Qlc

Qlc is implementation erlang's qlc interface by elixir.

The qlc module implements a query interface to QLC tables. Typical QLC tables are ETS, Dets, and Mnesia tables. There is also support for user defined tables, see the Implementing a QLC table section. A query is stated using Query List Comprehensions (QLCs).

for more information, see erlang reference manual

build

1. find sure qlc.erl in 'stdlib/src'.
2. mix test
3. mix docs (option)

feature

Allow erlang style list comprehensions for List, ets, Dets, Mnesia QLC tables.

example

iex> require Qlc
iex> list = [a: 1,b: 2,c: 3]
iex> qlc_handle = Qlc.q("[X || X = {K,V} <- L, K =/= Item]", 
...>        [L: list, Item: :b])
...> Qlc.e(qlc_handle)
[a: 1, c: 3]

Qlc.Record.defrecord/2 defines the bang!/2 macro expanding to 'element(index, record)', for treating record element in qlc query.

Examples

iex(1)> require Qlc.Record
Qlc.Record
iex(2)> require Qlc
Qlc
iex(3)> defmodule A do
...(3)> Qlc.Record.defrecord(:item, [id: nil, name: nil, age: nil])
...(3)> end
{:module, A,
 <<70, 79, 82, 49, 0, 0, 10, 48, 66, 69, ...>>, {:item!, 2}}
iex(4)> require A
A
iex(5)> import A
A
iex(6)> item()
{:item, nil, nil, nil}
iex(7)> item([id: 1, name: :foo, age: 10])
{:item, 1, :foo, 10}
iex(8)> item!({:item, 1, :foo, 10}, :age)
[
  32,
  101,
  108,
  101,
  109,
  101,
  110,
  116,
  40,
  '4',
  44,
  32,
  [[123, ['item', 44, '1', 44, 'foo', 44, '10'], 125]],
  41,
  32
]
iex(9)> item!({:item, 1, :foo, 10}, :age)|>List.flatten()
' element(4, {item,1,foo,10}) '
iex(10)> list = [item(id: 1, name: :a, age: 1), 
...(10)>         item(id: 2, name: :b, age: 10), 
...(10)>         item(id: 3, name: :c, age: 20)]
[{:item, 1, :a, 1}, {:item, 2, :b, 10}, {:item, 3, :c, 20}]
iex(11)> Qlc.q("[ X || X <- L, (N = #{item!(X, :name)}) =:= Name]", 
...(11)>      [L: list, Name: :b]) |>
...(11)> Qlc.sort(order: :descending) |>
...(11)> Qlc.e()
[{:item, 2, :b, 10}]

## Cannot use bang!/2 macro with variable, can use literal only

iex(12)> b = item([id: 1, name: :foo, age: 10])
{:item, 1, :foo, 10}
iex(13)> item!(b, :name)
warning: variable "b" does not exist and is being expanded to "b()", please use parentheses to remove the ambiguity or change the variable name
iex(14)> 

licenses

MIT licenses.