Creating a new snip% with Racket

Question

I am trying to create a new GUI element within DrRacket's text window, like picts or syntax objects. As far as I can tell, the most standard way of doing this is with a snip%.¹

Unfortunately, the documentation for creating new snips, while comprehensive, is a bit impenetrable and leaves some questions to be answered.

For starters, what is the difference between a snip% and a snip-class%? Why do these need to be separated out into two classes, rather than simply being combined into one class? Is it because multiple snips will use one snip class?

Second off, what is snip-reader<%>? Not only why does it need to be a separate class, but why is the module providing it supposed to be installed?² If it does need to be a new class, why can't it just be referred to directly. Why go through this whole process of constructing and then parsing a string of the form: "(lib ...)\n(lib ...)"?

I mean, there might now be any reason for this design, and it might just be a remnant of an old API. If so, has anyone thought of making a new more consistent API? Or if there is a reason for this design, can you please tell me what it is, as the docs don't seem to make that clear.

I mean, as of right now, I can copy/paste the sample given in the docs on creating a new snip. But I'm having a hard time understanding the design going on here, so I can use them properly.

_{¹I know there are other ways to do it, but I also want to have interactive buttons and whatnot.}

_{²I know it doesn't need to be installed as a library per se, but the documentation seems to strongly push you in that direction.}

Answer 1

Okay, I think I finally found the answer. Broadly speaking:

The snip% class includes the methods for drawing the snip, telling the editor how much space to reserve for the picture, and handling events such as mouse clicks.

Next, the snip-class% class is used for encoding and decoding snips. This must be a separate class because when saved to a file, the editor needs to encode what type of snip it is, and for obvious reasons it can't just put the literal snip% class in there. The value it stores in the file is the snip-class%'s 'class name'. This can be anything, and as long as the editor has the classname associated to a snip-class%, it can be loaded. Additionally, if it is of the form "(lib ...)" or "(lib ...) (lib ...)" Racket will just automatically load it into the list for you.

Nothing 'needs' to be installed per se, its just the easiest way to go about it. Otherwise you manually need to tell the editor how to handle the snip before actually loading the file.