GendL Introduction

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What is GendL?

GendL is a dynamic, declarative, object-oriented language environment embedded in ANSI Common Lisp (CL). It consists of a collection of predefined objects, code-expansion macros, and functions which you, the GendL application developer, may either use directly or extend, to solve problems of any level of complexity decomposed into manageable units. GendL includes geometric primitives (wireframe, surfaces and solids) and has a built-in web server to facilitate cross-platform deployment. Unlike many other programming languages which execute procedurally line by line, GendL only evaluates expressions when they are demanded, and the object, slot, and function specifications within an object definition can be written in any order. Another useful and distinguishing feature is GendL's built-in runtime dependency tracking. This allows your applicaton code to make modifications to the value of any slot at runtime, and the GendL runtime system will immediately mark any downstream dependent slots as "Unbound", forcing them to be re-computed with fresh data the next time they are demanded.

GendL development tools

Emacs IDE

GendL is provided with a configuration for the Emacs Integrated Development Environment (IDE) called "Slime", or the "Superior Lisp Interaction Mode for Emacs." Although any text editor can be used, the Emacs/Slime combination provides a rich and evolving set of features for developing GendL and CL code. Emacs/Slime includes a Read-Eval-Print-Loop (REPL), which is an interactive, editable command prompt connected to a live GendL session (which itself is hosted in a running CL process). You will find that the REPL proves useful for testing and debugging code as you are writing it. Emacs also boasts a wide range of open-source plugins for customization and automation, including plugins for the emerging AI coding assistants such as Github Copilot.


Hyperlinked documentation for the objects, macros, functions, and global parameters provided with GendL is available through any web browser using YADD, a documentation generator built using... GendL. Assuming you have a running session which is using port 9000 for its webserver listener, then reference documentation for the developer will be accessible at [http://localhost:9000/yadd](http://localhost:9000/yadd). YADD may also be used to document your own user-defined objects, macros, functions, and global parameters. The resulting documentation available on the main YADD home page side by side with that for the built-in operators. In the picture on the right, you can see documentation links for built-in GendL packages such as CL-LITE, GENDL, GEOM-BASE, GEYSR, GWL and YADD, as well as user-defined packages such as PURSUIT-ANALYSIS, WEB-PARTS, and WIND-TUNNEL. From time to time, supplemental documentation may be published at [the Genworks Website]({target="_new"}.


As code is developed it may be evaluated in the CL Read-Eval-Print-Loop (REPL). Additionally, GendL provides a model and object browser called Geysr. This is a web-based UI which allows objects to be instantiated, navigated and inspected. Assuming you have a running session which is using port 9000 for its webserver listener, then Geysr will be available at [http://localhost:9000/geysr](http://localhost:9000/geysr). Geysr is also integrated with the REPL. By invoking Geysr's "Set Self!" action on any object in the object instance tree displayed Geysr, that object will become bound to a global variable `self`, allowing you to work with that object (including access to its ancestor and descendant instances). As with YADD, Geysr is also built using GendL itself.