add signal module

data/scripts/types/signal.lua

@@ -0,0 +1,30 @@
+local util = require "util"
+
+local Signal = {}
+
+Signal.__index = Signal
+
+function Signal:connect(f)
+  util.list_insert_once(self._connections, f)
+end
+
+function Signal:disconnect(f)
+  util.list_remove_value(self._connections, f)
+end
+
+function Signal:emit(...)
+  -- don't care about order
+  for _, v in pairs(self._connections) do
+    v(...)
+  end
+end
+
+function Signal.new()
+  local s = {
+    _connections = {},
+  }
+  
+  return setmetatable(s, Signal)
+end
+
+return Signal

data/scripts/util.lua

@@ -65,4 +65,36 @@ function util.merge(t1, t2, overwrite)
   return t3
 end
 
+---Finds the index of value in list t. If the value does not exist in the list, returns -1.
+---@param t table
+---@param value any
+---@return integer
+function util.list_find(t, value)
+  local idx = -1
+  for i, v in ipairs(t) do
+    if v == value then
+      idx = i
+      break
+    end
+  end
+  return idx
+end
+
+---Removes an element from a list, if it exists. Does nothing if the value doesn't exist.
+---@param t table
+---@param value any
+function util.list_remove_value(t, value)
+  local idx = util.list_find(t, value)
+  if idx ~= -1 then
+    table.remove(t, idx)
+  end
+end
+
+---Inserts value into the list only if it does not exist.
+---@param t table
+---@param value any
+function util.list_insert_once(t, value)
+  if util.list_find(t, value) ~= -1 then return end
+  table.insert(t, value)
+end
 return util