Add functions to convert to / from a Promise to a LazyPromise (#12)

Author: thomashoneyman

CHANGELOG.md

@@ -7,6 +7,7 @@ Notable changes to this project are documented in this file. The format is based
 Breaking changes:
 
 New features:
+- Added `toPromise` and `fromPromise` helper functions to the `LazyPromise` module for convenient transformations between the `Promise` and `LazyPromise` types (#12 by @thomashoneyman)
 
 Bugfixes:
 

src/Web/Promise/Lazy.purs

@@ -7,7 +7,7 @@ import Data.Traversable (traverse)
 import Effect (Effect)
 import Effect.Class (class MonadEffect)
 import Effect.Uncurried (mkEffectFn1, mkEffectFn2, runEffectFn1, runEffectFn2)
-import Web.Promise (Executor, Rejection)
+import Web.Promise (class Flatten, Executor, Rejection)
 import Web.Promise.Internal as P
 
 -- | A trivial box that adds a layer between promises to prevent automatic flattening.
@@ -68,3 +68,9 @@ race :: forall a. Array (LazyPromise a) -> LazyPromise a
 race as = LazyPromise do
   as' <- traverse (\(LazyPromise a) -> a) as
   runEffectFn1 P.race as'
+
+fromPromise :: forall a. Effect (P.Promise a) -> LazyPromise a
+fromPromise p = LazyPromise $ runEffectFn2 P.then_ (mkEffectFn1 (pure <<< P.resolve <<< Box)) =<< p
+
+toPromise :: forall a b. Flatten a b => LazyPromise a -> Effect (P.Promise b)
+toPromise (LazyPromise p) = runEffectFn2 P.then_ (mkEffectFn1 \(Box b) -> pure (P.resolve b)) =<< p