Dyalog v20.0 introduced a new operator, behind (⍛). Silas explains some of the processes involved in adding a new language element like an operator, using the behind operator and the lessons learnt during its implementation as a reference.

APL enables knowledgeable people to express solutions as simple, direct, code. In an ideal world, we could live in the Session, elegantly transforming from array to array. In the real world, we often need additional expertise to interface with other technologies, to utilise existing solutions, or to make our own accessible to less technical end users.

In APL, quad (⎕) denotes the machine and can be thought of as the window to the outside world. System functions have long been the primary mechanism for that interfacing. At their best, they are simple enough for a domain expert to build an entire system unaided. However, their limits are the implementor's limits, and beyond those you still need to know the external technology. Large Language Model (LLM)-assisted development is now lowering that barrier; Rich and Mark demonstrate examples of APL development and interfacing work accelerated by LLM assistance.

EWC is Dyalog's cross-platform implementation of the ⎕WC GUI family. Your APL applications are constructed using the same forms as under ⎕WC; EWC renders them as a real GUI on Linux, macOS, or Microsoft Windows, either in a desktop window or a browser tab.

Aarush demonstrates how EWC works; his demonstration includes examples of applications that have already been re-platformed without changes and others that have been built using EWC from the start. He explains what's changed since Morten’s Dyalog ’24 presentation on EWC, and shares the plan for the future.

The workspace is 60 years old, and at Dyalog '18, Paul Mansour declared it dead. Adám reviews the decade since. He traces the history of APL source – from binary workspaces and ⎕ORs in component files, through transfer files and SALT's scripted namespaces, to Link, Acre, Cider, Tatin, and Git – and shows how the interpreter has taken over jobs that once needed a bootstrap workspace. He considers what the workspace is still good for, and looks ahead to modules, single-file source, and source handling built into the interpreter.

Mikaela describes the process, difficulties, and upsides of learning APL, as well as the mindset behind learning to apply artistic creativity to technology while creating a video game.

It can be difficult for professional users to make time to learn about everything happening in the world of Dyalog. The user meeting offers a great opportunity, but there's no need to wait for the next one to learn about new features, projects, and techniques. Rich provides an overview of what APLers have been saying and doing in this whirlwind tour of APL community projects and publications.

Tacit programming is a paradigm in which the programmer, rather than writing a dfn or tradfn that explicitly references arguments, builds a single derived function and relies on operators and trains to control the flow of arguments. While purely tacit programming is best used only for recreational confusion, everyone uses derived functions. Max demonstrates common idioms that he uses – split, inspect, read, write, and select. He explains how they're useful to him, and summarises the tools and resources that help him to write tacit code.

Co-dfns is an APL compiler that is designed to let a programmer use APL in more places and for more applications. When compared with the stadard Dyalog interpreter, it can enable better integration with other programming environments and high-performance domains (such as scientific computing, machine learning, and graphics), and improved performance in certain situations. A lot has been happening with the Co-dfns compiler since Aaron’s last update at Dyalog ‘24; he introduces the new version 6 release and provides a roadmap of what's next on the horizon for APL compilation.

Many everyday APL expressions are longer than they need to be. Adám presents a draft proposal for eight small language changes, each of which shortens a common idiom: monadic ≤ and ≥ to sort ascending and descending, monadic ∧ and ∨ to promote and demote rank, monadic ⊤ and ⊥ to encode and decode binary, monadic ⊇ (a companion to monadic ⊃) to pick the last, and an extension to dyadic ⍴ allowing one axis length to be inferred. He demonstrates each in use and invites discussion.

Every Dyalog release is preceded by a lot of testing that users never see. Aarush introduces through the test suites that run continuously against the interpreter: the long-standing unit tests, ullu's primitive-by-primitive tests, coverage-instrumented builds that report exactly which lines of the interpreter's C source each suite exercises, and fuzzing, which compiles an instrumented interpreter and then spends entire weekends inventing APL expressions designed to crash it. Crashes are automatically minimised, deduplicated, and added to a growing body of tests that are replayed against every platform and edition on later builds.

He then introduces CITA, which lets our APL tools be tested against many interpreter versions, editions, and platforms on real hardware.

Aarush concludes by looking at the testing of GUIs, which have always been the part everyone struggles to automate. He demonstrates how EWC and ⎕WC are now covered by several hundred tests with pixel-tight visual regression running on every pull request. Much of this suite was written by LLM agents exploring the running application, and he concludes with his thought on this approach might change the way in which test suites are built and maintained.

It is usually convenient to represent data visually, for example, as a table or as some kind of technical plot, and Dyalog already offers several options for doing this. Jesús introduces a different approach that uses some of Dyalog APL’s features: user commands are organised in Tatin packages, configuration options and data are defined as namespaces, and external JavaScript libraries take care of the actual rendering. As a lighter option, a text-based alternative renderer is provided, which makes it possible to display simple plots and tables directly in your session in any environment.

Dyalog Ltd's Managing Director closes the user meeting.