Conditional Compilation

ifdef selectively includes or excludes code based on compile-time symbols.

Syntax

<?php
ifdef DEBUG {
    echo "debug mode\n";
} else {
    echo "release mode\n";
}

How it works

• Symbols set via --define CLI flags
• Resolved before include resolution and type checking
• Inactive branch completely removed from AST
• Inactive branches can reference files that don’t exist

Use cases

<?php
ifdef USE_SDL {
    extern "SDL2" {
        function SDL_Init(int $flags): int;
    }
    SDL_Init(0x20);
}

ifdef DEBUG {
    if ($hp < 0) {
        echo "BUG: negative HP!\n";
        exit(1);
    }
}

CLI usage

elephc --define DEBUG app.php
elephc --define DEBUG --define USE_SDL app.php

Nesting

<?php
ifdef PLATFORM_MAC {
    ifdef USE_METAL {
        echo "Metal renderer\n";
    } else {
        echo "OpenGL renderer\n";
    }
}

Constraints

• Symbols are simple names (no expressions, no ifndef, no #if)
• Symbols come only from --define flags
• ifdef is not PHP syntax

CLI flags reference

Flag	Description
--target TARGET	Compile for macos-aarch64, linux-aarch64, or linux-x86_64 instead of auto-detecting the host target
--heap-size=BYTES	Set heap buffer size (default 8MB, min 64KB)
--gc-stats	Print GC allocation/free statistics at exit
--heap-debug	Enable runtime heap verification (slow)
--emit-asm	Write the generated assembly and skip assemble/link
--check	Run the front-end pipeline without producing assembly or a binary
--timings	Print per-phase compiler timings to stderr
--source-map	Write a sidecar .map file next to generated assembly
--define SYMBOL	Define compile-time symbol for ifdef
--link LIB / -lLIB	Link an extra native library
--link-path DIR / -LDIR	Add an extra native library search path
--framework NAME	Link a macOS framework