z8lua

This is a fork of Lua that implements the PICO-8 dialect and adds useful features for emulator implementations.

Branches

The main zepto8 branch is a composite branch built from several feature branches. Please try to submit patches and PRs against the corresponding feature branch instead of zepto8.

There are three main feature branches:

• pico8: this is a “clean” branch that only implements the PICO-8 syntax and type system, with no extra fancy features; a good start if you’re writing your own emulator.
• eris: a branch imported from the eris persistence patch with bug fixes and improvements (my pull requests have received little attention so far); this library provides serialisable snapshots of the Lua state (quite useful for emulators).
• oua: experimental branch allowing to switch on-the-fly to zero-based indices in Lua, using the base(0) function and back with base(1). I call this the Oua language.

PICO-8 features

• short if syntax (on one line)
• short print syntax (? at the beginning of a line)
• compound assignment operators: += /= etc.
• C style not equal operator: !=
• C++ style comments with //
• fixed-point arithmetic with overflows, infinity etc.
• the PICO-8 math library (shr, atan2, flr etc.)
• binary literals: 0b1001001.10010
• works in Windows, Linux, OS X, and many embedded systems

Limitations

• Lua functions that rely on the PICO-8 state, particularly the VM memory, are beyond the scope of this software; for a more complete PICO-8 implementation, see the zepto8 emulator which is based on z8lua. The only exceptions are the @, % and $ operators (see next section).
• the sqrt, sin, cos and atan2 functions are implemented using floating point, which is inelegant and a potential performance issue, but which also means the results are not bit-by-bit equivalent to the original PICO-8.

API extensions

LUA_API void lua_setpico8memory (lua_State *L, unsigned char const *p);

Provide the Lua VM with a 64-KiB address space for use with the @, % and $ operators (shorthands for peek, peek2, and peek4). Otherwise these operators will always return 0.