Shuffle Faster Please!
Andy reported that in the shuffle QA some functions take a long time: m9249 “4½ days so far” rankop 21.5 hours m12466 26.3 hours points 7.2 hours Background: Shuffle QA is an intensification of the normal QA. The suite of over 1800 QA functions is run under shuffle, whereby every getspace (memory allocation) is followed by every APL array […]
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 […]
Response to Feedback on Cut, Under and Merge
At Dyalog ’15 John Scholes and I presented proposals for future operators cut, under, and merge. Following the release of the video of this presentation, we received some feedback from a user. Our response to the feedback may be of wider interest. It’s early days yet for cut, under, and merge (they are tentatively planned […]
The Reflex/Commute Operator
The monadic operator ⍨ is defined and modeled as follows: f⍨ ⍵ ←→ ⍵ f ⍵ ⍺ f⍨ ⍵ ←→ ⍵ f ⍺ {⍺←⍵ ⋄ ⍵ ⍺⍺ ⍺} Reflex Some common well-known functions can be written as f⍨ where f is itself a well-known function: +⍨ double ×⍨ square ?⍨ […]
Parallel Programming with Futures/Isolates
Morten Kromberg went right to it with his well-prepared workshop on the prototype features that were introduced in version 14.0 of Dyalog APL. The features are still partly modelled in APL to allow the first wave of users to pass judgement on the design. Throughout the workshop, we were asked for feedback, to ensure that […]
Permutations
I started composing a set of APL exercises in response to a query from a new APL enthusiast who attended Morten’s presentation at Functional Conf, Bangalore, October 2014. The first set of exercise are at a low level of difficulty, followed by another set at an intermediate level. One of the intermediate exercises is: Permutations […]
Type Comments
I’ve taken to commenting the closing brace of my inner dfns with a home-grown type notation pinched from the Functional Programming community: dref←{ ⍝ Value for name ⍵ in dictionary ⍺ names values←⍺ ⍝ dictionary pair (names⍳⊂⍵)⊃values ⍝ value corresponding to name ⍵ } ⍝ :: Value ← Dict ∇ Name I keep changing my […]
In Praise of Magic Functions: Part II
Part I of this post was concerned with the development speed and execution speed of magic functions and should be read before this post. Benefitting from Future and Past Improvements Looking at the magic function for key in Part I, we see that its performance depends on the following APL primitives, listed with information on […]
In Praise of Magic Functions: Part I
A magic function is an APL-coded (dfn) computation in the C source of the interpreter. For example, some cases of ∧.= are coded as MAGIC(“(≢⍺)(↑∘.=↓)⍺⍳⍺⍪⍉⍵”). The rubric “magic function” includes magic functions and magic operators. Acknowledgments. Magic functions in Dyalog are made possible due to work done by John Scholes and Richard Smith. Development Speed […]
