Introduction
With Skate you write Scheme source in a text file, compile it under CP/M and run the resulting Z80 program. A calculation can print a total at the terminal. A larger program can process a list of purchases or respond to choices in an adventure. We begin with the calculation so you can complete the whole process before learning the language in detail.
Scheme expressions describe calculations and procedure calls. You can give a procedure a name, pass it to another procedure or return it as a result. Lists provide a way to collect related values and recursive procedures provide a way to process them. Later examples combine these ideas so you can change a calculation without rewriting the traversal of its data.
The small machine
Skate targets an eight-bit Z80 computer with a 64 KiB address space. CP/M occupies part of that space. We must fit the executable, runtime support, working storage and program data into the remainder. Skate implements a selected set of Scheme features within those limits.
Automatic memory management lets you allocate list elements and retain variables through closures without explicitly freeing each allocation. You still need enough memory for the data your program retains. We examine that cost after writing programs that create and process lists.
For this course you need a browser, a keyboard and a writable CP/M work disk with Skate and the text editor. Triptych runs the emulated computer in the browser. CP/M supplies the command prompt and file operations inside that computer. CP/M essentials introduces the commands used in the first lesson.
The language in this edition
The planned course uses Skate 0.5.5 as its starting baseline. It supports integer calculations, lists, procedures, closures and console character input. Floating-point arithmetic and several standard Scheme facilities remain outside that release. When you consult another Scheme book, check its examples against the version of Skate on your disk.
The first lesson uses facilities available in the older 0.5.1 browser starter. The chapters on later additions will require a matching teaching disk before publication. A working compiler in CP/M is sufficient for the opening lesson; knowledge of Z80 instructions is unnecessary.