Today I Learned

A Hashrocket project

Referencing Values In IEx's History

Each time we execute a statement in an iex session, the counter is incremented. These numbers are references to the history of the session. We can use these references to refer to previously executed values using v/1. This is particularly handy for multi-line statements or when we forget to bind to the result of some function.

Consider the following iex session:

iex(1)> :one
:one
iex(2)> 1 + 1
2
iex(3)> "three" |> String.to_atom()
:three

If we execute v() on its own, it is the same as v(-1) in that it will give us the latest value in the history.

iex(4)> v()
:three

Providing any positive number will refer to the references we see next to each statement.

iex(5)> v(1)
:one

Negative numbers, as we saw with v(-1), will count backwards in the history from where we are.

iex(6)> v(-4)
2

See h v for more details.

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