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Moses: a utility-belt library for functional programming in Lua

Moses is a Lua utility library which provides support for functional programming. It complements built-in Lua functions, making easier common operations on tables, arrays, lists, collections, objects, and a lot more.

Sections

Adding Moses to your project

Drop the file moses.lua into your project and add it to your code with the require function:

local M = require ("moses")

Moses provides a large set of functions that can be classified into four categories:

[⬆]

Table functions

clear (t)

Clears a table. All its values becomes nil. Returns the passed-in table.

M.clear({1,2,'hello',true}) -- => {}

each (t, f)

Aliases: forEach.

Iterates over each value-key pair in the passed-in table.

M.each({4,2,1},print)

-- => 4 1
-- => 2 2
-- => 1 3

The table can be map-like (both array part and hash part).

M.each({one = 1, two = 2, three = 3},print)

-- => 1 one
-- => 2 two
-- => 3 three

Can index and assign in an outer table or in the passed-in table:

t = {'a','b','c'}
M.each(t,function(v,i)
  t[i] = v:rep(2)
  print(t[i])
end)

-- => aa
-- => bb
-- => cc

eachi (t, f)

Aliases: forEachi.

Iterates only on integer keys in an array table. It returns value-key pairs.

M.eachi({4,2,1},print)

-- => 4 1
-- => 2 2
-- => 1 3

The given array can be sparse, or even have a hash-like part.

local t = {a = 1, b = 2, [0] = 1, [-1] = 6, 3, x = 4, 5}
M.eachi(t,print)

-- => 6 -1
-- => 1 0
-- => 3 1	
-- => 5 2

at (t, ...)

Collects values at given keys and returns them in an array.

local t = {4,5,6}
M.at(t,1,3) -- => "{4,6}"

local t = {a = 4, bb = true, ccc = false}
M.at(t,'a', 'ccc') -- => "{4, false}"

adjust (t, key, f)

Adjusts the value at a given key using a function or a value. In case f is a function, it should be prototyped f(v). It does not mutate the given table, but rather returns a new array.

local t = {1,2,3}
M.adjust(t, 2, math.sin) -- => {1, 0.90929, 3}

local v = {x = 1}
 M.adjust(t, 'x', 4) -- => {x = 4}

In case the given key does not exist in t, it throws an error.

count (t [, val])

Counts the number of occurences of a given value in a table.

M.count({1,1,2,3,3,3,2,4,3,2},1) -- => 2
M.count({1,1,2,3,3,3,2,4,3,2},2) -- => 3
M.count({1,1,2,3,3,3,2,4,3,2},3) -- => 4
M.count({false, false, true},false) -- => 2
M.count({false, false, true},true) -- => 1

Returns the size of the list in case no value was provided.

M.count({1,1,2,3,3}) -- => 5

countf (t, f)

Counts the number of values passing an iterator test.

M.countf({1,2,3,4,5,6}, function(v)
  return v%2==0
end) -- => 3

M.countf({print, pairs, os, assert, ipairs}, function(v)
  return type(v)=='function'
end) -- => 4

allEqual (t [, comp])

Aliases: alleq.

Checks if all values in a collection are equal. Uses M.isEqual by default to compare values.

M.allEqual({1,1,1,1,1}, comp) -- => true
M.allEqual({1,1,2,1,1}, comp) -- => false

local t1 = {1, 2, {3}}
local t2 = {1, 2, {3}}
M.allEqual({t1, t2}) -- => true

Can take an optional comp function which will be used to compare values.

local t1 = {x = 1, y = 0}
local t2 = {x = 1, y = 0}
local t3 = {x = 1, y = 2}
local t4 = {x = 1, y = 2}
local function compx(a, b) return a.x == b.x end
local function compy(a, b) return a.y == b.y end

M.allEqual({t1, t2}, compx) -- => true
M.allEqual({t1, t2}, compy) -- => true
M.allEqual({t3, t4}, compx) -- => true
M.allEqual({t3, t4}, compy) -- => true
M.allEqual({t1, t2, t3, t4}, compx) -- => true
M.allEqual({t1, t2, t3, t4}, compy) -- => false

cycle (t [, n = 1])

Aliases: loop.

Returns a function which iterates on each value-key pair in a given table (similarly to M.each), except that it restarts iterating again n times. If n is not provided, it defaults to 1.

local t = {'a','b','c'}
for v in M.cycle(t, 2) do
  print(v)
end

-- => 'a'
-- => 'b'
-- => 'c'
-- => 'a'
-- => 'b'
-- => 'c'

Supports array-like tables and map-like tables.

local t = {x = 1, y = 2, z = 3}
for v in M.cycle(t) do
  print(v)
end

-- => 2
-- => 1
-- => 3

map (t, f)

Aliases: collect.

Executes a function on each value in a given array.

M.map({1,2,3},function(v) 
  return v+10 
end) -- => "{11,12,13}"
M.map({a = 1, b = 2},function(v, k) 
  return k..v 
end) -- => "{a = 'a1', b = 'b2'}"

It also maps both keys and values.

M.map({a = 1, b = 2},function(v, k) 
  return k..k, v*2 
end) -- => "{aa = 2, bb = 4}"

reduce (t, f [, state = next(t)])

Aliases: inject, foldl.

Can sum all values in a table. In case state is not provided, it defaults to the first value in the given table t.

local function add(a,b) return a+b end
M.reduce({1,2,3,4},add) -- => 10

Or concatenates all values.

local function concat(a,b) return a..b end	
M.reduce({'a','b','c','d'},concat) -- => abcd	 

best (t, f)

Returns the best value passing a selector function. Acts as a special case of reduce, using the first value in t as an initial state. It thens folds the given table, testing each of its values v and selecting the value passing the call f(state,v) every time.

local words = {'Lua', 'Programming', 'Language'}
M.best(words, function(a,b) return #a > #b end) -- => 'Programming'
M.best(words, function(a,b) return #a < #b end) -- => 'Lua'

reduceBy (t, f, pred [, state = next(t)])

Reduces a table considering only values matching a predicate. For example,let us define a set of values.

local val = {-1, 8, 0, -6, 3, -1, 7, 1, -9}

And a reduction function which will add up values.

local function add(a,b) return a+b end

We can also define some predicate functions.

-- predicate for negative values
local function neg(v) return v<=0 end

-- predicate for positive values
local function pos(v) return v>=0 end

Then we can perform reduction considering only negative or positive values :

M.reduceBy(val, add, neg) -- => -17
M.reduceBy(val, add, pos) -- => 19

An initial state can be passed in.

M.reduceBy(val, add, neg, 17) -- => 0
M.reduceBy(val, add, pos, -19) -- => 0

reduceRight (t, f [, state = next(t)])

Aliases: injectr, foldr.

Similar to M.reduce, but performs from right to left.

local initial_state = 256
local function div(a,b) return a/b end
M.reduceRight({1,2,4,16},div,initial_state) -- => 2

mapReduce (t, f [, state = next(t)])

Aliases: mapr.

Reduces while saving intermediate states.

local function concat(a,b) return a..b end
M.mapReduce({'a','b','c'},concat) -- => "{'a', 'ab', 'abc'}"

mapReduceRight (t, f [, state = next(t)])

Aliases: maprr.

Reduces from right to left, while saving intermediate states.

local function concat(a,b) return a..b end
M.mapReduceRight({'a','b','c'},concat) -- => "{'c', 'cb', 'cba'}"

include (t, value)

Aliases: any, some, contains.

