Values and types

KCL defines the following types and keywords the language.

All these types can be nested in various forms where nesting applies. Like arrays can hold objects and vice versa.

Constant declaration

Constants are defined with a name and a value, like so:

Currently you cannot redeclare a constant.

Objects

An object is defined with {} braces. Here is an example object:

To get the property of an object, you can call myObj.a, which in the above example returns 0.

ImportedGeometry

Using import you can import geometry defined using other CAD software. In KCL, these objects have type ImportedGeometry and can mostly be treated like any other solid (they can be rotated, scaled, etc.), although there is no access to their internal components. See the modules and imports docs for more detail on importing geometry.

Tags

Tags are used to give a name (tag) to a specific path.

Tag declarations - TagDecl

The syntax for declaring a tag is $myTag. Tags are used for bodies (such as extrude cap faces). For sketches, reference segment names directly.

Example: Referencing sketch segments and tagging cap faces

In this example, you reference sketch segments from sketch blocks by their names, using dot notation on the sketch (e.g. sketch001.line4). Sketches from KCL 1.0 (using startSketchOn()) and regions are scoped to tags, as in region001.tags.line4. Tags (using $) are only needed for cap faces or other body features.

When a function requires declaring a new tag (using the $ syntax), the argument has type TagDecl.

Tag identifiers

A tag created using a tag declarator can be used by writing its name without the $, e.g., myTag. Where necessary to disambiguate from tag declarations, we call these tag identifiers.

In the example above we use the tag identifier capEnd001 to get the edge in common using getCommonEdge(capEnd001).

Tags can identify an edge or face of a solid. Functions that take a tag identifier as an argument will use either TaggedEdge (for the edge of a solid) or TaggedFace.

START and END vs. body.faces

START and END are special tags for identifying the starting and ending faces of an extruded solid.

Using START and END can be convenient sometimes, but they are generally discouraged since they're ambiguous. It's not clear what face is being referred to without also specifying the body.

When you tag a face in an extrusion, it becomes one of that body's named faces. In the example above, extrude001.faces.capEnd001 refers to the end-cap face.

This is also useful when you create the body in a function and need to refer to one of its faces in the calling scope. You can simply return the body, and callers can access all of the body's named faces.

Tag Scope

Tags are scoped globally if declared in the root context. For bodies, you can use the tag anywhere in the file. For sketches, always use the segment name directly.

For backward compatibility reasons, tags may leak outside of function scopes and be updated (i.e. re-bound to the face of a different body), which can be confusing about which geometry you're trying to refer to.

For this reason, it's strongly preferred to use dot notation on the body, as in extrude001.faces.capEnd001 for an end-cap face or region001.tags.line4 for a wall face.

If you find any issues using any of the above expressions or syntax, please file an issue with the ast label on the modeling-app repo.