Mind Boggling Performance
or is it Minding Boggle Performance? In the 2019 APL Problem Solving Competition, we presented a problem to solve the Boggle game where a player tries to make as many words as possible from contiguous letters in a 4×4 grid with the stipulation that you cannot reuse a position on the board. Richard Park’s 17 […]
Enhanced Debugging with Function Keys – Evaluate selection
See also Enhanced Debugging with Function Keys. When tracing through a complex dfn and reaching a guard (condition:result), I am often wary of tracing into that line because if the condition evaluates to 1 then the current function I’m tracing through will terminate and return the result, leading to me losing situational awareness. Normally, I’d […]
Towards Improvements to Stencil
Background The stencil operator ⌺ was introduced in Dyalog version 16.0 in 2017. Recently we received some feedback (OK, complaints) that (a) stencil does padding which is unwanted sometimes and needs to be removed from the result and (b) stencil is too slow when it is not supported by special code. First, stencil in cases […]
Enhanced Debugging with Function Keys
Sometimes I want an additional functionality in the IDE. (Are you a RIDE user? We’ll cover that too!) For example, the other day, I was tracing through some very long functions to find an error which was being caught by a trap. Since the error was being caught, I couldn’t just let the function run […]
I-Beam Mnemonics
I-Beam (⌶) is an operator that takes as its operand a numeric code and derives a function which isn’t really considered to be part of the APL language – for example: something which could be experimental, which might provide access to parts of the interpreter that should only be accessed with care, or may set […]
Loops, Folds and Tuples
For-loops Given an initial state defined by a number of variables, a for-loop iterates through its argument array modifying the state. A←… ⋄ B←… ⋄ C←… ⍝ initial state :For item :In items ⍝ iterating through array “items” A←A … item ⍝ new value for A depending on item C←C … A … item ⍝ new value for C depending on A and item … ⍝ state updated :EndFor A B C ⍝ […]
Quicksort in APL Revisited
A message in the Forum inquired on sorting strings in APL with a custom comparison function. First, sorting strings without a custom comparison function obtains with a terse expression: {⍵[⍋↑⍵]} ‘syzygy’ ‘boustrophedon’ ‘kakistocracy’ ‘chthonic’ ┌─────────────┬────────┬────────────┬──────┐ │boustrophedon│chthonic│kakistocracy│syzygy│ └─────────────┴────────┴────────────┴──────┘ Sorting strings with a custom comparison function can also be accomplished succinctly by simple modifications to the Quicksort […]
Zero-length Regular Expression Matches Considered Harmful
I was asked by a colleague why ⎕S reports two matches in the following example: (‘\d*’⎕S 0 1)’321’ ┌───┬───┐ │0 3│3 0│ └───┴───┘ Here we are asking for the position and length of sequences of zero or more digits in an input document containing three numeric characters. Intuitively there is just one match of all […]
Three-and-a-bit
The most obvious expression for computing π in APL is ○1. But what if you can’t remember how ○ works, or your O key is broken, or you feel like taking the road less travelled? With thanks to Wikipedia’s excellent list of Approximations of π, here are some short sweet APL expressions for three-and-a-bit: 3 ⍝ very short […]
Solving the 2014 APL Problem Solving Competition – it's as easy as 1 1 2 3…
The winners of the 2014 APL Problem Solving Competition were recognized at the Dyalog ’14 user meeting and had a chance to share their competition experiences. Emil Bremer Orloff won the student competition and received $2500 USD and an expenses-paid trip to Dyalog ’14, while Iryna Pashenkovska took first place among the non-student entries and received a complimentary […]
A Speed-Up Story
The first e-mail of the work week came from Nicolas Delcros. He wondered whether anything clever can be done with ∘.≡ on enclosed character strings. I immediately thought of using “magic functions“, an implementation technique whereby interpreter facilities are coded as dfns. I thought of magic functions because the APL expressions involved in this case […]
Creating Shortcuts (Microsoft Windows)
At Dyalog, a developer not only needs access to all of the readily available editions of the interpreter but also to earlier versions that are no longer officially supported. On my Microsoft Windows Desktop I have a folder that contains a shortcut to my developer builds of all these interpreters. I’ve recently suffered a complete […]
