Module:Fun
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Usage
Some meta-functions used in functional programming. See Module:fun on English Wiktionary for documentation.
local p = {}
local ustring = mw.ustring
local libraryUtil = require "libraryUtil"
local checkType = libraryUtil.checkType
local checkTypeMulti = libraryUtil.checkTypeMulti
local iterableTypes = { "table", "string" }
local _checkCache = {}
local function _check(funcName, expectType)
if type(expectType) == "string" then
return function(argIndex, arg, nilOk)
return checkType(funcName, argIndex, arg, expectType, nilOk)
end
else
-- Lua 5.1 doesn't cache functions as Lua 5.3 does.
local checkFunc = _checkCache[funcName]
or 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
_checkCache[funcName] = checkFunc
return checkFunc
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
-- funcName and startArg are for argument type-checking.
-- The varargs (...) can be either an iterator and its optional state and start
-- value, or an iterable type, in which case the function calls the appropriate
-- iterator generator function.
local function getIteratorTriplet(funcName, startArg, ...)
local t = type(...)
if t == "function" then
return ...
end
local first = ...
checkTypeMulti(funcName, startArg, first, iterableTypes)
if t == "string" then
return iterString(first)
elseif first[1] ~= nil then
return ipairs(first)
else
return pairs(first)
end
end
function p.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" }
-- Two argument formats:
-- map(func, iterable)
-- map(func, iterator[, state[, start_value]])
-- func is a function that takes a maximum of two return values of the iterator
-- in reverse order. They are supplied in reverse order because the ipairs
-- iterator returns the index before the value, but the value is most often more
-- important than the index.
-- Any need for map that retains original keys, rather than creating an array?
function p.map(func, keepOriginalKeys, ...)
checkType("map", 1, func, "function")
local iter, state, start_value
if type(keepOriginalKeys) == "boolean" then
iter, state, start_value = getIteratorTriplet("map", 3, ...)
else -- keepOriginalKeys is actually iterator or iterable.
iter, state, start_value = getIteratorTriplet("map", 2, keepOriginalKeys, ...)
keepOriginalKeys = false
end
local result = {}
if keepOriginalKeys then
for val1, val2 in iter, state, start_value do
result[val1] = func(val2, val1, state)
end
else
local i = 0
for val1, val2 in iter, state, start_value do
i = i + 1
result[i] = func(val2, val1, state)
end
end
return result
end
p.mapIter = p.map
local function fold(func, result, ...)
checkType("fold", 1, func, "function")
local iter, state, start_value = getIteratorTriplet("fold", 3, ...)
for val1, val2 in iter, state, start_value do
result = func(result, val2, val1, state)
end
return result
end
p.fold = fold
function p.count(func, ...)
checkType("count", 1, func, "function")
return fold(
function (count, val)
if func(val) then
return count + 1
end
return count
end,
0,
...)
end
function p.forEach(func, ...)
checkType("forEach", 1, func, "function")
local iter, state, start_value = getIteratorTriplet("forEach", 2, ...)
for val1, val2 in iter, state, start_value do
func(val2, val1, state)
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 p.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 p.some(func, ...)
checkType("some", 1, func, "function")
local iter, state, start_value = getIteratorTriplet("some", 2, ...)
for val1, val2 in iter, state, start_value do
if func(val2, val1, state) then
return true
end
end
return false
end
-- all(function(val) return val % 2 == 0 end,
-- { 2, 4, 8, 10, 12 }) --> true
function p.all(func, ...)
checkType("some", 1, func, "function")
local iter, state, start_value = getIteratorTriplet("all", 2, ...)
for val1, val2 in iter, state, start_value do
if not func(val2, val1, state) then
return false
end
end
return true
end
function p.indexOf(func, ...)
local iter, state, start_value = getIteratorTriplet("indexOf", 2, ...)
if type(func) == "function" then
for val1, val2 in iter, state, start_value do
if func(val2, val1, state) then
return val1
end
end
-- func is actually value to search for.
-- Not a great idea to combine these two separate functions.
elseif func ~= nil then -- check for NaN?
for val1, val2 in iter, state, start_value do
if func == val2 then
return val1
end
end
else
error("value to search for is nil")
end
return nil
end
function p.filter(func, ...)
local check = _check
checkType("filter", 1, func, "function")
local new_t = {}
local new_i = 0
local iter, state, start_value = getIteratorTriplet("filter", 2, ...)
for val1, val2 in iter, state, start_value do
if func(val2, val1, state) then
new_i = new_i + 1
new_t[new_i] = val1
end
end
return new_t
end
function p.range(low, high)
low = low - 1
return function ()
if low < high then
low = low + 1
return low
end
end
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 p.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
p.log = p.logReturnValues
-- Convenience function to make all functions in a table log their input and output.
function p.logAll(t)
for k, v in pairs(t) do
if type(v) == "function" then
t[k] = p.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 p.memoize(func)
return setmetatable({ [func_key] = func }, mt)
end
-------------------------------
return p