Atom is a special string-like data-type that is most commonly used for interfacing with code written in other BEAM languages such as Erlang and Elixir. It is preferable to define your own custom types to use instead of atoms where possible.

Atoms are not used much in typical Gleam code!

Creating atoms

We can create atoms with the the create_from_string function, though we must be careful when doing so as atoms are never garbage collected. If we create too many atoms (for example, if we convert user input into atoms) we may hit the max limit of atoms and cause the virtual machine to crash.

pub type Atom

An error returned when no atom is found in the virtual machine’s atom table for a given string when calling the from_string function.

pub type FromStringError {


  • AtomNotLoaded


pub fn create_from_string(a: String) -> Atom

Creates an atom from a string, inserting a new value into the virtual machine’s atom table if an atom does not already exist for the given string.

We must be careful when using this function as there is a limit to the number of atom that can fit in the virtual machine’s atom table. Never convert user input into atoms as filling the atom table will cause the virtual machine to crash!

pub fn from_dynamic(
  from from: Dynamic,
) -> Result(Atom, List(DecodeError))

Checks to see whether a Dynamic value is an atom, and return the atom if it is.


import gleam/dynamic from_dynamic(dynamic.from(create_from_string(“hello”))) Ok(create_from_string(“hello”))

from_dynamic(dynamic.from(123)) Error([DecodeError(expected: “Atom”, found: “Int”, path: [])])

pub fn from_string(a: String) -> Result(Atom, FromStringError)

Finds an existing Atom for the given String.

If no atom is found in the virtual machine’s atom table for the String then an error is returned.


from_string(“ok”) Ok(create_from_string(“ok”))

from_string(“some_new_atom”) Error(AtomNotLoaded)

pub fn to_string(a: Atom) -> String

Returns a String corresponding to the text representation of the given Atom.


let ok_atom = create_from_string(“ok”) to_string(ok_atom) “ok”

Search Document