add gs

RCCService2021/ExtraContent/LuaPackages/AppTempCommon/Common/Functional.lua

@@ -0,0 +1,131 @@
+--[[
+	Provides an implementation of functional programming primitives.
+]]
+
+local Functional = {}
+
+--[[
+	Create a copy of a list with only values for which `callback` returns true
+]]
+function Functional.Filter(list, callback)
+	local new = {}
+
+	for key = 1, #list do
+		local value = list[key]
+		if callback(value, key) then
+			table.insert(new, value)
+		end
+	end
+
+	return new
+end
+
+--[[
+	Create a copy of a list where each value is transformed by `callback`
+]]
+function Functional.Map(list, callback)
+	local new = {}
+
+	for key = 1, #list do
+		new[key] = callback(list[key], key)
+	end
+
+	return new
+end
+
+--[[
+	Identical to Map, except that the result will be reversed.
+]]
+function Functional.MapReverse(list, callback)
+	local new = {}
+
+	for key = #list, 1, -1 do
+		new[key] = callback(list[key], key)
+	end
+
+	return new
+end
+
+--[[
+	Create a copy of a list doing a combination filter and map.
+
+	If callback returns nil for any item, it is considered filtered from the
+	list. Any other value is considered the result of the 'map' operation.
+]]
+function Functional.FilterMap(list, callback)
+	local new = {}
+
+	for key = 1, #list do
+		local value = list[key]
+		local result = callback(value, key)
+
+		if result ~= nil then
+			table.insert(new, result)
+		end
+	end
+
+	return new
+end
+
+--[[
+	Performs a left-fold of the list with the given initial value and callback.
+]]
+function Functional.Fold(list, initial, callback)
+	local accum = initial
+
+	for key = 1, #list do
+		accum = callback(accum, list[key], key)
+	end
+
+	return accum
+end
+
+--[[
+	Performs a fold over the entries in the given dictionary.
+]]
+function Functional.FoldDictionary(dictionary, initial, callback)
+	local accum = initial
+
+	for key, value in pairs(dictionary) do
+		accum = callback(accum, key, value)
+	end
+
+	return accum
+end
+
+--[[
+	Returns a list that contains at most `count` values from the given list.
+]]
+function Functional.Take(list, count, startingIndex)
+	startingIndex = startingIndex or 1
+
+	local maxIndex = count + (startingIndex - 1)
+	if maxIndex > #list then
+		maxIndex = #list
+	end
+
+	local new = {}
+
+	for i = startingIndex, maxIndex do
+		local value = list[i]
+		local newIndex = i - (startingIndex - 1)
+		new[newIndex] = value
+	end
+
+	return new
+end
+
+--[[
+	If the list contains the sought-after element, return its index, or nil otherwise.
+]]
+function Functional.Find(list, value)
+	for index, element in ipairs(list) do
+		if element == value then
+			return index
+		end
+	end
+
+	return nil
+end
+
+return Functional