GHCJS.Foreign

Basic interop between Haskell and JavaScript.

The principal type here is JSVal, which is a lifted type that contains a JavaScript reference. The JSVal type is parameterized with one phantom type, and GHCJS.Types defines several type synonyms for specific variants.

The code in this module makes no assumptions about 'JSVal a' types. Operations that can result in a JS exception that can kill a Haskell thread are marked unsafe (for example if the JSVal contains a null or undefined value). There are safe variants where the JS exception is propagated as a Haskell exception, so that it can be handled on the Haskell side.

For more specific types, like JSArray or JSBool, the code assumes that the contents of the JSVal actually is a JavaScript array or bool value. If it contains an unexpected value, the code can result in exceptions that kill the Haskell thread, even for functions not marked unsafe.

The code makes use of `foreign import javascript', enabled with the JavaScriptFFI extension, available since GHC 7.8. There are three different safety levels:

• unsafe: The imported code is run directly. returning an incorrectly typed value leads to undefined behaviour. JavaScript exceptions in the foreign code kill the Haskell thread.
• safe: Returned values are replaced with a default value if they have the wrong type. JavaScript exceptions are caught and propagated as Haskell exceptions (JSException), so they can be handled with the standard Control.Exception machinery.
• interruptible: The import is asynchronous. The calling Haskell thread sleeps until the foreign code calls the `$c` JavaScript function with the result. The thread is in interruptible state while blocked, so it can receive asynchronous exceptions.

Unlike the FFI for native code, it's safe to call back into Haskell (`h$run`, `h$runSync`) from foreign code in any of the safety levels. Since JavaScript is single threaded, no Haskell threads can run while the foreign code is running.

Documentation

jsTrue :: JSVal

jsFalse :: JSVal

jsNull :: JSVal

toJSBool :: Bool -> JSVal

fromJSBool :: JSVal -> Bool

jsUndefined :: JSVal

isTruthy :: JSVal -> Bool

isNull :: JSVal -> Bool

isUndefined :: JSVal -> Bool

isObject :: JSVal -> Bool

isFunction :: JSVal -> Bool

isString :: JSVal -> Bool

isBoolean :: JSVal -> Bool

isSymbol :: JSVal -> Bool

isNumber :: JSVal -> Bool

jsTypeOf :: JSVal -> JSType

data JSType

Constructors

Undefined

Object

Boolean

Number

String

Symbol

Function

Other

implementation dependent

Instances

Enum JSType

Defined in GHCJS.Foreign.Internal

Methods

succ :: JSType -> JSType

pred :: JSType -> JSType

toEnum :: Int -> JSType

fromEnum :: JSType -> Int

enumFrom :: JSType -> [JSType]

enumFromThen :: JSType -> JSType -> [JSType]

enumFromTo :: JSType -> JSType -> [JSType]

enumFromThenTo :: JSType -> JSType -> JSType -> [JSType]

Eq JSType

Defined in GHCJS.Foreign.Internal

Methods

(==) :: JSType -> JSType -> Bool

(/=) :: JSType -> JSType -> Bool

Ord JSType

Defined in GHCJS.Foreign.Internal

Methods

compare :: JSType -> JSType -> Ordering

(<) :: JSType -> JSType -> Bool

(<=) :: JSType -> JSType -> Bool

(>) :: JSType -> JSType -> Bool

(>=) :: JSType -> JSType -> Bool

max :: JSType -> JSType -> JSType

min :: JSType -> JSType -> JSType

Show JSType

Defined in GHCJS.Foreign.Internal

Methods

showsPrec :: Int -> JSType -> ShowS

show :: JSType -> String

showList :: [JSType] -> ShowS

jsonTypeOf :: JSVal -> JSONType

data JSONType

Constructors

JSONNull

JSONInteger

JSONFloat

JSONBool

JSONString

JSONArray

JSONObject

Instances

Enum JSONType

Defined in GHCJS.Foreign.Internal

Methods

succ :: JSONType -> JSONType

pred :: JSONType -> JSONType

toEnum :: Int -> JSONType

fromEnum :: JSONType -> Int

enumFrom :: JSONType -> [JSONType]

enumFromThen :: JSONType -> JSONType -> [JSONType]

enumFromTo :: JSONType -> JSONType -> [JSONType]

enumFromThenTo :: JSONType -> JSONType -> JSONType -> [JSONType]

Eq JSONType

Defined in GHCJS.Foreign.Internal

Methods

(==) :: JSONType -> JSONType -> Bool

(/=) :: JSONType -> JSONType -> Bool

Ord JSONType

Defined in GHCJS.Foreign.Internal

Methods

compare :: JSONType -> JSONType -> Ordering

(<) :: JSONType -> JSONType -> Bool

(<=) :: JSONType -> JSONType -> Bool

(>) :: JSONType -> JSONType -> Bool

(>=) :: JSONType -> JSONType -> Bool

max :: JSONType -> JSONType -> JSONType

min :: JSONType -> JSONType -> JSONType

Show JSONType

Defined in GHCJS.Foreign.Internal

Methods

showsPrec :: Int -> JSONType -> ShowS

show :: JSONType -> String

showList :: [JSONType] -> ShowS