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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 (?"hello")
  • 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 ^ (power) operator is implemented using floating point, which is inelegant and a potential performance issue, and 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.