list.lua


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--- lam.list

local list = {}
local util = require "util"
local types = require "types"
table.unpack = table.unpack or unpack

list.Null = setmetatable({}, {
		__type = "Null",
		__tostring = function(self) return "()" end,
})

list.isNull =
	function (x)
		return x == list.Null
	end

list.List =
	function (tbl)
		local function tolist (base, items)
			if #items == 0 then return base end
			return tolist (
				types.Cons(table.remove(items), base),
				items
			)
		end
		return tolist(list.Null, tbl)
	end

list.isList =
	function (x)
		if list.isNull(x) then
			return true
		elseif types.isa(x, "Pair") then
			return list.isList(x[2])
		else
			return false
		end
	end

list.fold1 =
	function (fn, seed, lis)
		if list.isNull(lis) then return seed end
		return list.fold1(fn, fn(seed, lis[1]), lis[2])
	end

---
return list