Module:fun

fun stands for "functional", but also functional programming can be fun. This library contains some typical metafunctions for functional programming, such as map, some, all, curry, as well as others.

Functions that take an array as their second argument are available as methods in the arrays created by Module:array, with the arguments reversed so that they can be called as methods.

It was started in a user sandbox (Module:User:Erutuon/functional). It is not to be confused with Lua Fun (of which there is a version at Module:User:Erutuon/luafun), even though some functions are similar.

The functions that take a table as their second argument will treat the table as an array if t[1] is not nil, and use ipairs. Otherwise, they will treat it as a hashmap, using pairs.

function map(func, iterable)

Perform a function func on every element in iterable and return the resulting table. iterable may be a table or a string. If a table, the function operates on every element in the array portion of the table; if a string, the function operates on every UTF-8 character in the string. The function func has the following signature: func(member, i, iterable). That is, the table element or UTF-8 character is first, then the index of this element, and then the iterable value (table or string).

function mapIter(func, iterator, iterable, initial_value)

Create a new array from the results of performing a function on the values returned by an iterator. Can be used in combination with sortedPairs in Module:table. func has the same signature described above. Not very useful with gmatch; func would have a nil first argument, because the single value returned from the iterator would be supplied as the second argument to func.

mapIter(
    function(parameter_value, parameter_name)
        return { parameter_name, parameter_value }
    end,
    sortedPairs(frame.args))
--> returns a sorted array of arrays containing parameter names and values

---

local export = {}

local ustring = mw.ustring
local libraryUtil = require "libraryUtil"
local checkType = libraryUtil.checkType
local checkTypeMulti = libraryUtil.checkTypeMulti

local iterableTypes = { "table", "string" }

local function _check(funcName, expectType)
	if type(expectType) == "string" then
		return function(argIndex, arg, nilOk)
			return checkType(funcName, argIndex, arg, expectType, nilOk)
		end
	else
		return function(argIndex, arg, expectType, nilOk)
			if type(expectType) == "table" then
				if not (nilOk and arg == nil) then
					return checkTypeMulti(funcName, argIndex, arg, expectType)
				end
			else
				return checkType(funcName, argIndex, arg, expectType, nilOk)
			end
		end
	end
end

-- Iterate over UTF-8-encoded codepoints in string.
local function iterString(str)
	local iter = string.gmatch(str, "[%z\1-\127\194-\244][\128-\191]*")
	local i = 0
	local function iterator()
		i = i + 1
		local char = iter()
		if char then
			return i, char
		end
	end
	
	return iterator
end

function export.chain(func1, func2, ...)
	return func1(func2(...))
end

--	map(function(number) return number ^ 2 end,
--		{ 1, 2, 3 })									--> { 1, 4, 9 }
--	map(function (char) return string.char(string.byte(char) - 0x20) end,
--		"abc")											--> { "A", "B", "C" }
function export.map(func, iterable, isArray)
	local check = _check 'map'
	check(1, func, "function")
	check(2, iterable, iterableTypes)
	
	local array = {}
	local iterator = type(iterable) == "string" and iterString
		or (isArray or iterable[1] ~= nil) and ipairs or pairs
	for i_or_k, val in iterator(iterable) do
		array[i_or_k] = func(val, i_or_k, iterable)
	end
	return array
end

function export.mapIter(func, iter, iterable, initVal)
	local check = _check 'mapIter'
	check(1, func, "function")
	check(2, iter, "function")
	check(3, iterable, iterableTypes, true)
	
	-- initVal could be anything
	
	local array = {}
	local i = 0
	for x, y in iter, iterable, initVal do
		i = i + 1
		array[i] = func(y, x, iterable)
	end
	return array
end

function export.forEach(func, iterable, isArray)
	local check = _check 'forEach'
	check(1, func, "function")
	check(2, iterable, iterableTypes)
	
	local iterator = type(iterable) == "string" and iterString
		or (isArray or iterable[1] ~= nil) and ipairs or pairs
	for i_or_k, val in iterator(iterable) do
		func(val, i_or_k, iterable)
	end
	return nil
end

