Generate Amulet binding

gen-aml.lua

--[[
ᐅ cat another.lua
return { a = 1, b = function() end }
ᐅ lua5.3 dump.lua another
external val another_b : unit -> 'a = "require(\"another\").b"
external val another_a : float = "require(\"another\").a"
(* external val another : table = "require(\"another\")" *)
]]
local module = ... or error("gen-aml.lua MODULE")

local function print_binding(name, path, val)
  local ty = type(val)
  local aml_ty
  if ty == "number" then
    aml_ty = "float"
  elseif ty == "boolean" then
    aml_ty = "bool"
  elseif ty == "table" then
    for k, v in pairs(val) do
      if type(k) == "string" and k:match("^%a[%w_]*$") then
        print_binding(name .. "_" .. k, path .. "." .. k, v)
      end
    end
  elseif ty == "function" then
    local info = debug.getinfo(val, "Su")
    if info and info.what == "Lua" then
      if info.nparams == 0 then
        aml_ty = "unit -> 'a"
      else
        aml_ty = ""
        for i = 1, info.nparams do
          aml_ty = aml_ty .. ("'%c -> "):format(96 + i)
        end
        aml_ty = aml_ty .. ("'%c"):format(96 + i)
      end
    end
  end

  if not aml_ty then io.write("(* ") end
  io.write(("external val %s : %s = %q"):format(name, aml_ty or ty, path))
  if not aml_ty then io.write(" *)") end
  io.write("\n")
end

print_binding(module, ("require(%q)"):format(module), require(module))