Looks for a value in a table.

M.include({6,8,10,16,29},16) -- => true
M.include({6,8,10,16,29},1) -- => false

local complex_table = {18,{2,{3}}}
local collection = {6,{18,{2,6}},10,{18,{2,{3}}},29}
M.include(collection, complex_table) -- => true

Handles iterator functions.

local function isUpper(v) return v:upper()== v end
M.include({'a','B','c'},isUpper) -- => true

detect (t, value)

Returns the index of a value in a table.

M.detect({6,8,10,16},8) -- => 2
M.detect({nil,true,0,true,true},false) -- => nil

local complex_table = {18,{2,6}}
local collection = {6,{18,{2,6}},10,{18,{2,{3}}},29}
M.detect(collection, complex_table) -- => 2

Handles iterator functions.

local function isUpper(v)
  return v:upper()==v
end
M.detect({'a','B','c'},isUpper) -- => 2

where (t, props)

Looks through a table and returns all the values that matches all of the key-value pairs listed in props.

local items = {
  {height = 10, weight = 8, price = 500},
  {height = 10, weight = 15, price = 700},
  {height = 15, weight = 15, price = 3000},
  {height = 10, weight = 8, price = 3000},
}
M.where(items, {height = 10}) -- => {items[1], items[2], items[4]}
M.where(items, {weight = 15}) -- => {items[2], items[3]}
M.where(items, {prince = 3000}) -- => {items[3], items[4]}
M.where(items, {height = 10, weight = 15, prince = 700}) -- => {items[2]}

findWhere (t, props)

Looks through a table and returns the first value found that matches all of the key-value pairs listed in props.

local a = {a = 1, b = 2, c = 3}
local b = {a = 2, b = 3, d = 4}
local c = {a = 3, b = 4, e = 5}
M.findWhere({a, b, c}, {a = 3, b = 4}) == c -- => true

select (t, f)

Aliases: filter.

Collects values passing a validation test.

local function isEven(v) return v%2==0 end
local function isOdd(v) return v%2~=0 end

M.select({1,2,3,4,5,6,7}, isEven) -- => "{2,4,6}"
M.select({1,2,3,4,5,6,7}, isOdd) -- => "{1,3,5,7}"

reject (t, f)

Aliases: reject.

Removes all values failing (returning false or nil) a validation test:

local function isEven(v) return v%2==0 end
local function isOdd(v) return v%2~=0 end

M.reject({1,2,3,4,5,6,7}, isEven) -- => "{1,3,5,7}"
M.reject({1,2,3,4,5,6,7}, isOdd) -- => "{2,4,6}"

all (t, f)

Aliases: every.

Checks whether or not all elements pass a validation test.

local function isEven(v) return v%2==0 end
M.all({2,4,6}, isEven) -- => true

invoke (t, method)

Invokes a given function on each value in a table.

M.invoke({'a','bea','cdhza'},string.len) -- => "{1,3,5}"

Can reference the method of the same name in each value.

local a, b, c, d = {id = 'a'}, {id = 'b'}, {id = 'c'}, {id = 'd'}
local function call(self) return self.id end
M.invoke({a,b,c,d},call) -- => "{'a','b','c','d'}"

pluck (t, property)

Fetches all values indexed with specific key in a table of objects.

local peoples = {
  {name = 'John', age = 23},{name = 'Peter', age = 17},
  {name = 'Steve', age = 15},{age = 33}}

M.pluck(peoples,'age') -- => "{23,17,15,33}"
M.pluck(peoples,'name') -- => "{'John', 'Peter', 'Steve'}"

max (t [, transform])

Returns the maximum value in a collection.

M.max {1,2,3} -- => 3
M.max {'a','b','c'} -- => 'c'

Can take an iterator function to extract a specific property.

local peoples = {
  {name = 'John', age = 23},{name = 'Peter', age = 17},
  {name = 'Steve', age = 15},{age = 33}}
M.max(peoples,function(people) return people.age end) -- => 33

min (t [, transform])

Returns the minimum value in a collection.

M.min {1,2,3} -- => 1
M.min {'a','b','c'} -- => 'a'

Can take an iterator function to extract a specific property.

local peoples = {
  {name = 'John', age = 23},{name = 'Peter', age = 17},
  {name = 'Steve', age = 15},{age = 33}}
M.min(peoples,function(people) return people.age end) -- => 15

same (a, b)

Tests whether or not all values in each of the passed-in tables exists in both tables.

local a = {'a','b','c','d'}      
local b = {'b','a','d','c'}
M.same(a,b) -- => true

b[#b+1] = 'e'
M.same(a,b) -- => false

sort (t [, comp = math.min])

Sorts a collection.

M.sort({'b','a','d','c'}) -- => "{'a','b','c','d'}"

Handles custom comparison functions.

M.sort({'b','a','d','c'}, function(a,b) 
  return a:byte() > b:byte() 
end) -- => "{'d','c','b','a'}"

sortedk (t [, comp])

Iterates on values with respect to key order. Keys are sorted using comp function which defaults to math.min. It returns upon each call a key, value pair.

local tbl = {}; tbl[3] = 5 ; tbl[2] = 6; tbl[5] = 8; tbl[4] = 10; tbl[1] = 12
for k, v in M.sortedk(tbl) do print(k, v) end

-- => 1	12
-- => 2	6
-- => 3	5
-- => 4	10
-- => 5	8

local function comp(a,b) return a > b end
for k, v in M.sortedk(tbl, comp) do print(k, v) end

-- => 5	8
-- => 4	10
-- => 3	5
-- => 2	6
-- => 1	12

sortedv (t [, comp])

Iterates on values with respect to key order. Keys are sorted using comp function which defaults to math.min. It returns upon each call a key, value pair.

local tbl = {}; tbl[3] = 5 ; tbl[2] = 6; tbl[5] = 8; tbl[4] = 10; tbl[1] = 12
for k, v in M.sortedv(tbl) do print(k, v) end

-- => 3	5
-- => 2	6
-- => 5	8
-- => 4	10
-- => 1	12

local function comp(a,b) return a > b end
for k, v in M.sortedv(tbl, comp) do print(k, v) end

-- => 1	12
-- => 4	10
-- => 5	8
-- => 2	6
-- => 3	5

sortBy (t [, transform [, comp = math.min]])

Sorts items in a collection based on the result of running a transform function through every item in the collection.

local r = M.sortBy({1,2,3,4,5}, math.sin)
print(table.concat(r,','))

-- => {5,4,3,1,2}

The transform function can also be a string name property.

local people = {
	{name = 'albert', age = 40},
	{name = 'louis', age = 55},
	{name = 'steve', age = 35},
	{name = 'henry', age = 19},
}
local r = M.sortBy(people, 'age')
M.each(r, function(v) print(v.age, v.name)	end)

-- => 19	henry
-- => 35	steve
-- => 40	albert
-- => 55	louis

As seen above, the defaut comparison function is the '<' operator. For example, let us supply a different one to sort the list of people by decreasing age order :

local people = {
	{name = 'albert', age = 40},
	{name = 'louis', age = 55},
	{name = 'steve', age = 35},
	{name = 'henry', age = 19},
}
local r = M.sortBy(people, 'age', function(a,b) return a > b end)
M.each(r, function(v) print(v.age, v.name)	end)

-- => 55	louis
-- => 40	albert
-- => 35	steve
-- => 19	henry

The transform function defaults to M.indentity and in that case, M.sortBy behaves like M.sort.

local r = M.sortBy({1,2,3,4,5})
print(table.concat(r,','))

-- => {1,2,3,4,5}

groupBy (t, iter)

Groups values in a collection depending on their return value when passed to a predicate test.

