epatrizio / ola

OCaml Lua Interpreter

Hi there 👋

tl;dr

• 💻 R&D software engineer
• 💽 Computer Scientist, work in progress ;)
• ➿ Programming languages design enthusiast
• 🌍 Need for open source
• 🌻 Convinced by the minimalist philosophy
• 🤔 Discovering low tech computing approach
• 🐫 OCaml
• 🕸 WebAssembly (wasm)
• 🐘 PHP
• 🌔 Lua
• 📖 Life long learner

current status

OCamlPro company

I contribute to the OCamlPro owi 🐌 project (OCaml WebAssembly toolchain : concrete and symbolic interpretation), part of a research project on OCaml to Wasm compilation.

Side project

ola (OCaml Lua experiments) is a personal experimental project. First step, ola is a Lua language interpreter written in OCaml.
My objective is to obtain a deeper understanding of dynamic languages design.

ola's Issues

Table support

For now, the length operator # implementation for table calls Table.len function

ola/src/interpret.ml

Line 364 in 93425d7

(Vnumber (Ninteger (Table.len t)), env)

This operator must return the border of the table, note len. It's not exactly the same.
https://www.lua.org/manual/5.4/manual.html#3.4.7

Improve goto label implementation

Complete code checks before interpretation :

• label init : label already exists
• goto : label not exists
• ...

Improve pretty printer

OCaml Format module (Boxes ...)
https://v2.ocaml.org/api/Format.html
https://ocaml.org/docs/formatting-text

Bug recursive function

Check example Fibonacci -- 2: Recursive version with memoization
https://github.com/epatrizio/ola/blob/main/examples/fibonacci.lua

Memoization does not work:

local fib = fibo2(n-1) + fibo2(n-2)
mem[n] = fib

the trouble seems to be at the double recursive call level ...

Bug return statement

3.3.4 – Control Structures (official documentation)
https://www.lua.org/manual/5.4/manual.html#3.3.4

The return statement can only be written as the last statement of a block. If it is necessary to return in the middle of a block, then an explicit inner block can be used, as in the idiom do return end, because now return is the last statement in its (inner) block.

--
Actually, when return isn't at the end of the block, the stop is still made at this point.

Improve REPL

For now, REPL supports only statement :
expressions produce syntax errors.

Bug closure concept implementation

Here is the classic example :

function add(x)
  return function(n)
    return x + n
  end
end
local add2 = add(2)
print(add2)          -- Type = add2 is a function
print(add2(40))   -- Result expected = 42

error launched : attempt to perform arithmetic on a nil value
x is not defined. x should be equal to 2 !

https://en.wikipedia.org/wiki/Closure_(computer_programming)

Improve return statement

Many questions came up during return implementation about adding some syntax strong controls.
for example, return options only in a specific context (in a function blocks for example)

Where to implement this stuff : in menhir parser.mly ?
What is the best practice ?

béta version :
67691ab

Spec :
https://www.lua.org/manual/5.4/manual.html#3.3.4

Bug comment

A comment on the last line causes an error :
Fatal error: exception Assert_failure("src/lexer.ml", 155, 9)

Bug function call with single string arg (syntactic sugar)

doc §3.4.10 https://www.lua.org/manual/5.4/manual.html#3.4.10
A call of the form f'string' (or f"string" or f[[string]]) is syntactic sugar for f('string')

6c89c2b

Syntax error lines 90 & 92 in function.lua test
https://github.com/epatrizio/ola/blob/main/test/function.lua

Bug variadic function

Parsing error with function signature like function f(a, ...)
function f(...) is ok !

Bug table col access by name

Ex. in ./test/table.lua table1."key3" = "val3" statement causes an error
(syntactic error - parsing, lexing, other ?)

Check b901d0d

Migrate to cmdliner

Migrate OCaml Arg module (https://v2.ocaml.org/api/Arg.html) to Cmdliner (https://github.com/dbuenzli/cmdliner)