# Pervasion

local include 'util/kind'
local oper \ ktup prefix 40

def extend perv1{op} = {
  def op{a & \a} = each{op, a}
}

def extend perv2{op} = {
  def op{a, b & \b} = each{bind{op,a}, b}
  def op{a, b & \a} = each{{a}=>op{a,b}, a}
  def op{a, b & \a & \b} = each{op, a, b}
}

local def anytup{e, ...t} = if (\e) 1 else anytup{...t}
local def anytup{} = 0

def perv{n & knum{n}} = { def extend _{op} = {
  def op{...t & match{n,tuplen{t}} & anytup{...t}} = {
    def len{e, ...t} = if (\e) tuplen{e} else len{...t}
    def l = len{...t}
    def r{t} = if (\t) t else copy{l,t}
    bind{each,op}{...each{r,t}}
  }
}}
def perv{n==1} = perv1
def perv{n==2} = perv2