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Preprocessor

The preprocessor runs before compilation and handles C-like directives over the raw source text. It can be disabled entirely with the --disable-preprocessor CLI flag.

Directives

#define NAME [value]

Define a preprocessor constant. If value is omitted, the symbol is defined but has no substitution value (useful for #ifdef guards).

The value can be an integer literal, float, string, or a constant expression.

#define MAX_SIZE 1024
#define PI 3.14159
#define GREETING "hello"
#define FEATURE_FLAG

#include "file.nyx"

Include another source file. The preprocessor searches for the file in the following locations, in order:

  1. The current working directory
  2. The directory of the source file containing the #include
  3. Any directories passed with the -i / --include CLI flag
  4. The directory specified by the NYX_STDLIB_PATH environment variable
#include "stdlib.nyx"
#include "mylib.nyx"

#ifdef / #ifndef ... #else ... #endif

Conditional compilation. Code between the directives is included or excluded based on whether a symbol is defined.

#ifdef __LINUX__
    mov q0, 1
#else
    mov q0, 2
#endif

#ifndef DEBUG
    ; release-mode code
#endif

#macro NAME ($param1, $param2, ...) ... #endm

Define a multi-line macro with parameters. Parameters are prefixed with $ in both the declaration and the body. When the macro is invoked, the body is expanded with actual arguments substituted in place of the parameters.

#macro write ($fd, $addr, $len)
    mov q0, $fd
    mov q1, $addr
    mov q2, $len
    mov q15, SYS_WRITE
    syscall
#endm

A macro is invoked by name, with arguments separated by commas:

write STDOUT, message, 14

Macros can contain any valid statements — instructions, directives, labels, etc.

#error "message"

Emit a compile-time error with the given message. Useful for guarding against unsupported configurations.

#ifndef __LINUX__
#error "This program only supports Linux"
#endif

Built-in Definitions

The preprocessor automatically defines platform-specific symbols based on the build target. These are available without any explicit #define.

Architecture:

Symbol Platform
__X86_64__ x86-64
__AARCH64__ AArch64 / ARM64
__RISCV64__ RISC-V 64-bit
__ARM__ ARM 32-bit
__WASM32__ WebAssembly 32-bit

Operating System:

Symbol Platform
__LINUX__ Linux
__MACOS__ macOS
__WINDOWS__ Windows
__FREEBSD__ FreeBSD

Expression Evaluation

The preprocessor can evaluate constant expressions in #define values. Supported operators:

Operator Description
+ - * / Arithmetic
| & ^ Bitwise OR, AND, XOR
- (unary) Negation
( ) Grouping 
#define PAGE_SIZE 4096
#define PAGE_MASK (PAGE_SIZE - 1)
#define FLAGS (0x01 | 0x04)

Include Guards

The standard pattern for preventing duplicate inclusion uses #ifndef / #define / #endif:

#ifndef MYLIB_NYX
#define MYLIB_NYX

; ... library content ...

#endif

Full Example

#include "stdlib.nyx"

#macro write ($fd, $addr, $len)
    mov q0, $fd
    mov q1, $addr
    mov q2, $len
    mov q15, SYS_WRITE
    syscall
#endm

.section text
_start:
    write STDOUT, message, 14
    hlt

.section data
message:
    db "Hello, world!\n", 0x00

Disabling the Preprocessor

Pass --disable-preprocessor to skip preprocessing entirely:

nyx build main.nyx --disable-preprocessor
nyx run main.nyx --disable-preprocessor

When disabled, no directives are processed and the source is passed directly to the lexer.