Ravi Programming Language
Ravi is a dialect of Lua with limited optional
static typing and features MIR
powered JIT compilers. The name Ravi comes from the Sanskrit word for
the Sun. Interestingly a precursor to Lua was
Sol which had support for static
types; Sol means the Sun in Portugese.
Lua is perfect as a small embeddable dynamic language so why a
derivative? Ravi extends Lua with static typing for improved performance
when JIT compilation is enabled. However, the static typing is optional
and therefore Lua programs are also valid Ravi programs.
There are other attempts to add static typing to Lua - e.g. Typed
Lua but these efforts are mostly
about adding static type checks in the language while leaving the VM
unmodified. The Typed Lua effort is very similar to the approach taken
programming in the large - the code is eventually translated to standard
Lua and executed in the unmodified Lua VM.
My motivation is somewhat different - I want to enhance the VM to
support more efficient operations when types are known. Type information
can be exploited by JIT compilation technology to improve performance.
At the same time, I want to keep the language safe and therefore usable
by non-expert programmers.
Of course there is the fantastic LuaJIT
implementation. Ravi has a different goal compared to LuaJIT. Ravi
prioritizes ease of maintenance and support, language safety, and
compatibility with Lua 5.3, over maximum performance. For more detailed
comparison please refer to the documentation links below.
Lua 5.4 Position Statement
Lua 5.4 relationship to Ravi is as follows:
- Generational GC - back-ported to Ravi.
- New random number generator - back-ported to Ravi.
- Multiple user values can be associated with userdata - under
<const> variables - not planned.
<close> variables - Ravi has
'defer' statement which is the
better option in my opinion, hence no plans to support
- Interpreter performance improvements - these are beneficial to Lua
interpreter but not to the JIT backends, hence not much point in
- Table implementation changes - under consideration.
- String to number coercion is now part of string library metamethods
- utf8 library accepts codepoints up to 2^31 - back-ported to Ravi.
- Removal of compatibility layers for 5.1, and 5.2 - not implemented
as Ravi continues to provide these layers as per Lua 5.3.
Compatibility with Lua 5.3
Ravi should be able to run all Lua 5.3 programs in interpreted mode, but
following should be noted:
- Ravi supports optional typing and enhanced types such as arrays (see
the documentation). Programs using these features cannot be run by
standard Lua. However all types in Ravi can be passed to Lua
functions; operations on Ravi arrays within Lua code will be subject
to restrictions as described in the section above on arrays.
- Values crossing from Lua to Ravi will be subjected to typechecks
should these values be assigned to typed variables.
- Upvalues cannot subvert the static typing of local variables (issue
#26) when types are annotated.
- Certain Lua limits are reduced due to changed byte code structure.
These are described below.
- Ravi uses an extended bytecode which means it is not compatible with
Lua 5.x bytecode.
- Ravi incorporates the new Generational GC from Lua 5.4, hence the GC
interface has changed.
Limit name Lua value Ravi value
MAXUPVAL 255 125
LUAI_MAXCCALLS 200 125
MAXREGS 255 125
MAXVARS 200 125
MAXARGLINE 250 120
When JIT compilation is enabled there are following additional
- Ravi will only execute JITed code from the main Lua thread; any
secondary threads (coroutines) execute in interpreter mode.
- In JITed code tailcalls are implemented as regular calls so unlike
the interpreter VM which supports infinite tail recursion JIT
compiled code only supports tail recursion to a depth of about 110
- Debug api and hooks are not supported in JIT mode
- Embedded C compiler using dmrC project (C JIT compiler) (now
- Additional type-annotations
- New language feature - defer statement
- New JIT backend MIR.
- 2021 (Plan)
- Integrated AOT and JIT compilation support
- Ravi 1.0 release