A thing for working with JSUnions by guarding members and otherwise creating and extracting members.
See the tests for all of the examples.
Further Reading
You may be interested in reading my blog posts accompanying this library explaining some motivations and methods for implemenation:
-
Matching on JS Union members with Row Types (Handling JS Unions cont.): https://qiita.com/kimagure/items/7a0d1675522c09b4bcb6
-
Handling JS Unions with Row Types: https://qiita.com/kimagure/items/141423771ad1f5a84425
Examples:
Guarding a two-member union and extracting out the remaining singleton
type TestUnion = H.JSUnion
( name :: String
, count :: Int
)
nameP = SProxy :: SProxy "name"
countP = SProxy :: SProxy "count"
countGuard :: H.UnsafeGuardFor "count" Int
countGuard =
H.UnsafeGuardFor
$ isRight
<<< runExcept
<<< readInt
nameGuard :: H.UnsafeGuardFor "name" String
nameGuard =
H.UnsafeGuardFor
$ isRight
<<< runExcept
<<< readString
-- ...
T.test "unsafeGuardMember 1" do
let
(union :: TestUnion) = H.fromMember nameP "banana"
guarded = H.unsafeGuardMember countGuard union
case guarded of
Right e ->
T.failure "incorrect branch from JSUnion"
Left singleton -> do
let value = H.unsafeExtractSingleton singleton
Assert.equal value "banana"Matching on union members, with a Nothing returned for no matches
-- ...
T.test "matchMembers 1" do
let
(union :: TestUnion) = H.fromMember countP 1
match = H.matchJSUnion
{ count: Tuple countGuard show
, name: Tuple nameGuard identity
}
union
case match of
Just value -> do
Assert.equal value "1"
Nothing ->
T.failure "incorrect result from matchJSUnion"
T.test "matchMembers 2" do
let
(union :: TestUnion) = unsafeCoerce { crap: "some bullshit from JS" }
match = H.matchJSUnion
{ count: Tuple countGuard show
, name: Tuple nameGuard identity
}
union
case match of
Just value -> do
T.failure "incorrect result from matchJSUnion"
Nothing ->
T.successUsing Chalk.js properties as both functions and objects
chalkMain :: Effect Unit
chalkMain = do
let
fnP = SProxy :: SProxy "fn"
objP = SProxy :: SProxy "obj"
blueFn = H.unsafeCoerceMember fnP chalk.blue
blueObj = H.unsafeCoerceMember objP chalk.blue
log $ blueFn "blue text"
log $ blueObj.bgYellow "yellow background blue text"
foreign import chalk
:: { blue
:: H.JSUnion
( fn :: String -> String
, obj :: { bgYellow :: String -> String }
)
}