Foreign

data Foreign

A type for foreign data.

Foreign data is data from any external unknown or unreliable source, for which it cannot be guaranteed that the runtime representation conforms to that of any particular type.

Suitable applications of Foreign are

• To represent responses from web services
• To integrate with external JavaScript libraries.

data ForeignError

A type for foreign type errors

Constructors

• ForeignError String
• TypeMismatch String String
• ErrorAtIndex Int ForeignError
• ErrorAtProperty String ForeignError

Instances

• Eq ForeignError
• Ord ForeignError
• Show ForeignError

type MultipleErrors = NonEmptyList ForeignError

A type for accumulating multiple ForeignErrors.

type F = Except MultipleErrors

While this alias is not deprecated, it is recommended that one use Except (NonEmptyList ForeignError) directly for all future usages rather than this type alias.

An error monad, used in this library to encode possible failures when dealing with foreign data.

The Alt instance for Except allows us to accumulate errors, unlike Either, which preserves only the last error.

type FT :: (Type -> Type) -> Type -> Typetype FT = ExceptT MultipleErrors

While this alias is not deprecated, it is recommended that one use ExceptT (NonEmptyList ForeignError) directly for all future usages rather than this type alias.

renderForeignError :: ForeignError -> String

unsafeToForeign :: forall a. a -> Foreign

Coerce any value to the a Foreign value.

This is considered unsafe as it's only intended to be used on primitive JavaScript types, rather than PureScript types. Exporting PureScript values via the FFI can be dangerous as they can be mutated by code outside the PureScript program, resulting in difficult to diagnose problems elsewhere.

unsafeFromForeign :: forall a. Foreign -> a

Unsafely coerce a Foreign value.

unsafeReadTagged :: forall m a. Monad m => String -> Foreign -> ExceptT (NonEmptyList ForeignError) m a

Unsafely coerce a Foreign value when the value has a particular tagOf value.

typeOf :: Foreign -> String

Read the Javascript type of a value

tagOf :: Foreign -> String

Read the Javascript tag of a value.

This function wraps the Object.toString method.

isNull :: Foreign -> Boolean

Test whether a foreign value is null

isUndefined :: Foreign -> Boolean

Test whether a foreign value is undefined

isArray :: Foreign -> Boolean

Test whether a foreign value is an array

readString :: forall m. Monad m => Foreign -> ExceptT (NonEmptyList ForeignError) m String

Attempt to coerce a foreign value to a String.

readChar :: forall m. Monad m => Foreign -> ExceptT (NonEmptyList ForeignError) m Char

Attempt to coerce a foreign value to a Char.

readBoolean :: forall m. Monad m => Foreign -> ExceptT (NonEmptyList ForeignError) m Boolean

Attempt to coerce a foreign value to a Boolean.

readNumber :: forall m. Monad m => Foreign -> ExceptT (NonEmptyList ForeignError) m Number

Attempt to coerce a foreign value to a Number.

readInt :: forall m. Monad m => Foreign -> ExceptT (NonEmptyList ForeignError) m Int

Attempt to coerce a foreign value to an Int.

readArray :: forall m. Monad m => Foreign -> ExceptT (NonEmptyList ForeignError) m (Array Foreign)

Attempt to coerce a foreign value to an array.

readNull :: forall m. Monad m => Foreign -> ExceptT (NonEmptyList ForeignError) m (Maybe Foreign)

readUndefined :: forall m. Monad m => Foreign -> ExceptT (NonEmptyList ForeignError) m (Maybe Foreign)

readNullOrUndefined :: forall m. Monad m => Foreign -> ExceptT (NonEmptyList ForeignError) m (Maybe Foreign)

fail :: forall m a. Monad m => ForeignError -> ExceptT (NonEmptyList ForeignError) m a

Throws a failure error in ExceptT (NonEmptyList ForeignError) m.