When you consider the age old problem of representing different shapes (circle, triangle, square, rectangle, etc.) my OO fed developer brain naturally jumps to a class hierarchy along the line of: This is perfectly fine and legit, but it’s not the only way to approach things. Since I’ve been on a more varied diet of …
F# – Use Discriminated Unions instead of class hierarchies Read More »
C# developers should be familiar with the yield keyword that was introduced in C# 2.0, and you’ll be pleased to know that F# also has the yield keyword which works in conjunction with F#’s equivalent of IEnumerable – sequences. You can create sequences in F# using sequence expressions: In addition, you can also use the …
In F#, you can defined record types which differ from tuples and discriminated unions in that they allow you to organize values into a type and name those values through fields: Looks like a cut-down version of a standard .Net class with a couple of properties? Yes they do, but records offer several advantages over …
I’m taking a bit of time to brush up my knowledge of F# and see if I can write better F# code and one of the things I notice is that whilst I use pipe-forward operator (|>) often when working with collections I don’t nearly use the pipe-backward operator (<|) as frequently as I should. …
Problem Each character on a computer is assigned a unique code and the preferred standard is ASCII (American Standard Code for Information Interchange). For example, uppercase A = 65, asterisk (*) = 42, and lowercase k = 107. A modern encryption method is to take a text file, convert the bytes to ASCII, then XOR …
Problem A common security method used for online banking is to ask the user for three random characters from a passcode. For example, if the passcode was 531278, they may ask for the 2nd, 3rd, and 5th characters; the expected reply would be: 317. The text file, keylog.txt, contains fifty successful login attempts. Given that …
Problem Some positive integers n have the property that the sum [ n + reverse(n) ] consists entirely of odd (decimal) digits. For instance, 36 + 63 = 99 and 409 + 904 = 1313. We will call such numbersreversible; so 36, 63, 409, and 904 are reversible. Leading zeroes are not allowed in either …
Problem The number 145 is well known for the property that the sum of the factorial of its digits is equal to 145: 1! + 4! + 5! = 1 + 24 + 120 = 145 Perhaps less well known is 169, in that it produces the longest chain of numbers that link back to …
Problem Peter has nine four-sided (pyramidal) dice, each with faces numbered 1, 2, 3, 4. Colin has six six-sided (cubic) dice, each with faces numbered 1, 2, 3, 4, 5, 6. Peter and Colin roll their dice and compare totals: the highest total wins. The result is a draw if the totals are equal. What …
Problem By counting carefully it can be seen that a rectangular grid measuring 3 by 2 contains eighteen rectangles: Although there exists no rectangular grid that contains exactly two million rectangles, find the area of the grid with the nearest solution. Solution This problem looks more difficult than it is, I’m not going to go …
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