John Scholes

Geoff Streeter – Celebrating 40 Years with Dyalog

A personal account by John Scholes As a relatively new arrival to Dyalog, I have been working with Geoff for only 35 of his 40 years in the company, although we met earlier when we both worked for Atkins Computing in the early 1970s. Our in-depth collaboration started in the autumn of 1981, when we got together … Read

Apr 2017
in Team Dyalog

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 ⍝ … Read

May 2016
in APL Language, Musings, Tips & Tricks

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 … Read

Jul 2015
in APL Language, Musings

Name Colouring for Dfns

APL is sometimes criticised because expressions that include names cannot, in general, be parsed without knowing whether the names represent functions or variables. For example, the name thing in the expression thing⍳3 could reference an array (in which case the ⍳ is dyadic) or it could reference a function (making the ⍳ monadic). An APL … Read

May 2015
in APL Language, Musings

Foo, Shmoo

“We do not realize what tremendous power the structure of an habitual language has. It is not an exaggeration to say that it enslaves us through the mechanism of s[emantic] r[eactions] and that the structure which a language exhibits, and impresses upon us unconsciously, is automatically projected upon the world around us.” —Korzybski (1930) in … Read

Feb 2015
in APL Language, Musings

Musings on Reduction

In one man’s humble opinion, reduction (⌿) is the Queen of Operators. Each (¨) comes a close second, but doesn’t get the cigar because each can be written in terms of reduction. Two special cases are of interest: reduction along axes of length 1 (or reduction of a scalar) and reduction along axes of length … Read

Nov 2014
in APL Language, Musings

Selective Expression Tracing

Operator trace from dfns.dws is a simple and low-tech tool for displaying intermediate results of functions, during the evaluation of an expression. For example, what’s going on here? (+⌿ ÷ ≢) 1 2 3 4 2.5 We can guess that the above fork is computing the average of the right argument. To see how this works: )copy dfns … Read

Oct 2014
in APL Language

Data-driven Conditionals

ACKNOWLEDGEMENT: My thanks to Andy Shiers for simplifying the examples Visitors to APL from other languages are sometimes a bit sniffy about our use of numbers (1 0) for Boolean values True and False. They’re further bemused by our fondness for moving conditional processing out of code and into data. For example, instead of: 0=2|⍵: … Read

Oct 2014
in APL Language

Genius, Gentleman and Mischievous Schoolboy

Geoff Streeter – Celebrating 40 Years with Dyalog

Loops, Folds and Tuples

Type Comments

Name Colouring for Dfns

Foo, Shmoo

Musings on Reduction

Selective Expression Tracing

Data-driven Conditionals

Return to the Robot

By

Morten Kromberg

Building a Web Application with MiServer

By

Dyalog Ltd

What’s Your Favourite Beautiful Squiggle?

By

Fiona Smith

Monday at Dyalog ‘15

By

Dyalog Ltd