-------------------------------------------------
-- From [[http://lua-users.org/wiki/CurriedLua]].
-- reverse(...) : take some tuple and return a tuple of elements in reverse order
--
-- e.g. "reverse(1,2,3)" returns 3,2,1
local function reverse(...)
	-- reverse args by building a function to do it, similar to the unpack() example
	local function reverseHelper(acc, v, ...)
		if select('#', ...) == 0 then
			return v, acc()
		else
			return reverseHelper(function() return v, acc() end, ...)
		end
	end
	
	-- initial acc is the end of the list
	return reverseHelper(function() return end, ...)
end

function export.curry(func, numArgs)
	-- currying 2-argument functions seems to be the most popular application
	numArgs = numArgs or 2
	
	-- no sense currying for 1 arg or less
	if numArgs <= 1 then return func end
	
	-- helper takes an argTrace function, and number of arguments remaining to be applied
	local function curryHelper(argTrace, n)
		if n == 0 then
			-- kick off argTrace, reverse argument list, and call the original function
			return func(reverse(argTrace()))
		else
			-- "push" argument (by building a wrapper function) and decrement n
			return function(onearg)
				return curryHelper(function() return onearg, argTrace() end, n - 1)
			end
		end
	end
	
	-- push the terminal case of argTrace into the function first
	return curryHelper(function() return end, numArgs)
end

-------------------------------------------------

--	some(function(val) return val % 2 == 0 end,
--		{ 2, 3, 5, 7, 11 })						--> true
function export.some(func, t, isArray)
	if isArray or t[1] ~= nil then -- array
		for i, v in ipairs(t) do
			if func(v, i, t) then
				return true
			end
		end
	else
		for k, v in pairs(t) do
			if func(v, k, t) then
				return true
			end
		end
	end
	return false
end

--	all(function(val) return val % 2 == 0 end,
--		{ 2, 4, 8, 10, 12 })					--> true
function export.all(func, t, isArray)
	if isArray or t[1] ~= nil then -- array
		for i, v in ipairs(t) do
			if not func(v, i, t) then
				return false
			end
		end
	else
		for k, v in pairs(t) do
			if not func(v, k, t) then
				return false
			end
		end
	end
	return true
end

function export.filter(func, t, isArray)
	local new_t = {}
	if isArray or t[1] ~= nil then -- array
		local new_i = 0
		for i, v in ipairs(t) do
			if func(v, i, t) then
				new_i = new_i + 1
				new_t[new_i] = v
			end
		end
	else
		for k, v in pairs(t) do
			if func(v, k, t) then
				new_t[k] = v -- or create array?
			end
		end
	end
	return new_t
end


-------------------------------
-- Fancy stuff
local function capture(...)
	local vals = { ... }
	return function()
		return unpack(vals)
	end
end

-- Log input and output of function.
-- Receives a function and returns a modified form of that function.
function export.logReturnValues(func, prefix)
	return function(...)
		local inputValues = capture(...)
		local returnValues = capture(func(...))
		if prefix then
			mw.log(prefix, inputValues())
			mw.log(returnValues())
		else
			mw.log(inputValues())
			mw.log(returnValues())
		end
		return returnValues()
	end
end

export.log = export.logReturnValues

-- Convenience function to make all functions in a table log their input and output.
function export.logAll(t)
	for k, v in pairs(t) do
		if type(v) == "function" then
			t[k] = export.logReturnValues(v, tostring(k))
		end
	end
	return t
end

----- M E M O I Z A T I O N-----
-- metamethod that does the work
-- Currently supports one argument and one return value.
local func_key = {}
local function callMethod(self, x)
	local output = self[x]
	if not output then
		output = self[func_key](x)
		self[x] = output
	end
	return output
end

-- shared metatable
local mt = { __call = callMethod }

-- Create callable table.
function export.memoize(func)
	return setmetatable({ [func_key] = func }, mt)
end

-------------------------------

return export