M.groupBy({0,1,2,3,4,5,6},function(v) 
  return v%2==0 and 'even' or 'odd'
end)
-- => "{odd = {1,3,5}, even = {0,2,4,6}}"

M.groupBy({0,'a',true, false,nil,b,0.5},type) 
-- => "{number = {0,0.5}, string = {'a'}, boolean = {true, false}}"		

countBy (t, iter)

Splits a table in subsets and provide the count for each subset.

M.countBy({0,1,2,3,4,5,6},function(v) 
  return v%2==0 and 'even' or 'odd'
end) -- => "{odd = 3, even = 4}"

size (...)

When given a table, provides the count for the very number of values in that table.

M.size {1,2,3} -- => 3
M.size {one = 1, two = 2} -- => 2

When given a vararg list of arguments, returns the count of these arguments.

M.size(1,2,3) -- => 3
M.size('a','b',{}, function() end) -- => 4

containsKeys (t, other)

Checks whether a table has all the keys existing in another table.

M.contains({1,2,3,4},{1,2,3}) -- => true
M.contains({1,2,'d','b'},{1,2,3,5}) -- => true
M.contains({x = 1, y = 2, z = 3},{x = 1, y = 2}) -- => true

sameKeys (tA, tB)

Checks whether both tables features the same keys:

M.sameKeys({1,2,3,4},{1,2,3}) -- => false
M.sameKeys({1,2,'d','b'},{1,2,3,5}) -- => true
M.sameKeys({x = 1, y = 2, z = 3},{x = 1, y = 2}) -- => false

[⬆]

Array functions

sample (array [, n = 1 [, seed]])

Samples n values from array.

local array = M.range(1,20)
local sample = M.sample(array, 3)
print(table.concat(sample,','))

-- => {12,11,15}

n defaults to 1. In that case, a single value will be returned.

local array = M.range(1,20)
local sample = M.sample(array)
print(sample)

-- => 12

An optional 3rd argument seed can be passed for deterministic random sampling.

sampleProb (array, prob [, seed])

Returns an array of values randomly selected from a given array. In case seed is provided, it is used for deterministic sampling.

local array = M.range(1,20)
local sample = M.sampleProb(array, 0.2)
print(table.concat(sample,','))

-- => 5,11,12,15

sample = M.sampleProb(array, 0.2, os.time())
print(table.concat(sample,','))

-- => 1,6,10,12,15,20 (or similar)

nsorted (array [, n = 1[, comp]])

Returns the n-top values satisfying a predicate. It takes a comparison function comp used to sort array values, and then picks the top n-values. It leaves the original array untouched.

local function comp(a,b) return a > b end
M.nsorted(array,5, comp) -- => {5,4,3,2,1}

n defaults to 1 and comp defaults to the < operator.

local array = M.range(1,20)
M.nsorted(array) -- => {1}

shuffle (array [, seed])

Shuffles a given array.

local list = M.shuffle {1,2,3,4,5,6} -- => "{3,2,6,4,1,5}"
M.each(list,print)

pack (...)

Converts a vararg list of arguments to an array.

M.pack(1,2,8,'d','a',0) -- => "{1,2,8,'d','a',0}"

find (array, value [, from = 1])

Looks for a value in a given array and returns the position of the first occurence.

local value = {3}
M.find({{4},{3},{2},{1}},value) -- => 2

It can also start the search at a specific position in the array:

-- search value 4 starting from index 3
M.find({1,4,2,3,4,5},4,3) -- => 5

reverse (array)

Reverses an array.

M.reverse({1,2,3,'d'}) -- => "{'d',3,2,1}"

fill (array, value [, i = 1 [, j = #array]])

Replaces all elements in a given array with a given value.

local array = M.range(1,5)
M.fill(array, 0) -- => {0,0,0,0,0}

It can start replacing value at a specific index.

local array = M.range(1,5)
M.fill(array,0,3) -- => {1,2,0,0,0}

It can replace only values within a specific range.

local array = M.range(1,5)
M.fill(array,0,2,4) -- => {1,0,0,0,5}

In case the upper bound index i greather than the array size, it will enlarge the array.

local array = M.range(1,5)
M.fill(array,0,5,10) -- => {1,2,3,4,0,0,0,0,0,0}

zeros (n)

Returns an array of n zeros.

M.zeros(4) -- => {0,0,0,0}

ones (n)

Returns an array of n 1's.

M.ones(3) -- => {1,1,1}

vector (value, n)

Returns an array of n times a given value.

M.vector(10, 4) -- => {10,10,10,10}

selectWhile (array, f [, ...])

Aliases: takeWhile.

Collects values as long as they pass a given test. Stops on the first non-passing test.

M.selectWhile({2,4,5,8}, function(v)
  return v%2==0
end) -- => "{2,4}"

dropWhile (array, f [, ...])

Aliases: rejectWhile.

Removes values as long as they pass a given test. Stops on the first non-passing test.

M.dropWhile({2,4,5,8}, function(v)
  return v%2==0
end) -- => "{5,8}"

sortedIndex (array, value [, comp = math.min [, sort = nil]])

Returns the index at which a value should be inserted to preserve order.

M.sortedIndex({1,2,3},4) -- => 4

Can take a custom comparison functions.

local comp = function(a,b) return a<b end
M.sortedIndex({-5,0,4,4},3,comp) -- => 3

indexOf (array, value)

Returns the index of a value in an array.

M.indexOf({1,2,3},2) -- => 2

lastIndexOf (array, value)

Returns the index of the last occurence of a given value in an array.

M.lastIndexOf({1,2,2,3},2) -- => 3

findIndex (array, pred)

Returns the first index at which a predicate passes a truth test.

local array = {1,2,3,4,5,6}
local function multipleOf3(v) return v%3==0 end
M.findIndex(array, multipleOf3) -- => 3

findLastIndex (array, pred)

Returns the last index at which a predicate passes a truthy test.

local array = {1,2,3,4,5,6}
local function multipleOf3(v) return v%3==0 end
M.findLastIndex(array, multipleOf3) -- => 6

addTop (array, ...)

Adds given values at the top of an array. The latter values bubbles at the top.

local array = {1}
M.addTop(array,1,2,3,4) -- => "{4,3,2,1,1}"

prepend (array, ...)

Adds given values at the top of an array, preserving the order at which elements are passed-in.

local array = {'old_val'}
M.prepend(array,1,2,3,4) -- => "{1,2,3,4,'old_val'}"

push (array, ...)

Adds given values at the end of an array.

local array = {1}
M.push(array,1,2,3,4) -- => "{1,1,2,3,4}"

shift (array [, n = 1])

Aliases: pop.

Removes and returns the first value in an array.

local array = {1,2,3}
local shift = M.shift(array) -- => "shift = 1", "array = {2,3}"

If n is supplied, returns n values.

local array = {1,2,3,4,5}
local a, b = M.shift(array, 2) -- => "a = 1, b = 2", "array = {3,4,5}"

unshift (array [, n = 1])

Removes and returns the last value in an array.

local array = {1,2,3}
local value = M.unshift(array) -- => "value = 3", "array = {1,2}"

pull (array, ...)

Aliases: remove.

Removes all provided values from a given array.

