.conf

my_app.complex_list.buzz.type = person
my_app.complex_list.buzz.age  = 25
my_app.complex_list.fido.type = dog
my_app.complex_list.fido.age  = 5

schema.exs

[mappings: [
  "my_app.complex_list.*": [
    to: "my_app.complex_list",
    datatype: [complex: {"my_app.complex_list.*.type", "my_app.complex_list.*.age"}],
    default: []
  ]
  "my_app.complex_list.*.type" [
    to: "my_app.complex_list",
    datatype: :atom,
    default: :undefined
  ],
  "my_app.complex_list.*.age" [
    to: "my_app.complex_list",
    datatype: :integer,
    default: 0
  ]]
 translations: [
   "my_app.complex_list.*": fn
   	_, {name, {type, age}}, nil -> [[name: name, type: type, age: age]]
   	_, {name, {type, age}}, acc -> [[name: name, type: type, age: age] | acc]
  ]]

sys.config

[{my_app,
    complex_list, [
      [{name, buzz},
       {type, person},
       {age, 25],
      [{name, fido},
       {type, dog},
       {age, 5}]
       ]}
]