[Part 2 of the HP Calc series ] Making the JavaScript-based HP-35 microcode emulator has been a fun little project. Last time we disassembled the original bits from the ROM. I say “disassemble” but really our microcode instructions were...

[Part 1 of the HP Calc series ] I recently started a super-geeky side hobby of collecting vintage calculators and got my hands on a pair of HP calcs. The more I learned about the internals of the devices, the more intrigued I was. Jacques Laporte...

[Part 1 of the FScheme series ] One of my New Year’s goals is to re-read Lisp in Small Pieces and implement all 11 interpreters and 2 compilers. As much as I like the "Lisp in Lisp" idea and enjoyed the eureka moment in SICP when Sussman writes...

First ten digits of sum of following one-hundred 50-digit numbers. It would be interesting to do without BigInts. Could use doubles with enough precision for just the first ten digits or some such thing, but just wanted the correct answer to plug into...

First triangle number to have over five hundred divisors. let naturals = Seq.unfold ( fun i -> Some(i, i + 1)) 1 // from prob7 let triangleNums = Seq.scan (+) 0 naturals let isFactor n d = n % d = 0 let factors n = seq { 1..int (sqrt (float n))...

Greatest product of four adjacent numbers (up, down, left, right, or diagonally) in this 20x20 grid: let grid = [|08;02;22;97;38;15;00;40;00;75;04;05;07;78;52;12;50;77;91;08; 49;49;99;40;17;81;18;57;60;87;17;40;98;43;69;48;04;56;62;00; 81;49;31;73;55;79;14;29;93;71;40;67;53;88;30;03;49;13;36;65;...

Sum of primes below two-million. Easy problem, but way too slow (taking several minutes) with the naïve prime number generator from problem 7 . This new version is 10x faster, based on this paper: http://www.cs.hmc.edu/~oneill/papers/Sieve-JFP...

Pythagorean triplet where a + b + c = 1000 (2, 1) |> Seq.unfold ( fun (m, n) – >     Some([m * m - n * n; 2 * m * n; m * m + n * n],         if n + 1 < m then m, n + 1 else m + 1, 1)) |> Seq...

Largest products of five consecutive digits in this 1000-digit number. open System.Numerics let digits n = Seq.unfold ( fun i – > if i = 0I then None else Some(i % 10I, i / 10I)) n let consecutive = Seq.unfold ( function (a : BigInteger) ...

What do you think this “code” does? 0(1adf89r)720x Well, it’s a ridiculously terse, stack-based Logo-like language with single character commands. Beginning with 0, it repeatedly (720 times) increments the top stack value and moves forward by that amount...

Stephen Wolfram ’s book, “ A New Kind of Science ” is flippin’ brilliant! (or perhaps I'm just not brilliant enough to realize he's a mad man) 1,280 pages packed with beautiful insights and Tufte-worthy visualizations. I remember...

[Part 14 of the FScheme series ] Historical Debugging in VS2010 is quite the engineering feat! We can actually pull off something similar in our interpreter with amazing ease. Because of the pure nature of our functional I/O system (last two posts...

[Part 13 of the FScheme series ] Now to add input to our Functional I/O system; following up on the previous post . We already had bouncing balls so how ‘bout we add a mouse-controlled paddle and make a primitive “Pong”? Mouse...

[Part 12 of the FScheme series ] I just watched Matthias Felleisen’s talk on Functional I/O and read this paper and decided to bolt on a little I/O system to the FScheme interpreter we’ve been building. It’s a pretty nice FRP-type...

[Part 11 of the FScheme series ] We’re now taking the first small step into the world of nondeterministic logic programming (chapter 16 of Bill Hails’ book ). Hopefully you enjoyed the last post about continuation passing and found the...

[Part 10 of the FScheme series ] We’re into one of the most magical chapters in Bill Hails’ book . We’re about to add a very strange and dangerous feature to the interpreter: ‘call/cc’ (“call with current continuation”...

I remember the strange feeling as a kid the first time I saw structured BASIC after having been doing everything with line numbers. Any time I happened to walk into a Radio Shack in the early 80s I’d just have to leave this behind:   I was in a GOTO...

[Part 9 of the FScheme series ] Primitives Perhaps this post should have gone along with the one about macros and how Lisp is a “programmable programming language.” The common tension in any language or runtime design is how much to...

[Part 8 of the FScheme series ] 'set', 'begin', 'define' Here we implement chapters 10 and 11 of Bill Hails’ book . We’re about to do something hideous and horrible to the language (and to our interpreter). We’re about to add assignment...

[Part 7 of the FScheme series ] The Soul of Scheme We’re now getting into the language-oriented features of Scheme. This is why Scheme is one of my very favorite languages. Scheme is of course a multi-paradigm language; functional, imperative...

[Part 6 of the FScheme series ] Once again, I must plug Bill Hails’ book Lists How could we even be pretending this is Lisp when we have yet to add lists! We need to add the standard ‘cons’, ‘car’, and ‘cdr’...

[Part 5 of the FScheme series ] In this series I’m glossing over all the gory details. You really should read Bill Hails’ book ! Simultaneous 'let' We just added ‘letrec’ to solve the issue of bindings referring back to...

[Part 4 of the FScheme series ] Recursive ‘let’ Normal ‘let’ can’t be used to bind names to recursive expressions (ones referring back to the names) because the expressions end up being evaluated in the calling environment...

[Part 3 of the FScheme series ] Continuing along in Bill Hails’ book . Be sure to follow the previous posts . Lambda Now we’re going to add the all-powerful ‘lambda’! Since we’ve already done all the environment...

[Part 2 of the FScheme series ] Still working through Bill Hails’ awesome book . Adding to the FScheme interpreter from this previous post . Now we’ll add ‘let’. To do this we’re changing the evaluation model into an environment...