M.pull({1,2,1,2,3,4,3},1,2,3) -- => "{4}"

removeRange (array [, start = 1 [, finish = #array]])

Aliases: rmRange, M.chop.

Trims out all values index within a range.

local array = {1,2,3,4,5,6,7,8,9}
M.removeRange(array, 3,8) -- => "{1,2,9}"

chunk (array, f)

Iterates over an array aggregating consecutive values in subsets tables, on the basis of the return value of f(v, k, ...). Consecutive elements which return the same value are chunked together.

local t = {1,1,2,3,3,4}
M.chunk(t, function(v) return v%2==0 end) -- => "{{1,1},{2},{3,3},{4}}"

slice (array [, start = 1 [, finish = #array]])

Aliases: sub.

Slices and returns a part of an array.

local array = {1,2,3,4,5,6,7,8,9}
M.slice(array, 3,6) -- => "{3,4,5,6}"

first (array [, n = 1])

Aliases: head, M.take.

Returns the first N elements in an array.

local array = {1,2,3,4,5,6,7,8,9}
M.first(array,3) -- => "{1,2,3}"

initial (array [, n = #array])

Excludes the last N elements in an array.

local array = {1,2,3,4,5,6,7,8,9}
M.initial(array,5) -- => "{1,2,3,4}"

last (array [, n = #array])

Returns the last N elements in an array.

local array = {1,2,3,4,5,6,7,8,9}
M.last(array,3) -- => "{7,8,9}"

rest (array [, index = 1])

Aliases: tail.

Returns all values after index, including the given index itself.

local array = {1,2,3,4,5,6,7,8,9}
M.rest(array,6) -- => "{6,7,8,9}"

nth (array, index)

Returns the value at index.

local array = {1,2,3,4,5,6}
M.nth(array,3) -- => "3"

compact (array)

Trims out all falsy values.

M.compact {a,'aa',false,'bb',true} -- => "{'aa','bb',true}"

flatten (array [, shallow = false])

Flattens a nested array.

M.flatten({1,{2,3},{4,5,{6,7}}}) -- => "{1,2,3,4,5,6,7}"

When given arg shallow, flatten only at the first level.

M.flatten({1,{2},{{3}}},true) -- => "{1,{2},{{3}}}"

difference (array, array2)

Aliases: without, diff.

Returns values in the given array not present in a second array.

local array = {1,2,'a',4,5}
M.difference(array,{1,'a'}) -- => "{2,4,5}"

union (...)

Produces a duplicate-free union of all passed-in arrays.

local A = {'a'}
local B = {'a',1,2,3}
local C = {2,10}
M.union(A,B,C) -- => "{'a',1,2,3,10}"

intersection (...)

Returns the intersection (common-part) of all passed-in arrays:

local A = {'a'}
local B = {'a',1,2,3}
local C = {2,10,1,'a'}
M.intersection(A,B,C) -- => "{'a'}"

disjoint (...)

Checks if all passed in arrays are disjoint.

local A = {'a'}
local B = {'a',1,3}
local C = {3,10,2}

M.disjoint(A,B) -- => false
M.disjoint(A,C) -- => true
M.disjoint(B,C) -- => false

symmetricDifference (array, array2)

Aliases: symdiff,xor.

Returns values in the first array not present in the second and also values in the second array not present in the first one.

local array = {1,2,3}
local array2 = {1,4,5}
M.symmetricDifference(array, array2) -- => "{2,3,4,5}"

unique (array)

Aliases: uniq.

Makes an array duplicate-free.

M.unique {1,1,2,2,3,3,4,4,4,5} -- => "{1,2,3,4,5}"

isunique (array)

Aliases: isuniq.

Checks if a given array contains no duplicate value.

M.isunique({1,2,3,4,5}) -- => true
M.isunique({1,2,3,4,4}) -- => false

duplicates (array)

Returns an array list of all duplicates in array.

M.duplicates({1,2,3,3,8,8,3,2,4}) -- => {2,3,8}

zip (...)

Aliases: transpose.

Zips values from different arrays, on the basis on their common keys.

local names = {'Bob','Alice','James'}
local ages = {22, 23}
M.zip(names,ages) -- => "{{'Bob',22},{'Alice',23},{'James'}}"

zipWith (f, ...)

Aliases: transposeWith.

Merges values using a given function. Only values indexed with the same key in the given arrays are merged in the same subset. Function f is used to combine values.

local names = {'Bob','Alice','James'}; local ages = {22, 23, 25}
local function introduce(name, age) return 'I am '..name..' and I am '..age..' years old.' end
local t = M.zipWith(introduce,names,ages)
-- => {
-- =>  'I am Bob and I am 22 years old.'
-- =>  'I am Alice and I am 23 years old.'
-- =>  'I am James and I am 25 years old.'
-- => }

append (array, other)

Appends two arrays.

M.append({1,2,3},{'a','b'}) -- => "{1,2,3,'a','b'}"

interleave (...)

Interleaves values from passed-in arrays.

t1 = {1, 2, 3}
t2 = {'a', 'b', 'c'}
M.interleave(t1, t2) -- => "{1,'a',2,'b',3,'c'}"

interpose (array, value)

Aliases: intersperce.

Interposes a value between consecutive values in an arrays.

M.interleave('a', {1,2,3}) -- => "{1,'a',2,'a',3}"

range ([from [, to [, step]]])

Generates an arithmetic sequence.

M.range(1,4) -- => "{1,2,3,4}"

In case a single value is provided, it generates a sequence from 1 to that value.

M.range(3) -- => "{1,2,3}"

The incremental step can also be provided as third argument.

M.range(0,2,0.7) -- => "{0,0.7,1.4}"

It also handles negative progressions.

M.range(-5) -- => "{-1,-2,-3,-4,-5}"
M.range(5,1) -- => "{5,4,3,2,1}"

rep (value, n)

Generates a list of n repetitions of a value.

M.rep(4,3) -- => "{4,4,4}"

powerset (array)

Returns the powerset of an array.

M.powerset {1,2,3} -- => "{{1},{2},{3},{1,2},{2,3},{1,2,3}}"

partition (array [, n = 1 [, pad]])

Aliases: part.

Returns an iterator function for partitions of a given array.

local t = {1,2,3,4,5,6}
for p in M.partition(t,2) do
  print(table.concat(p, ','))
end

-- => 1,2
-- => 3,4
-- => 5,6

local t = {1,2,3,4,5,6}
for p in M.partition(t,4) do
  print(table.concat(p, ','))
end

-- => 1,2,3,4
-- => 5,6

In case the last partition has less elements than desired, a 3rd argument can be supplied to adjust the partition size.

local t = {1,2,3,4,5,6}
for p in M.partition(t,4,0) do
  print(table.concat(p, ','))
end

-- => 1,2,3,4
-- => 5,6,0,0

overlapping (array [, n = 2 [, pad]])

Returns an iterator function which provides overlapping subsequences of a given array.

local t = {1,2,3,4,5,6,7}
for p in M.overlapping(t,3) do
	print(table.concat(p,','))
end

-- => 1,2,3
-- => 3,4,5
-- => 5,6,7

for p in M.overlapping(t,4) do
	print(table.concat(p,','))
end

-- => 1,2,3,4
-- => 4,5,6,7

for p in M.overlapping(t,5) do
	print(table.concat(p,','))
end

-- => 1,2,3,4,5
-- => 5,6,7

In case the last subsequence wil not match the exact desired length, it can be adjusted with a 3rd argument pad.

local t = {1,2,3,4,5,6,7}
for p in M.overlapping(t,5,0) do
	print(table.concat(p,','))
end

-- => 1,2,3,4,5
-- => 5,6,7,0,0

aperture (array [, n = 2])

Aliases: sliding.

