Lua 函数链功能

函数链

http://lua-users.org/wiki/FiltersSourcesAndSinks

A chain is a function that combines the effect of two (or more) other functions, but whose interface is indistinguishable from the interface of one of its components. Thus, a chained filter can be used wherever an atomic filter can be used. However, its effect on data is the combined effect of its component filters. Note that, as a consequence, chains can be chained themselves to create arbitrarily complex operations that can be used just like atomic operations.

DEMO

local function chain2(f1, f2)
  return function(chunk)
    local ret = f2(f1(chunk))
    if chunk then return ret
    else return ret .. f2() end
  end
end

local filter = {}
function filter.chain(...)
  local f = arg[1]
  for i = 2, table.getn(arg) do
    f = chain2(f, arg[i])
  end
  return f
end


local function addOne( subject )
    return subject + 1
end

local function minOne( subject )
    return subject - 1
end

local nullFunc = filter.chain(addOne, minOne)

local result = nullFunc(56)
print(result)


local nullFunc_1 = filter.chain(minOne, addOne)
local result = nullFunc_1(6)
print(result)

扩展

Filters can be seen as internal nodes in a network through which data flows, potentially being transformed along its way. Chains connect these nodes together. To complete the picture, we need sources and sinks as initial and final nodes of the network, respectively. Less abstractly, a source is a function that produces new data every time it is called. On the other hand, sinks are functions that give a final destination to the data they receive. Naturally, sources and sinks can be chained with filters.

Finally, filters, chains, sources, and sinks are all passive entities: they need to be repeatedly called in order for something to happen. Pumps provide the driving force that pushes data through the network, from a source to a sink.

http://lua-users.org/wiki/FiltersSourcesAndSinks