The NEX Book

NEX is a small interpreted programming language for learning the foundations of programming. It emphasizes explicit types, clear control flow, and predictable rules, so new programmers can focus on how values, variables, functions, and scope work together.

NEX is deliberately compact. It includes the core building blocks of programming such as integers, strings, booleans, variables, expressions, functions, and loops, but leaves out larger abstraction systems such as classes and first-class functions. That keeps attention on the basic patterns of programming and on how simple constructs can be combined to solve larger problems.

This book explains NEX as a language for learning. It aims to show not only what programs can be written, but also why they behave the way they do.

Here is a small complete program:

int x = 0;

while (x < 5) {
    print(x);
    x++;
}

Installation

Install NEX locally in editable mode:

python -m pip install -e .

Once published, NEX can also be installed from PyPI:

python -m pip install nex-lang

This installs the nexlang command-line runner. For example:

nexlang examples/hello.nex

The runner can also show intermediate views and execution timings:

nexlang tokens examples/hello.nex
nexlang ast examples/hello.nex
nexlang --times examples/hello.nex
nexlang run --times --color examples/hello.nex

Use --times to print a timing summary for lexing, parsing, interpretation, and total execution. Add --color or -c if you want that timing table highlighted with colors.

The reference chapters describe the language as it exists today. They focus on source-level behavior rather than interpreter internals, but they are written with implementation-minded readers in mind. When the implementation and the book disagree, that is a bug to fix rather than a reason to guess.

When writing documentation, fenced ```nex blocks are highlighted automatically. Inline snippets can also be highlighted, but inline Markdown backticks do not carry language information. For inline NEX syntax, use raw HTML such as <code class=“language-nex”>arr.length()</code>.

The current implementation also provides structured diagnostics for lexing, parsing, and runtime failures. These diagnostics report the phase together with source line and column information when available, which makes NEX a better tool both for writing small programs and for studying how a language reports errors in a disciplined way.