Introduction

Nucleus is a language for programs that must fit inside a small Z80 system. The Z80 is an 8-bit processor used in early personal computers and in small machines built today. Its limited memory makes the cost of every program data structure matter.

Nucleus has three scalar types with fixed ranges. Arrays have fixed lengths, strings have fixed capacities and records have fixed fields. The compiler checks those rules before it emits machine code, then inserts runtime checks for values known only while the program runs.

The compiler itself is a Z80 program. It reads Nucleus source in order and emits Z80 machine code directly. The command-line tool and Debug80 both run that same compiler.

The intended reader

This book assumes that you have seen variables, expressions, conditions and loops in another language. Every Nucleus construct is introduced before a program depends on it. Z80 instructions, registers and calling conventions are outside the required starting knowledge because Nucleus source does not expose them.

The examples use small integer problems, byte-oriented input and fixed data structures. These suit monitors, utilities, controllers, data loggers and games. Each complete listing is available beside its chapter as runnable source.

From source to a program

You write Nucleus source in .nu files. The compiler reads those files in the order supplied by the build and produces Z80 machine code. The shortest route looks like this:

Nucleus source → Nucleus compiler → NOBJ

NOBJ is the compiler's output file. It contains the generated program and the information needed to place that program in memory. The first chapter builds one with the compiler's built-in settings. Later chapters add the description of a particular machine needed to load, run and debug a program there.

Two kinds of unsuccessful operation recur throughout the book. A routine can report an expected error code for its caller to propagate or handle. A safety trap, such as an out-of-bounds index, ends source execution. Nucleus keeps that distinction visible in the program.

The book's method

Chapters begin with a programming problem, trace the relevant values, state the governing rules and test the boundary cases. The first program calculates a price and leaves the result in program storage. Later programs need decisions, loops, fixed data, routine calls and recoverable failure.

The complete rule set lives in the Nucleus 0.1 Language Specification. Links at the end of each chapter point to the sections that govern its examples.