Module

Foreign

Package
purescript-foreign
Repository
purescript/purescript-foreign

This module defines types and functions for working with foreign data.

#Foreign Source

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.

#MultipleErrors Source

type MultipleErrors = NonEmptyList ForeignError

A type for accumulating multiple ForeignErrors.

#F Source

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.

#unsafeToForeign Source

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 Source

unsafeFromForeign :: forall a. Foreign -> a

Unsafely coerce a Foreign value.

#unsafeReadTagged Source

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

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

#typeOf Source

typeOf :: Foreign -> String

Read the Javascript type of a value

#tagOf Source

tagOf :: Foreign -> String

Read the Javascript tag of a value.

This function wraps the Object.toString method.

#isNull Source

isNull :: Foreign -> Boolean

Test whether a foreign value is null

#isUndefined Source

isUndefined :: Foreign -> Boolean

Test whether a foreign value is undefined

#isArray Source

isArray :: Foreign -> Boolean

Test whether a foreign value is an array

#readString Source

readString :: Foreign -> F String

Attempt to coerce a foreign value to a String.

#readChar Source

readChar :: Foreign -> F Char

Attempt to coerce a foreign value to a Char.

#readBoolean Source

readBoolean :: Foreign -> F Boolean

Attempt to coerce a foreign value to a Boolean.

#readNumber Source

readNumber :: Foreign -> F Number

Attempt to coerce a foreign value to a Number.

#readInt Source

readInt :: Foreign -> F Int

Attempt to coerce a foreign value to an Int.

#readArray Source

readArray :: Foreign -> F (Array Foreign)

Attempt to coerce a foreign value to an array.

#readNullOrUndefined Source

#fail Source

fail :: forall a. ForeignError -> F a

Throws a failure error in F.