Module:fun
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- The following documentation is located at Module:fun/documentation. [edit]
- Useful links: subpage list • links • transclusions • testcases • sandbox (diff)
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
funcon every element initerableand return the resulting table.iterablemay 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 functionfunchas 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
sortedPairsin Module:table.funchas the same signature described above. Not very useful withgmatch;funcwould have anilfirst argument, because the single value returned from the iterator would be supplied as the second argument tofunc. 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 format = string.format
local getmetatable = getmetatable
local gmatch = string.gmatch
local ipairs = ipairs
local is_callable -- defined as export.is_callable below
local pairs = pairs
local select = select
local tostring = tostring
local type = type
local unpack = unpack
local function _iterString(iter, i)
i = i + 1
local char = iter()
if char ~= nil then
return i, char
end
end
-- Iterate over UTF-8-encoded codepoints in string.
local function iterString(str)
return _iterString, gmatch(str, ".[\128-\191]*"), 0
end
--[==[
Return {true} if the input is a function or functor (a table which can be called like a function, because it has a {__call} metamethod).
]==]
function export.is_callable(f)
local f_type = type(f)
if f_type == "function" then
return true
elseif f_type ~= "table" then
return false
end
local mt = getmetatable(f)
-- __call metamethods have to be functions, not functors.
return mt and type(mt.__call) == "function" or false
end
is_callable = export.is_callable
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 array = {}
for k, v in (type(iterable) == "string" and iterString or (isArray or iterable[1] ~= nil) and ipairs or pairs)(iterable) do
array[k] = func(v, k, iterable)
end
return array
end
function export.mapIter(func, iter, iterable, initVal)
-- initVal could be anything
local array, i = {}, 0
for x, y in iter, iterable, initVal do
i = i + 1
array[i] = func(y, x, iterable)
end
return array
end
do
local function iter_tuples(tuples)
local i = tuples.i
if i > 1 then
i = i - 1
tuples.i = i
return unpack(tuples[i])
end
end
-- Takes an iterator function, and returns a new iterator that iterates in reverse, given the same arguments.
-- Note: changes to the state during iteration are not taken into account, since all the return values are calculated in advance.
function export.reverseIter(func)
return function(...)
-- Store all returned values as a list of tuples, then iterate in reverse over that list.
local tuples, i, iter, state, val1 = {}, 0, func(...)
while true do
i = i + 1
local vals = {iter(state, val1)}
-- Terminates if the first return value is nil, even if other values are non-nil.
val1 = vals[1]
if val1 == nil then
tuples.i = i
return iter_tuples, tuples
end
tuples[i] = vals
end
end
end
end
function export.forEach(func, iterable, isArray)
for k, v in (type(iterable) == "string" and iterString or (isArray or iterable[1] ~= nil) and ipairs or pairs)(iterable) do
func(v, 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)
for k, v in ((isArray or t[1] ~= nil) and ipairs or pairs)(t) do
if func(v, k, t) then
return true
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)
for k, v in ((isArray or t[1] ~= nil) and ipairs or pairs)(t) do
if not func(v, k, t) then
return false
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
function export.fold(func, t, accum)
for i, v in ipairs(t) do
accum = func(accum, v, i, t)
end
return accum
end
-------------------------------
-- Fancy stuff
local function capture(...)
local vals = { n = select('#', ...), ... }
return function()
return unpack(vals, 1, vals.n)
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-----
-- Memoizes a function or callable table.
-- Supports any number of arguments and return values.
-- If the optional parameter `simple` is set, then the memoizer will use a faster implementation, but this is only compatible with one argument and one return value. If `simple` is set, additional arguments will be accepted, but this should only be done if those arguments will always be the same.
do
-- Sentinels.
local args, nil_, neg_0, pos_nan, neg_nan
-- Since all possible inputs need to be memoized (including true, false and nil), the table of arguments is stored with the sentinel key `args`. In addition, certain values can't be used as table keys, so they require sentinels as well: e.g. f("foo", nil, "bar") would be memoized at f["foo"][nil_]["bar"][args]. These values are:
-- nil.
-- -0, which is equivalent to 0 in most situations, but becomes "-0" on conversion to string; it also behaves differently in some operations (e.g. 1/a evaluates to inf if a is 0, but -inf if a is -0).
-- NaN and -NaN, which are the only values for which n == n is false; they only seem to differ on conversion to string ("nan" and "-nan").
local function get_key(input)
-- nil
if input == nil then
if not nil_ then
nil_ = {}
end
return nil_
-- -0
elseif input == 0 and 1 / input < 0 then
if not neg_0 then
neg_0 = {}
end
return neg_0
-- Default
elseif input == input then
return input
-- NaN
elseif format("%f", input) == "nan" then
if not pos_nan then
pos_nan = {}
end
return pos_nan
-- -NaN
elseif not neg_nan then
neg_nan = {}
end
return neg_nan
end
-- Return values are memoized as tables of return values, which are looked up using each input argument as a key, followed by args. e.g. if the input arguments were (1, 2, 3), the memo would be located at t[1][2][3][args]. args is always used as the final lookup key so that (for example) the memo for f(1, 2, 3), f[1][2][3][args], doesn't interfere with the memo for f(1, 2), f[1][2][args].
local function get_memo(memo, n, nargs, key, ...)
key = get_key(key)
local next_memo = memo[key]
if next_memo == nil then
next_memo = {}
memo[key] = next_memo
end
memo = next_memo
return n == nargs and memo or get_memo(memo, n + 1, nargs, ...)
end
-- Catch the function output values, and return the hidden variable arg (which is {...}, and available when a function has ...). We do this instead of catching the output in a table directly, because arg also contains the key "n", which is equal to select("#", ...). i.e. it's the number of arguments in ..., including any nils returned after the last non-nil value (e.g. select("#", nil) == 1, select("#") == 0, select("#", nil, "foo", nil, nil) == 4 etc.). The distinction between nil and nothing affects some native functions (e.g. tostring() throws an error, but tostring(nil) returns "nil"), so it needs to be reconstructable from the memo.
local function catch_output(...)
return arg
end
function export.memoize(func, simple)
if not is_callable(func) then
local _type = type(func)
error(format(
"Only functions and callable tables are memoizable. Received %s.",
_type == "table" and "non-callable table" or _type
))
end
local memo = {}
return simple and function(...)
local key = get_key(...)
local output = memo[key]
if output ~= nil then
if output == nil_ then
return nil
end
return output
end
output = func(...)
if output ~= nil then
memo[key] = output
return output
elseif not nil_ then
nil_ = {}
end
memo[key] = nil_
return nil
end or function(...)
local nargs = select("#", ...)
local memo = nargs == 0 and memo or get_memo(memo, 1, nargs, ...)
if not args then
args = {}
end
local output = memo[args]
if output == nil then
output = catch_output(func(...))
memo[args] = output
end
-- Unpack from 1 to the original number of return values (memoized as output.n); unpack returns nil for any values not in output.
return unpack(output, 1, output.n)
end
end
end
return export