Returns an iterator function which provides sliding partitions of a given array.

local t = {1,2,3,4,5}
for p in M.aperture(t,4) do
  print(table.concat(p,','))
end

-- => 1,2,3,4
-- => 2,3,4,5

for p in M.aperture(t,3) do
  print(table.concat(p,','))
end

-- => 1,2,3
-- => 2,3,4
-- => 3,4,5

pairwise (array)

Iterator returning sliding pairs of an array.

local t = M.range(5)
for p in pairwise(t) do
  print(table.concat(p,','))
end

-- => 1,2
-- => 2,3
-- => 3,4
-- => 4,5

permutation (array)

Aliases: perm.

Returns an iterator function for permutations of a given array.

t = {'a','b','c'}
for p in M.permutation(t) do
  print(table.concat(p))
end

-- => 'bca'
-- => 'cba'
-- => 'cab'
-- => 'acb'
-- => 'bac'
-- => 'abc'

concat (array [, sep = '' [, i = 1 [, j = #array]]])

Aliases: join.

Concatenates a given array values:

M.concat({'a',1,0,1,'b'}) -- => 'a101b'

xprod (array, array2)

Returns all possible pairs built from given arrays.

local t = M.xprod({1,2},{'a','b'})
-- => {{1,'a'},{1,'b'},{2,'a'},{2,'b'}}

xpairs (value, array)

Creates pairs from value and array. Value is always prepended to the pair.

local t = M.xpairs(1, {1, 2, 3})
-- => {{1,1},{1,2},{1,3}}

xpairsRight (value, array)

Creates pairs from value and array. Value is always appended as the last item to the pair.

local t = M.xpairsRight(1, {1, 2, 3})
-- => {{1,1},{2,1},{3,1}}

sum (array)

Returns the sum of array values.

M.sum({1,2,3,4,5}) -- => 15

product (array)

Returns the product of array values.

M.product({1,2,3,4,5}) -- => 120

mean (array)

Returns the mean of array values.

M.mean({1,2,3,4,5}) -- => 3

median (array)

Returns the median of array values.

M.median({1,2,3,4,5}) -- => 3
M.median({1,2,3,4}) -- => 2.5

[⬆]

Utility functions

noop ()

The no-operation function. Takes nothing, returns nothing. It is being used internally.

M.noop() -- => nil

identity (value)

Returns the passed-in value.
This function is internally used as a default transformation function.

M.identity(1)-- => 1
M.identity(false) -- => false
M.identity('hello!') -- => 'hello!'

call (f [, ...])

Calls f with the supplied arguments. Returns the results of f(...).

M.call(math.pow, 2, 3) -- => 8
M.call(string.len, 'hello' ) -- => 5
M.call(table.concat, {1,2,3,4,5}, ',', 2, 4) -- => {2,3,4}

constant (value)

Creates a constant function. This function will continuously yield the same output.

local pi = M.constant(math.pi)
pi(1) -- => 3.1415926535898
pi(2) -- => 3.1415926535898
pi(math.pi) -- => 3.1415926535898

applySpec (specs)

Returns a function which applies specs on args. This function will produce an object having the same structure than specs by mapping each property to the result of calling its associated function with the supplied arguments.

local stats = M.applySpec({
  min = function(...) return math.min(...) end,
  max = function(...) return math.max(...) end,
})

stats(5,4,10,1,8) -- => {min = 1, max = 10}

thread (value [, ...])

Threads value through a series of functions.

local function inc(x) return x + 1 end
local function double(x) return 2 * x end
local function square(x) return x * x end
M.thread(2, inc, double, square) -- => 36
M.thread(3, double, inc, square) -- => 49
M.thread(4, square, double, inc) -- => 33
M.thread(5, square, inc, double) -- => 52

If a function expects more than one args, it can be specified using an array list, where the first item is the function and the following are the remaining args neeeded.

local function inc(x) return x + 1 end
local function add(x, y) return x * y end
local function pow(x, y) return x ^ y end
M.thread(2, inc, {add, 3}, {pow, 2}) -- => 36
M.thread(2, {add, 4}, inc, {pow, 2}) -- => 49

threadRight (value [, ...])

Threads value through a series of functions. If a function expects more than one args, it can be specified using an array list, where the first item is the function and the following are the remaining args neeeded. The value is used as the last input.

local function inc(x) return x + 1 end
local function add(x, y) return x * y end
local function pow(x, y) return x ^ y end
M.threadRight(2, inc, {add, 3}, {pow, 2}) -- => 64
M.threadRight(2, {add, 4}, inc, {pow, 2}) -- => 128

dispatch (...)

Returns a dispatching function. When called with arguments, this function invokes each of its functions in the passed-in order and returns the results of the first non-nil evaluation.

local f = M.dispatch(
  function() return nil end,
  function (v) return v+1 end, 
  function (v) return 2*v end
)
f(5) -- => 6
f(7) -- => 8

memoize (f)

Aliases: cache.

Memoizes a slow-running function. It caches the result for a specific input, so that the next time the function is called with the same input, it will lookup the result in its cache, instead of running again the function body.

local function fibonacci(n)
  return n < 2 and n or fibonacci(n-1)+fibonacci(n-2)
end  
local mem_fibonacci = M.memoize(fibonacci)
fibonacci(20) -- => 6765 (but takes some time)
mem_fibonacci(20) -- => 6765 (takes less time)

unfold (f, seed)

Builds a list from a seed value. Accepts an iterator function, which returns either nil to stop iteration or two values : the value to add to the list of results and the seed to be used in the next call to the iterator function.

local function f(v)
  if v < 100 then return v, v * 2 end
end
local t = M.unfold(f, 10) -- => {10,20,40,80}

once (f)

Produces a function that runs only once. Successive calls to this function will still yield the same input.

local sq = M.once(function(a) return a*a end)
sq(1) -- => 1
sq(2) -- => 1
sq(3) -- => 1
sq(4) -- => 1
sq(5) -- => 1

before (f, count)

Returns a version of f that will run no more than count times. Next calls will keep yielding the results of the (n-th)-1 call.

local function greet(someone) return 'hello '..someone end
local greetOnly3people = M.before(greet, 3)
greetOnly3people('John') -- => 'hello John'
greetOnly3people('Moe') -- => 'hello Moe'
greetOnly3people('James') -- => 'hello James'
greetOnly3people('Joseph') -- => 'hello James'
greetOnly3people('Allan') -- => 'hello James'

after (f, count)

Produces a function that will respond only after a given number of calls.

local f = M.after(M.identity,3)
f(1) -- => nil
f(2) -- => nil
f(3) -- => 3
f(4) -- => 4

compose (...)

Composes functions. Each function consumes the return value of the one that follows.

local function f(x) return x^2 end
local function g(x) return x+1 end
local function h(x) return x/2 end
local compositae = M.compose(f,g,h)
compositae(10) -- => 36
compositae(20) -- => 121

pipe (value, ...)

Pipes a value through a series of functions.

local function f(x) return x^2 end
local function g(x) return x+1 end
local function h(x) return x/2 end
M.pipe(10,f,g,h) -- => 36
M.pipe(20,f,g,h) -- => 121

complement (f)

Returns a function which returns the logical complement of a given function.

