filter.lua - pipe of applications of Lua methods

filter.lua

-- Usage:
-- filter = require 'filter'
-- command = filter.lower.trim:split(' ')
-- command(input) --> input:lower():trim():split(' ')
-- command(input2) --> input2:lower():trim():split(' ')

local unpack = unpack or table.unpack

local function makeFilter(func, parent_f, parent, method_name)
    return setmetatable({}, {
        __index = function(self, key)
            -- method without arguments
            return makeFilter(function(...)
                local v = func(...)
                return v[key](v)
            end, func, self, key)
        end,

        __call = function(_, self, ...)
            if self == parent then
                -- method with arguments
                local args = {...}
                return makeFilter(function(...)
                    local v = parent_f(...)
                    return v[method_name](v, unpack(args))
                end)
            else
                -- application
                return func(self, ...)
            end
        end,
    })
end

return makeFilter(function(...)
    return ...
end)