gleam/dynamic
Types
Dynamic
Dynamic data is data that we don"t know the type of yet.
We likely get data like this from interop with Erlang, or from
IO with the outside world.
pub external type Dynamic
Functions
atom
pub external fn atom(from: Dynamic) -> Result(atom.Atom, String)
Check to see whether a Dynamic value is an atom, and return the atom if it is.
Examples
> import gleam/atom
> atom(from(atom.create_from_string("hello")))
OK("hello")
> atom(from(123))
Error("Expected an Atom, got `123`")
bool
pub external fn bool(from: Dynamic) -> Result(Bool, String)
Check to see whether a Dynamic value is an bool, and return the bool if it is.
Examples
> bool(from(True))
Ok(True)
> bool(from(123))
Error("Expected a Bool, got `123`")
element
pub external fn element( from: Dynamic, position: Int, ) -> Result(Dynamic, String)
Check to see if the Dynamic value is a tuple large enough to have a certain index, and return the value of that index if it is.
Examples
> element(from(tuple(1, 2)), 0)
Ok(Dynamic)
> element(from(tuple(1, 2)), 2)
Error("Expected a tuple of at least 3 size, got a tuple of 2 size")
> element(from(""), 2)
Error("Expected a Tuple, got a binary")
field
pub external fn field( from: Dynamic, named: a, ) -> Result(Dynamic, String)
Check to see if a Dynamic value is a map with a specific field, and return the value of the field if it is.
This will not succeed on a record.
Examples
> import gleam/map
> field(from(map.new("Hello", "World")), "Hello")
Ok(Dynamic)
> field(from(123), "Hello")
Error("Expected a map with key `\"Hello\"`, got an Int")
float
pub external fn float(from: Dynamic) -> Result(Float, String)
Check to see whether a Dynamic value is an float, and return the float if it is.
Examples
> float(from(2.0))
Ok(2.0)
> float(from(123))
Error("Expected a Float, got `123`")
int
pub external fn int(from: Dynamic) -> Result(Int, String)
Check to see whether a Dynamic value is an int, and return the int if it is.
Examples
> int(from(123))
Ok(123)
> int(from("Hello"))
Error("Expected an Int, got `\"Hello World\"`")
list
pub fn list( from dynamic: Dynamic, containing decoder_type: fn(Dynamic) -> Result(a, String), ) -> Result(List(a), String)
Check to see whether a Dynamic value is a list, and return the list if it is.
Examples
> list(from(["a", "b", "c"]), string)
Ok(["a", "b", "c"])
> list(from([1, 2, 3]), string)
Error("Expected an Int, got a binary")
> list(from("ok"), string)
Error("Expected a List, got a binary")
string
pub external fn string(from: Dynamic) -> Result(String, String)
Check to see whether a Dynamic value is a string, and return the string if it is.
Examples
> string(from("Hello"))
Ok("Hello")
> string(from(123))
Error("Expected a String, got `123`")
thunk
pub external fn thunk( from: Dynamic, ) -> Result(fn() -> Dynamic, String)
Check to see whether a Dynamic value is a function that takes no arguments, and return the function if it is.
Examples
> import gleam/result
> let f = fn() { 1 }
> thunk(from(f)) |> result.is_ok
True
> thunk(from(123))
Error("Expected a zero arity function, got `123`")
unsafe_coerce
pub external fn unsafe_coerce(Dynamic) -> a
Unsafely cast a Dynamic value into any other type.
This is an escape hatch for the type system that may be useful when wrapping native Erlang APIs. It is to be used as a last measure only!
If you can avoid using this function, do!