provide dir and dir2 functions for listing table keys

Both functions don't expand tables used as keys/values.

`dir(table)` will list `key = value` pairs, but non-recursively.
`dir2(table)` will only list the keys.

These functions return nothing and are to be used only interactively.

dump.lua

@@ -119,4 +119,35 @@ local function repl_dump(o, indent, nested, level)
     return "{"..table.concat(ret, ", ").."}"
 end
 
-return repl_dump
+
+local function dump_dir(o)
+    -- dump only top-level key = value pairs
+    local t = type(o)
+    if t ~= "table" then
+        return basic_dump(o)
+    end
+
+    local ret = {}
+    local dumped_indexes = {}
+    for i, v in ipairs(o) do
+        ret[#ret + 1] = string.format("[%s] = %s", i, basic_dump(v))
+        dumped_indexes[i] = true
+    end
+    for k, v in pairs(o) do
+        if not dumped_indexes[k] then
+            if type(k) ~= "string" or not is_valid_identifier(k) then
+                k = "["..basic_dump(k).."]"
+            end
+            v = basic_dump(v)
+            ret[#ret + 1] = k.." = "..v
+        end
+    end
+    return "{\n "..table.concat(ret, ",\n ").."\n}"
+end
+
+local dump_funcs = {
+    repl_dump = repl_dump,
+    dump_dir = dump_dir,
+}
+
+return dump_funcs

init.lua

@@ -2,7 +2,9 @@ local MODNAME = core.get_current_modname()
 local MODPATH = core.get_modpath(MODNAME)
 
 local util = dofile(MODPATH .. DIR_DELIM .. "util.lua")
-local repl_dump = dofile(MODPATH .. DIR_DELIM .. "dump.lua")
+local dump_funcs = dofile(MODPATH .. DIR_DELIM .. "dump.lua")
+local repl_dump = dump_funcs.repl_dump
+local dump_dir = dump_funcs.dump_dir
 
 local api = {}
 _G[MODNAME] = api
@@ -85,11 +87,14 @@ local function create_shared_environment(player_name)
                 end
                 core.chat_send_player(player_name, msg)
             end,
-            dir = function(t)
-                -- collect all keys of the table
-                if type(t) == "table" then
+            dir = function(o)
+                core.chat_send_player(player_name, dump_dir(o))
+            end,
+            dir2 = function(o)
+                -- collect all keys of the table, no values
+                if type(o) == "table" then
                     local keys = {}
-                    for k, _ in pairs(t) do
+                    for k, _ in pairs(o) do
                         local key = k
                         local t = type(key)
                         if t == "string" then