M.complement(function() return true end)() -- => false

juxtapose (value, ...)

Aliases: juxt.

Calls a sequence of functions with the same input.

local function f(x) return x^2 end
local function g(x) return x+1 end
local function h(x) return x/2 end
M.juxtapose(10, f, g, h) -- => 100, 11, 5

wrap (f, wrapper)

Wraps a function inside a wrapper. Allows the wrapper to execute code before and after function run.

local greet = function(name) return "hi: " .. name end
local greet_backwards = M.wrap(greet, function(f,arg)
  return f(arg) ..'\nhi: ' .. arg:reverse()
end) 
greet_backwards('John')

-- => hi: John
-- => hi: nhoJ

times (iter [, n])

Calls a given function n times.

local f = ('Lua programming'):gmatch('.')
M.times(f, 3) -- => {'L','u','a'}

bind (f, v)

Binds a value to be the first argument to a function.

local sqrt2 = M.bind(math.sqrt,2)
sqrt2() -- => 1.4142135623731

bind2 (f, v)

Binds a value to be the second argument to a function.

local last2 = M.bind(M.last,2)
last2({1,2,3,4,5,6}) -- => {5,6}

bindn (f, ...)

Binds a variable number of values to be the first arguments to a function.

local function out(...) return table.concat {...} end
local out = M.bindn(out,'OutPut',':',' ')
out(1,2,3) -- => OutPut: 123
out('a','b','c','d') -- => OutPut: abcd

bindall (obj, ...)

Binds methods to object. As such, when calling any of these methods, they will receive object as a first argument.

local window = {
	setPos = function(w,x,y) w.x, w.y = x, y end, 
	setName = function(w,name) w.name = name end,
	getName = function(w) return w.name end,
}
window = M.bindall(window, 'setPos', 'setName', 'getName')
window.setPos(10,15)
print(window.x, window.y) -- => 10,15

window.setName('fooApp')
print(window.name) -- => 'fooApp'

print(window.getName()) -- => 'fooApp'

cond (conds)

Returns a function which iterate over an array list of conditions. It invokes each predicate, passing it given values. It returns the value of the corresponding function of the first predicate to return a non-nil value

local multipleOf = M.cond({
  {function(v) return v%2==0 end, function(v) return v..' is multiple of 2' end},
  {function(v) return v%3==0 end, function(v) return v..' is multiple of 3' end},
  {function(v) return v%5==0 end, function(v) return v..' is multiple of 5' end},
  {function() return true end, function(v) return 'could not find an answer for '..v end}
})
for i = 15, 20 do
  print(multipleOf(i))
end

-- => 15 is multiple of 3
-- => 16 is multiple of 2
-- => could not find an answer for 17
-- => 18 is multiple of 2
-- => could not find an answer for 19
-- => 20 is multiple of 2

both (...)

Returns a validation function. Given a set of functions, the validation function evaluates to true only when all its funcs returns true.

local f = M.both(
	function(x) return x > 0 end,
	function(x) return x < 10 end,
	function(x) return x % 2 == 0 end
)
f(2) -- => true
f(8) -- => true
f(9) -- => false

either (...)

Returns a validation function. Given a set of functions, the validation function evaluates to true when one of its funcs returns true.

local f = M.either(
	function(x) return x > 0 end,
	function(x) return x % 2 == 0 end
)
f(0) -- => true
f(-3) -- => false

neither (...)

Returns a validation function. Given a set of functions, the validation function evaluates to true when neither of its funcs returns true.

local f = M.neither(
	function(x) return x > 10 end,
	function(x) return x % 2 == 0 end
)
f(12) -- => false
f(8) -- => false
f(7) -- => true

uniqueId ([template])

Aliases: uid.

Returns an unique integer ID.

M.uniqueId() -- => 1

Can handle string templates for formatted output.

M.uniqueId('ID%s') -- => 'ID2'

Or a function, for the same purpose.

local formatter = function(ID) return '$'..ID..'$' end
M.uniqueId(formatter) -- => '$ID1$'

iterator (f, value [, n])

Aliases: iter.

Returns an iterator function which constinuously applies a function f onto an input value. For example, let us go through the powers of two using iterator.

local function po2(x) return x*2 end
local function iter_po2 = M.iterator(po2, 1)
iter_po2() -- => 2
iter_po2() -- => 4
iter_po2() -- => 8

if n is supplied, it will run at maximum n times.

local function po2(x) return x*2 end
local function iter_po2 = M.iterator(po2, 1, 3)
iter_po2() -- => 2
iter_po2() -- => 4
iter_po2() -- => 8
iter_po2() -- => nil

skip (iter [, n = 1])

Consumes the first n values of a iterator then returns it.

local w = "hello"
local char = string.gmatch(w,'.')
local iter = M.skip(char, 3)
for w in iter do print(w) end -- => 'l', 'o'

n defaults to 1 when not given.

local w = "hello"
local char = string.gmatch(w,'.')
local iter = M.skip(char)
for w in iter do print(w) end -- => 'e', 'l', 'l', 'o'

tabulate (...)

Iterates a given iterator function and returns its values packed in an array.

local text = 'letters'
local chars = string.gmatch(text, '.')
M.tabulate(chars) -- => {'l','e','t','t','e','r','s'}

iterlen (...)

Returns the length of an iterator.

local text = 'letters'
local chars = string.gmatch(text, '.')
M.iterlen(chars) -- => 7

It consumes the iterator itself.

local text = 'lua'
local chars = string.gmatch(text, '.')
M.iterlen(chars) -- => 3
chars() -- => nil

castArray (value)

Casts the passed-in value to an array containing the value itself.

M.castArray(true) -- => {true}
M.castArray(2) -- => {2}

It leaves the given value untouched in case it is already a table.

local t = {1}
print(M.castArray(t) == t) -- => true

flip (f)

Creates a function of f with arguments flipped in reverse order.

local function f(...) return table.concat({...}) end
local flipped = M.flip(f)
flipped('a','b','c') -- => 'cba'

nthArg (n)

Returns a function that gets the nth argument.

local f = M.nthArg(3)
f('a','b','c') -- => 'c'

If n is negative, the nth argument from the end is returned.

local f = M.nthArg(-2)
f('a','b','c') -- => 'b'

unary (f)

Returns a function which accepts up to one argument. It ignores any additional arguments.

local f = M.unary(function (...) return ... end)
f('a') - ==> 'a'
f('a','b','c') -- => 'a'

ary (f [, n = 1])

Aliases: nAry.

Returns a function which accepts up to n args. It ignores any additional arguments.

local f = M.ary(function (...) return ... end, 2)
f(1,2) - ==> 1,2
f(1,2,3,4) -- => 1,2

If n is not given, it defaults to 1.

local f = M.unary(function (...) return ... end)
f('a','b','c') -- => 'a'

noarg (f)

Returns a function with an arity of 0. The new function ignores any arguments passed to it.

local f = M.noarg(function (x) return x or 'default' end)
f(1) -- => 'default'
f(function() end, 3) -- => 'default'

rearg (f, indexes)

Returns a function which runs with arguments arranged according to given indexes.

local f = M.rearg(function (...) return ... end, {5,4,3,2,1})
f('a','b','c','d','e') -- => 'e','d','c','b','a'

over (...)

