prelude.oops

trait Stream
	head
	tail
	is_empty
	def for_each(f)
		if self.is_empty() then
			[]
		else
			f(self.head())
			self.tail().for_each(f)
		end
	end
	def map(f)
		if self.is_empty() then
			[]
		else
			f(self.head()) :: self.tail().map(f)
		end
	end
	def filter(f)
		if self.is_empty() then
			[]
		else
			let x = self.head() in
				if f(x) then
					x :: self.tail().filter(f)
				else
					self.tail().filter(f)
				end
			end
		end
	end
	def fold(f, i)
		if self.is_empty() then
			i
		else
			self.tail().fold(f, f(i, self.head()))
		end
	end
	def collect()
		if self.is_empty() then
			[]
		else
			self.head() :: self.tail().collect()
		end
	end
end

impl Stream for List
	def is_empty()
		self.length() == 0
	end
end

struct Complex
	re = 0
	im = 0
end
impl for Complex
	def +(other)
		Complex{re: self.re + other.re, im: self.im + other.im}
	end
	def -(other)
		Complex{re: self.re - other.re, im: self.im - other.im}
	end
	def *(other)
		Complex{re: self.re * other.re - self.im * other.im, im: self.re * other.im + self.im * other.re}
	end
	def /(other)
		self * other.conj() * Complex{re: 1 / (other.abs() * other.abs())}
	end
	def conj()
		Complex{re: self.re, im: -self.im}
	end
	def abs()
		sqrt(self.re * self.re + self.im * self.im)
	end
	def to_string()
		"{0} + {1}i".format([self.re, self.im])
	end
end

struct Range
	start
	stop
end
impl Stream for Range
	def head()
		self.start
	end
	def tail()
		Range{start: self.start + 1, stop: self.stop}
	end
	def is_empty()
		self.start > self.stop
	end
	def to_string()
		"{0}..{1}".format([self.start, self.stop])
	end
end