Missed closing paren in iex, but it still worked

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1

So I’m following along with the Programming Phoenix 1.4 book and I’m at the part where you create the users table and start inserting users into the database (page 63), and I messed up my input in iex like below but it still worked:

iex(2)> Accounts.list_users() |> Enum.map(&(%User{ name: &1.name, username: &1.username}) |> Repo.insert()
...(2)> 
...(2)> )

Notice how I missed the closing ‘)’ around the Enum.map and instead closed it after the Repo.insert.

Yet it still worked and I got the following output:

debug] QUERY OK db=15.1ms decode=19.2ms queue=3.8ms idle=1767.4ms
INSERT INTO "users" ("name","username","inserted_at","updated_at") VALUES ($1,$2,$3,$4) RETURNING "id" ["Jose", "jose_valim", ~N[2021-02-12 01:58:43], ~N[2021-02-12 01:58:43]]
[debug] QUERY OK db=2.4ms queue=1.3ms idle=1893.6ms
INSERT INTO "users" ("name","username","inserted_at","updated_at") VALUES ($1,$2,$3,$4) RETURNING "id" ["Bruce", "redrapids", ~N[2021-02-12 01:58:43], ~N[2021-02-12 01:58:43]]
[debug] QUERY OK db=1.8ms queue=1.0ms idle=897.3ms
INSERT INTO "users" ("name","username","inserted_at","updated_at") VALUES ($1,$2,$3,$4) RETURNING "id" ["Chris", "chrismccord", ~N[2021-02-12 01:58:43], ~N[2021-02-12 01:58:43]]
[
  ok: %Accounts.User{
    __meta__: #Ecto.Schema.Metadata<:loaded, "users">,
    id: 1,
    inserted_at: ~N[2021-02-12 01:58:43],
    name: "Jose",
    updated_at: ~N[2021-02-12 01:58:43],
    username: "jose_valim"
  },
  ok: %Accounts.User{
    __meta__: #Ecto.Schema.Metadata<:loaded, "users">,
    id: 2,
    inserted_at: ~N[2021-02-12 01:58:43],
    name: "Bruce",
    updated_at: ~N[2021-02-12 01:58:43],
    username: "redrapids"
  },
  ok: %Accounts.User{
    __meta__: #Ecto.Schema.Metadata<:loaded, "users">,
    id: 3,
    inserted_at: ~N[2021-02-12 01:58:43],
    name: "Chris",
    updated_at: ~N[2021-02-12 01:58:43],
    username: "chrismccord"
  }
]

Doesn’t it seem odd that it would still work?

2

Now that I’m looking at it harder I’m guessing it’s because it’s considering everything in Enum.map as an anonymous function and thought that was the end of my statement.

3

That is correct. It parsed this as:

Accounts.list_users() |> Enum.map(
  &(
    %User{ name: &1.name, username: &1.username}) |> Repo.insert()
  )
)

The whole of %User{ name: &1.name, username: &1.username}) |> Repo.insert() is the anonymous function, there are no missing parens.

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