--[[
Functional programming primitives that are occasionally useful

This is not a complete set of primitives, I make them when I need them. Anywhere I use these 
heavily (where someone unfamiliar with the functional paradigm might get confused)
I have tried to add comments above or below explaining what it does.
]]
local fn = {}

--Returns a function that "stores" the arguments this function was called with
--For example
--[[
local hiprint = fn.curry(print,"[hi]")
hiprint("world") -- calls print("[hi]","world"), prints "[hi] world"
]]
function fn.curry(func,...)
	local args = {...}
	return function(...)
		local nargs = {}
		for k,v in pairs(args) do nargs[k] = v end
		for k,v in pairs({...}) do
			nargs[#nargs + 1] = v
		end
		func(table.unpack(nargs))
	end
end

--Returns a function that calls all functions starting with the rightmost function
--and calling the "next" function with the returns of the previous function.
--The first function can be called with any arguments like normal
--Anything returned from the last function is returned "out" of this function.
--Example:
--
--local fn = require("fn")
--local printf = fn.compose(print,string.format)
--printf("This is %s shit","funky") --prints "This is some funky shit"
function fn.compose(...)
	local nargs = {...}
	local lastresult
	return function(...)
		lastresult = {...}
		for n = #nargs, 1, -1 do
			lastresult = {nargs[n](table.unpack(lastresult))}
		end
		return table.unpack(lastresult)
	end
end

--Returns a function that applies the given function on a table called with it.
--Example:
--
--local fn = require("fn")
--local add_five = fn.map(function(e) return e + 5 end)
--add_five({1,4,9}) --Returns a table {6,10,14}
function fn.map(func)
	return function(tbl)
		local ret = {}
		for k,v in pairs(tbl) do
			ret[k] = func(v)
		end
		return ret
	end
end

--Returns a function that removes anything NOT matching the given function
--Example:
--
--local fn = require("fn")
--local important_skills = fn.filter(function(e) return e > 10 end)
--local usable_skills = imporant_skills({
--	["wood cutting"] = 5,
--	["mining"] = 21,
--	["fighting"] = 12,
--	["fishing"] = 10,
--})
--for k,v in pairs(usable_skills) print(k,":",v) end --prints:
--mining : 21
--fighting : 12
function fn.filter(func)
	return function(tbl)
		local ret = {}
		for k,v in pairs(tbl) do
			if not func(v) then
				ret[k] = v
			end
		end
		return ret
	end
end

--Get the keys of a table in an array
function fn.keys(tbl)
	local ret = {}
	for k,v in pairs(tbl) do
		table.insert(ret,k)
	end
	return ret
end

--Get the values of a table in an array
function fn.values(tbl)
	local ret = {}
	for k,v in pairs(tbl) do
		table.insert(ret,v)
	end
	return ret
end

--Reverses an array
function fn.reverse(tbl)
	local ret = {}
	local len = #tbl
	for i = 1,len do
		ret[len - i + 1] = tbl[i]
	end
	return ret
end


return fn