Foreign

data Foreign :: Type

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

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.

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 a. String -> Foreign -> F 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 :: Foreign -> F String

Attempt to coerce a foreign value to a String.

readChar :: Foreign -> F Char

Attempt to coerce a foreign value to a Char.

readBoolean :: Foreign -> F Boolean

Attempt to coerce a foreign value to a Boolean.

readNumber :: Foreign -> F Number

Attempt to coerce a foreign value to a Number.

readInt :: Foreign -> F Int

Attempt to coerce a foreign value to an Int.

readArray :: Foreign -> F (Array Foreign)

Attempt to coerce a foreign value to an array.

readNull :: Foreign -> F (Maybe Foreign)

readUndefined :: Foreign -> F (Maybe Foreign)

readNullOrUndefined :: Foreign -> F (Maybe Foreign)

fail :: forall a. ForeignError -> F a

Throws a failure error in F.