Function module 

pub fn module(lua: &Lua) -> Result<Table>

Register the flow module table with Lua.

Exposes:

• flow.version (= string): crate version
• flow.eval(node_table, ctx_table, dispatcher_fn, externs_table?) -> result_table: Lua-side entry to evaluate a flow.ir BluePrint with a Lua dispatcher fn. Optional 4th arg is a table of pure Lua functions resolved by call_extern Expr (canonical opts.externs parity).

Lua usage

local flow = require("flow")  -- or set via lua.globals():set("flow", module(lua))

local node = {
  kind = "step",
  ref = "uppercase",
  ["in"] = { op = "path", at = "$.input" },
  out = { op = "path", at = "$.output" },
}

local function dispatcher(ref, input)
  if ref == "uppercase" then
    return string.upper(input)
  end
end

local result = flow.eval(node, { input = "hello" }, dispatcher)
assert(result.output == "HELLO")

-- call_extern: whitelist pure Lua fns via the externs table
local node2 = {
  kind = "assign",
  at = { op = "path", at = "$.root" },
  value = { op = "call_extern", ref = "math.sqrt",
            args = { { op = "path", at = "$.n" } } },
}
local result2 = flow.eval(node2, { n = 9 }, dispatcher,
                          { ["math.sqrt"] = math.sqrt })
assert(result2.root == 3)