String Builder is now an actual object, and can now be called to append.

pretty.lua

@@ -353,12 +353,10 @@ function format_table (t, options, depth, l)
 
     if table_info.type == TABLE_TYPE.EMPTY then
         -- Empty Map
-        l[#l+1] = '{}'
-        return;
+        return l '{}'
     elseif depth >= options.max_depth or already_visited then
         -- Already visited or above max depth
-        l[#l+1] = '{...}'
-        return;
+        return l '{...}'
     end
 
     -- Get key-value pairs, and possibly fill holes.
@@ -475,6 +473,17 @@ function format_value (value, _, depth, l)
 end
 
 --------------------------------------------------------------------------------
+-- StringBuilder
+
+local StringBuilder = {}
+      StringBuilder.__index = StringBuilder
+      StringBuilder.__call  = function (l, s) l[#l+1] = s end
+setmetatable(StringBuilder, {
+    __call = function() return setmetatable({}, StringBuilder) end
+})
+
+--------------------------------------------------------------------------------
+
 
 local DEBUG_OPTIONS = { _all_function_info = true }
 
@@ -491,6 +500,7 @@ local KNOWN_OPTIONS = {
 }
 
 local function ensure_that_all_options_are_known (options)
+    assert(type(options) == 'table')
     for option_name, option_value in pairs(options) do
         if not KNOWN_OPTIONS[option_name] then
             error(('[pretty]: Unknown option: %s. Was given value %s (%s)'):format(option_name, option_value, type(option_value)), 2)
@@ -501,12 +511,19 @@ local function ensure_that_all_options_are_known (options)
 end
 
 local function pretty_format (value, options)
-    local l = { visited = { next_mark = 1 } }
-    l.options = options or {}
-    l.options.max_depth = l.options.max_depth or math.huge
-    l.options.indent    = l.options.indent    or '\t'
-    ensure_that_all_options_are_known(l.options)
-    l.info = (type(value) == 'table') and analyze_structure(value) or {}
+    -- Error checking
+    options = options or {}
+    options.max_depth = options.max_depth or math.huge
+    options.indent    = options.indent    or '\t'
+    ensure_that_all_options_are_known(options)
+
+    -- Setup StringBuilder
+    local l = StringBuilder()
+          l.visited = { next_mark = 1 }
+          l.options = options
+          l.info = (type(value) == 'table') and analyze_structure(value) or {}
+
+    -- Format value.
     format_value(value, nil, 0, l)
 
     -- If any alignment info still exists, ignore it