gleam/dynamic

Types

pub type Decoder(t) =
  fn(Dynamic) -> Result(t, String)

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

pub fn any(
  from data: Dynamic,
  of decoders: List(fn(Dynamic) -> Result(a, String)),
) -> Result(a, String)

Join multiple decoders into one. When run they will each be tried in turn until one succeeds, or they all fail.

Examples

> import gleam/result
> let bool_or_string = any(_, of: [
>   string,
>   fn(x) { result.map(bool(x), fn(_) { "a bool" }) }
> ])
> bool_or_string(from("ok"))
Ok("ok")

> bool_or_string(from(True))
Ok("a bool")

> bool_or_string(from(1))
Error("Unexpected value")
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`")
pub external fn bit_string(
  from: Dynamic,
) -> Result(BitString, String)

Check to see whether a Dynamic value is a bit_string, and return the bit_string if it is.

Examples

> bit_string(from("Hello")) == bit_string.from_string("Hello")
True

> bit_string(from(123))
Error("Expected a BitString, got `123`")
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`")
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(from(1))

> 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")
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")
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`")
pub external fn from(a) -> Dynamic

Convert any Gleam data into Dynamic data.

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\"`")
pub external fn list(
  from: Dynamic,
) -> Result(List(Dynamic), String)

Check to see whether a Dynamic value is a list, and return the list if it is.

If you wish to decode all the elements in the list use the typed_list instead.

Examples

> list(from(["a", "b", "c"]))
Ok([from("a"), from("b"), from("c")])

> list(1)
Error("Expected an Int, got a binary")
pub external fn map(
  from: Dynamic,
) -> Result(Map(Dynamic, Dynamic), String)

Check to see if the Dynamic value is map.

Examples

> import gleam/map 
> map(from(map.new()))
Ok(map.new())

> map(from(1))
Error("Expected a 2 element tuple, got an int")

> map(from(""))
Error("Expected a map, got a binary")
pub fn option(
  from dynamic: Dynamic,
  of decoder: fn(Dynamic) -> Result(a, String),
) -> Result(Option(a), String)

Check to see if a Dynamic value is an Option of a particular type, and return the Option if it is.

The second argument is a decoder function used to decode the elements of the list. The list is only decoded if all elements in the list can be successfully decoded using this function.

Examples

> option(from("Hello"), string)
Ok(Some("Hello"))

> option(from(atom.from_string("null")), string)
Ok(None)

> option(from(123), string)
Error("Expected a bit_string, got an int")
pub fn result(
  from: Dynamic,
) -> Result(Result(Dynamic, Dynamic), String)

Check to see whether a Dynamic value is a result, and return the result if it is

Examples

> result(from(Ok(1)))
Ok(Ok(from(1)))

> result(from(Error("boom")))
Ok(Error(from("boom")))

> result(from(123))
Error("Expected a 2 element tuple, got an int")
pub 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`")
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`")
pub external fn tuple2(
  from: Dynamic,
) -> Result(tuple(Dynamic, Dynamic), String)

Check to see if the Dynamic value is a 2 element tuple.

If you do not wish to decode all the elements in the tuple use the typed_tuple2 function instead.

Examples

> tuple2(from(tuple(1, 2)))
Ok(tuple(from(1), from(2)))

> tuple2(from(tuple(1, 2)))
Error("Expected a 2 element tuple")

> tuple2(from(""))
Error("Expected a tuple, got a binary")
pub fn typed_list(
  from dynamic: Dynamic,
  of decoder_type: fn(Dynamic) -> Result(a, String),
) -> Result(List(a), String)

Check to see whether a Dynamic value is a list of a particular type, and return the list if it is.

The second argument is a decoder function used to decode the elements of the list. The list is only decoded if all elements in the list can be successfully decoded using this function.

If you do not wish to decode all the elements in the list use the list function instead.

Examples

> typed_list(from(["a", "b", "c"]), of: string)
Ok(["a", "b", "c"])

> typed_list(from([1, 2, 3]), of: string)
Error("Expected an Int, got a binary")

> typed_list(from("ok"), of: string)
Error("Expected a List, got a binary")
pub fn typed_result(
  of dynamic: Dynamic,
  ok decode_ok: fn(Dynamic) -> Result(a, String),
  error decode_error: fn(Dynamic) -> Result(b, String),
) -> Result(Result(a, b), String)

Check to see whether a Dynamic value is a result of a particular type, and return the result if it is

The ok and error arguments are decoders for decoding the Ok and Error values of the result.

Examples

> typed_result(of: from(Ok(1)), ok: int, error: string)
Ok(Ok(1))

> typed_result(of: from(Error("boom")), ok: int, error: string)
Ok(Error("boom"))

> typed_result(of: from(123), ok: int, error: string)
Error("Expected a 2 element tuple, got an int")
pub fn typed_tuple2(
  from tup: Dynamic,
  first decode_first: fn(Dynamic) -> Result(a, String),
  second decode_second: fn(Dynamic) -> Result(b, String),
) -> Result(tuple(a, b), String)

Check to see if the Dynamic value is a 2 element tuple containing two specifically typed elements.

If you wish to decode all the elements in the list use the typed_tuple2 instead.

Examples

> typed_tuple2(from(tuple(1, 2)), int, int)
Ok(tuple(1, 2))

> typed_tuple2(from(tuple(1, 2.0)), int, float)
Ok(tuple(1, 2.0))

> typed_tuple2(from(tuple(1, 2, 3)), int, float)
Error("Expected a 2 element tuple, got a 3 element tuple")

> typed_tuple2(from(""), int, float)
Error("Expected a tuple, got a binary")
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!