Creates a function that invokes a set of transforms with the arguments it receives.
One can use use for example to get the tuple of min and max values from a set of values

local minmax = M.over(math.min, math.max)
minmax(5,10,12,4,3) -- => {3,12}

overEvery (...)

Creates a validation function. The returned function checks if all of the given predicates return truthy when invoked with the arguments it receives.

local function alleven(...) 
	for i, v in ipairs({...}) do 
		if v%2~=0 then return false end 
	end 
	return true 
end

local function allpositive(...)
	for i, v in ipairs({...}) do 
		if v < 0 then return false end 
	end 
	return true 	
end

local allok = M.overEvery(alleven, allpositive)

allok(2,4,-1,8) -- => false
allok(10,3,2,6) -- => false
allok(8,4,6,10) -- => true

overSome (...)

Creates a validation function. The returned function checks if any of the given predicates return truthy when invoked with the arguments it receives.

local function alleven(...) 
	for i, v in ipairs({...}) do 
		if v%2~=0 then return false end 
	end 
	return true 
end

local function allpositive(...)
	for i, v in ipairs({...}) do 
		if v < 0 then return false end 
	end 
	return true 	
end

local anyok = M.overSome(alleven,allpositive)

anyok(2,4,-1,8) -- => false
anyok(10,3,2,6) -- => true
anyok(-1,-5,-3) -- => false

overArgs (f, ...)

Creates a function that invokes f with its arguments transformed

local function f(x, y) return x, y end
local function triple(x) retun x*3 end
local function square(x) retun x^2 end
local new_f = M.overArgs(f, triple, square)

new_f(1,2) -- => 3, 4
new_f(10,10) -- => 30, 100

In case the number of arguments is greater than the number of transforms, the remaining args will be left as-is.

local function f(x, y, z) return x, y, z end
local function triple(x) retun x*3 end
local function square(x) retun x^2 end
local new_f = M.overArgs(f, triple, square)

new_f(1,2,3) -- => 3, 4, 3
new_f(10,10,10) -- => 30, 100, 10

converge (f, g, h)

Converges two functions into one.

local function pow2(x) return x*x end
local function pow3(x) return x*x*x end
local function sum(a,b) return a+b end
local poly = M.converge(sum, pow2, pow3)
poly(5) -- => 150 (ie. 5*5 + 5*5*5)

partial (f, ...)

Partially apply a function by filling in any number of its arguments.

local function diff(a, b) return a - b end
local diffFrom20 = M.partial(diff, 20) -- arg 'a' will be 20 by default
diffFrom20(5) -- => 15

The string '_' can be used as a placeholder in the list of arguments to specify an argument that should not be pre-filled, but is rather left open to be supplied at call-time.

local function diff(a, b) return a - b end
local remove5 = M.partial(diff, '_', 5) -- arg 'a' will be given at call-time, but 'b' is set to 5
remove5(20) -- => 15

partialRight (f, ...)

Like M.partial, it partially applies a function by filling in any number of its arguments, but from the right.

local function concat(...) return table.concat({...},',') end
local concat_right = M.partialRight(concat,'a','b','c')
concat_right('d') -- => d,a,b,c

concat_right = M.partialRight(concat,'a','b')
concat_right('c','d') -- => c,d,a,b

concat_right = M.partialRight(concat,'a')
concat_right('b','c','d') -- => b,c,d,a

The string '_', as always, can be used as a placeholder in the list of arguments to specify an argument that should not be pre-filled, but is rather left open to be supplied at call-time. In that case, the first args supplied at runtime will be used to fill the initial list of args while the remaining will be prepended.

local function concat(...) return table.concat({...},',') end
local concat_right = M.partialRight(concat,'a','_','c')
concat_right('d','b') -- => b,a,d,c

concat_right = M.partialRight(concat,'a','b','_')
concat_right('c','d') -- => d,a,b,c

concat_right = M.partialRight(concat,'_','a')
concat_right('b','c','d') -- => c,d,b,a

curry (f [, n_args = 2])

Curries a function. If the given function f takes multiple arguments, it returns another version of f that takes a single argument (the first of the arguments to the original function) and returns a new function that takes the remainder of the arguments and returns the result.

local function sumOf3args(x,y,z) return x + y + z end
local curried_sumOf3args = M.curry(sumOf3args, 3)
sumOf3args(1)(2)(3)) -- => 6
sumOf3args(0)(6)(9)) -- => 15

n_args defaults to 2.

local function product(x,y) return x * y end
local curried_product = M.curry(product)
curried_product(5)(4) -- => 20
curried_product(3)(-5) -- => -15
curried_product(0)(1) -- => 0

time (f [, ...])

Returns the execution time of f (...) in seconds and its results.

local function wait_count(n) 
	local i = 0
	while i < n do i = i + 1 end
	return i
end

local time, i = M.time(wait_count, 1e6) -- => 0.002 1000000
local time, i = M.time(wait_count, 1e7) -- => 0.018 10000000

[⬆]

Object functions

keys (obj)

Collects the names of an object attributes.

M.keys({1,2,3}) -- => "{1,2,3}"
M.keys({x = 0, y = 1}) -- => "{'y','x'}"

values (obj)

Collects the values of an object attributes.

M.values({1,2,3}) -- => "{1,2,3}"
M.values({x = 0, y = 1}) -- => "{1,0}"

path (obj, ...)

Returns the value at a given path in an object.

local entity = {
  pos = {x = 1, y = 2},
  engine = {
    left = {status = 'active', damage = 5},
    right = {status = 'off', damage = 10}
  },
  boost = false
}

M.path(entity,'pos','x') -- => 1
M.path(entity,'pos','y') -- => 2
M.path(entity,'engine','left','status') -- => 'active'
M.path(entity,'engine','right','damage') -- => 10
M.path(entity,'boost') -- => false

spreadPath (obj, ...)

Spreads object under property path onto provided object. It is similar to flattenPath, but removes object under the property path.

local obj = {a = 1, b = 2, c = {d = 3, e = 4, f = {g = 5}}}
M.spreadPath(obj, 'c', 'f')
-- => {a = 1, b = 2, d = 3, e = 4, g = 5, c = {f = {}}}

flattenPath (obj, ...)

Flattens object under property path onto provided object. It is similar to spreadPath, but preserves object under the property path.

local obj = {a = 1, b = 2, c = {d = 3, e = 4, f = {g = 5}}}
M.spreadPath(obj, 'c', 'f')
-- => {a = 1, b = 2, d = 3, e = 4, g = 5, c = {d = 3, e = 4, f = {g = 5}}}

kvpairs (obj)

Converts an object to an array-list of key-value pairs.

local obj = {x = 1, y = 2, z = 3}
M.each(M.kvpairs(obj), function(v,k)
	print(k, table.concat(v,','))	
end)

-- => 1	y,2
-- => 2	x,1
-- => 3	z,3

toObj (kvpairs)

Converts an array list of kvpairs to an object where keys are taken from the 1rst column in the kvpairs sequence, associated with values in the 2nd column.

local list_pairs = {{'x',1},{'y',2},{'z',3}}
obj = M.toObj(list_pairs)

-- => {x = 1, y = 2, z = 3}

invert (obj)

Aliases: mirror.

Switches key-value pairs:

M.invert {'a','b','c'} -- => "{a=1, b=2, c=3}"
M.invert {x = 1, y = 2} -- => "{'x','y'}"

property (key)

Returns a function that will return the key property of any passed-in object.

local who = M.property('name')
local people = {name = 'Henry'}
who(people) -- => 'Henry'

propertyOf (obj)

Returns a function that will return the key property of any passed-in object.

local people = {name = 'Henry'}
print(M.propertyOf(people)('name')) -- => 'Henry'

toBoolean (value)

Converts a given value to a boolean.

