Merge pull request #35 from natefaubion/row-apply

Add RowApply operator

Author: garyb

src/Type/Row.purs

@@ -12,6 +12,8 @@ module Type.Row
   , class RowListSet
   , class RowListNub
   , class RowListAppend
+  , RowApply
+  , type (+)
   ) where
 
 import Type.Equality (class TypeEquals)
@@ -142,3 +144,16 @@ instance rowListAppendCons
      , TypeEquals (RLProxy (Cons label head out')) (RLProxy out) )
   => RowListAppend (Cons label head tail) rhs out
 
+-- | Type application for rows.
+type RowApply (f :: # Type -> # Type) (a :: # Type) = f a
+
+-- | Applies a type alias of open rows to a set of rows. The primary use case
+-- | this operator is as convenient sugar for combining open rows without
+-- | parentheses.
+-- | ```purescript
+-- | type Rows1 r = (a :: Int, b :: String | r)
+-- | type Rows2 r = (c :: Boolean | r)
+-- | type Rows3 r = (Rows1 + Rows2 + r)
+-- | type Rows4 r = (d :: String | Rows1 + Rows2 + r)
+-- | ```
+infixr 0 type RowApply as +