Ink.jl

module Ink

mutable struct Thunk
  f::Function
  result::Any
  sub::Vector{Thunk}
  sup::Vector{Thunk}
  clean::Bool
end

thunk(f) = Thunk(f, nothing, [], [], false)

function add_edge(sup::Thunk, sub::Thunk)
  push!(sup.sub, sub)
  push!(sub.sup, sup)
end

function del_edge(sup::Thunk, sub::Thunk)
  filter!(sub₁ -> sub₁ != sub, sup.sub)
  filter!(sup₁ -> sup₁ != sup, sub.sup)
end

function compute!(t::Thunk)
  if t.clean
    t.result
  else
    for s in t.sub
      del_edge(s, t)
    end
    t.clean = true
    t.result = t.f(t)
    compute!(t)
  end
end

function dirty!(t::Thunk)
  if t.clean
    t.clean = false
    for s in t.sup
      dirty!(s)
    end
  end
end

ref(v) = Thunk(compute!, v, [], [], true)

function set!(t::Thunk, v::Any)
  t.result = v
  dirty!(t)
end

macro read(t)
  self = esc(:self)
  t = esc(t)
  quote
    add_edge($self, $t)
    compute!($t)
  end
end

macro thunk(body)
  self = esc(:self)
  body = esc(body)
  quote
    thunk(($self) -> $body)
  end
end

export @thunk, @read, ref, set!, compute!

end