ducks.lua

-- Represents a chainable functional stream
-- mutable versions of methods are available under .mutate
function Stream(tbl)
	stream = { values = tbl, mutate = {} }
	function stream.mutate.map(f)
		transform(stream.values, f)
		return stream
	end
	function stream.map(f)
		stream.values = map(stream.values, f)
		return stream
	end
	function stream.tap(f)
		tap(stream.values, f)
		return stream
	end
	function stream.filter(f)
		stream.values = filter(stream.values, f)
		return stream
	end
	function stream.mutate.filter(f)
		filterInplace(stream.values, f)
		return stream
	end
	function stream.dump()
		printtable(stream.values)
		return stream
	end
	function stream.foldLeft(initial, merge)
		return foldLeft(stream.values, initial, merge)
	end
	return stream
end

function foldLeft(tbl, initial, merge)
	local acc = initial
	for k, v in pairs(tbl) do
		acc = merge(acc, v)
	end
	return acc
end

function printtable(tbl)
	for k, v in pairs(tbl) do
		print(k, "->", v)
	end
end

function filter(tbl, f)
	local t = {}
	for k, v in pairs(tbl) do
		if f(v) then t[k] = v end
	end
	return t
end

function filterInplace(tbl, f)
	for k, v in pairs(tbl) do
		if not f(v) then tbl[k] = nil end
	end
end


function tap(tbl, f)
	for k, v in pairs(tbl) do
		f(v)
	end
	return tbl
end

function map(tbl, f)
	local t = {}
	for k,v in pairs(tbl) do
		t[k] = f(v)
	end
	return t
end

function transform(tbl, f)
	for k,v in pairs(tbl) do
		tbl[k] = f(v)
	end
	return tbl
end