso?). In Smalltalk-80, the class category names were organized as a 2-level hierarchy where the top-level were items such as Magnitudes, Collections, Streams, Graphics, Text, System, Tools, Files, etc. This made it easy to find (e.g.,) the browser source code by looking in the Tools package for the class category Tools-Browser. Even packages with cute names (like my own âSirenâ), were categorized for ease of finding; e.g., the Siren classes were in class categories like Music-Events and Music-Magnitudes. Parsing the class category names on the first instance of $- made it possible to build 6-paned Browsers (called package pane browser in Squeak). (We acknowledged that this violates the âzero/one/infinity" rule.) Is something like this available for Pharo? I looked through the Calypso browser code and itâs so over-engineered (IMHO) that itâd take me several days to figure out how to implement this (it was about 1.5 pages of code in Smalltalk-80). If Pharo had a browser that scaled better and a reorganization/simplification of the class categories to use names that were more self-explanatory, it would be *much* easier for new users (in fact, for all users) to find their way around. I apologize for the stepping on toes... Stephen Pope -- Stephen Travis Pope Santa Barbara, California, USA http://HeavenEverywhere.com <http://heaveneverywhere.com/> http://FASTLabInc.com <http://fastlabinc.com/> https://vimeo.com/user19434036/videos <https://vimeo.com/user19434036/videos> http://heaveneverywhere.com/Reflections --

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Automating release announcements
by Gabriel Cotelli May 1, 2020

May 1, 2020

Hi!, Anyone here is moderator in the Pharo Users list? I want to automate the release announcement of projects in github/ba-st org. I'm using sendgrid to send the e-mails and I'm getting a returning mail saying: "Your message to Pharo-users awaits moderator approval". I subscribed previously to the list the e-mail account used as mail sender. Thank you for your help! Gabriel

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