M.toBoolean(true) -- => true
M.toBoolean(false) -- => false
M.toBoolean(nil) -- => false
M.toBoolean({}) -- => true
M.toBoolean(1) -- => true

extend (destObj, ...)

Extends a destination object with the properties of some source objects.

M.extend({},{a = 'b', c = 'd'}) -- => "{a = 'b', c = 'd'}"

functions (obj [, recurseMt])

Aliases: methods.

Returns all functions names within an object.

M.functions(coroutine) 
-- => "{'yield','wrap','status','resume','running','create'}"

When given recurseMt, will also include obj metatable's functions.

local mt = {print = print}
local t = {assert = assert}
setmetatable(t, {__index = mt})
M.functions(t, true) -- => "{'assert','print'}"

clone (obj [, shallow])

Clones a given object.

local obj = {1,2,3}
local obj2 = M.clone(obj)
print(obj2 == obj) -- => false
print(M.isEqual(obj2, obj)) -- => true

tap (obj, f)

Invokes a given interceptor function on some object, and then returns the object itself. Useful to tap into method chaining to hook intermediate results. The passed-in interceptor should be prototyped as f(obj,...).

local v = M.chain({1,2,3,4,5,6,7,8,9,10})
  :filter(function(v) return v%2~=0 end) -- retain odd values
  :tap(function(v) print('Max is', M.max(v) end) -- Tap max value 
  :map(function(v) return v^2 end)
  :value() -- =>	 Max is 89

has (obj, key)

Checks if an object has a given attribute.

M.has(_,'has') -- => true
M.has(coroutine,'resume') -- => true
M.has(math,'random') -- => true

pick (obj, ...)

Aliases: choose.

Collects whilelisted properties of a given object.

local object = {a = 1, b = 2, c = 3}
M.pick(object,'a','c') -- => "{a = 1, c = 3}"

omit (obj, ...)

Aliases: drop.

Omits blacklisted properties of a given object.

local object = {a = 1, b = 2, c = 3}
M.omit(object,'a','c') -- => "{b = 2}"

template (obj [, template])

Aliases: defaults.

Applies a template on an object, preserving existing properties.

local obj = {a = 0}
M.template(obj,{a = 1, b = 2, c = 3}) -- => "{a=0, c=3, b=2}"

isEqual (objA, objB [, useMt])

Aliases: compare, M.matches.

Compares objects:

M.isEqual(1,1) -- => true
M.isEqual(true,false) -- => false
M.isEqual(3.14,math.pi) -- => false
M.isEqual({3,4,5},{3,4,{5}}) -- => false

result (obj, method)

Calls an object method, passing it as a first argument the object itself.

M.result('abc','len') -- => 3
M.result({'a','b','c'},table.concat) -- => 'abc'

isTable (t)

Is the given argument an object (i.e a table) ?

M.isTable({}) -- => true
M.isTable(math) -- => true
M.isTable(string) -- => true

isCallable (obj)

Is the given argument callable ?

M.isCallable(print) -- => true
M.isCallable(function() end) -- => true
M.isCallable(setmetatable({},{__index = string}).upper) -- => true
M.isCallable(setmetatable({},{__call = function() return end})) -- => true

isArray (obj)

Is the given argument an array (i.e. a sequence) ?

M.isArray({}) -- => true
M.isArray({1,2,3}) -- => true
M.isArray({'a','b','c'}) -- => true

isIterable (obj)

Checks if the given object is iterable with pairs.

M.isIterable({}) -- => true
M.isIterable(function() end) -- => false
M.isIterable(false) -- => false
M.isIterable(1) -- => false

type (obj)

Extends Lua's type function. It returns the type of the given object and also recognises 'file' userdata

M.type('string') -- => 'string'
M.type(table) -- => 'table'
M.type(function() end) -- => 'function'
M.type(io.open('f','w')) -- => 'file'

isEmpty ([obj])

Is the given argument empty ?

M.isEmpty('') -- => true
M.isEmpty({})  -- => true
M.isEmpty({'a','b','c'}) -- => false

isString (obj)

Is the given argument a string ?

M.isString('') -- => true
M.isString('Hello') -- => false
M.isString({}) -- => false

isFunction (obj)

Is the given argument a function ?

M.isFunction(print) -- => true
M.isFunction(function() end) -- => true
M.isFunction({}) -- => false

isNil (obj)

Is the given argument nil ?

M.isNil(nil) -- => true
M.isNil() -- => true
M.isNil({}) -- => false

isNumber (obj)

Is the given argument a number ?

M.isNumber(math.pi) -- => true
M.isNumber(math.huge) -- => true
M.isNumber(0/0) -- => true
M.isNumber() -- => false

isNaN (obj)

Is the given argument NaN ?

M.isNaN(1) -- => false
M.isNaN(0/0) -- => true

isFinite (obj)

Is the given argument a finite number ?

M.isFinite(99e99) -- => true
M.isFinite(math.pi) -- => true
M.isFinite(math.huge) -- => false
M.isFinite(1/0) -- => false
M.isFinite(0/0) -- => false

isBoolean (obj)

Is the given argument a boolean ?

M.isBoolean(true) -- => true
M.isBoolean(false) -- => true
M.isBoolean(1==1) -- => true
M.isBoolean(print) -- => false

isInteger (obj)

Is the given argument an integer ?

M.isInteger(math.pi) -- => false
M.isInteger(1) -- => true
M.isInteger(-1) -- => true

[⬆]

Chaining

Method chaining (also known as name parameter idiom), is a technique for invoking consecutively method calls in object-oriented style. Each method returns an object, and method calls are chained together. Moses offers chaining for your perusal.

Let's use chaining to get the count of evey single word in some lyrics (case won't matter here).

local lyrics = {
  "I am a lumberjack and I am okay",
  "I sleep all night and I work all day",
  "He is a lumberjack and he is okay",
  "He sleeps all night and he works all day"
}

-- split a text into words
local function words(line)
  local t = {}
  for w in line:gmatch('(%w+)') do t[#t+1] = w end
  return t
end

local stats = M.chain(lyrics)
  :map(words)
  :flatten()
  :countBy(string.lower)
  :value() 

-- => "{
-- =>    sleep = 1, night = 2, works = 1, am = 2, is = 2,
-- =>    he = 2, and = 4, I = 4, he = 2, day = 2, a = 2,
-- =>    work = 1, all = 4, okay = 2
-- =>  }"

For convenience, you can also use M(value) to start chaining methods, instead of M.chain(value).

Note that one can use :value() to unwrap a chained object.

local t = {1,2,3}
print(_(t):value() == t) -- => true

[⬆]

Import

All library functions can be imported in a context using import into a specified context.

local context = {}
M.import(context)

context.each({1,2,3},print)

-- => 1 1
-- => 2 2
-- => 3 3

When no context was provided, it defaults to the current environment, _ENV or _G.

M.import()

each({1,2,3},print)

-- => 1 1
-- => 2 2
-- => 3 3

Passing noConflict argument leaves untouched conflicting keys while importing into the context.

local context = {each = 1}
M.import(context, true)

print(context.each) -- => 1
context.eachi({1,2,3},print)

-- => 1 1
-- => 2 2
-- => 3 3

[⬆]