add rename and Builder.rename (#18)

src/Data/Record.purs

@@ -4,6 +4,7 @@ module Data.Record
   , modify
   , insert
   , delete
+  , rename
   , equal
   , class EqualFields
   , equalFields
@@ -114,6 +115,32 @@ delete
   -> Record r1
 delete l r = runFn2 unsafeDeleteFn (reflectSymbol l) r
 
+-- | Rename a property for a label which is specified using a value-level proxy for
+-- | a type-level string.
+-- |
+-- | Note that the type of the resulting row must _lack_ the specified property.
+-- | Since duplicate labels are allowed, this is checked with a type class constraint.
+-- |
+-- | For example:
+-- |
+-- | ```purescript
+-- | rename (SProxy :: SProxy "x") (SProxy :: SProxy "y")
+-- |   :: forall a r. RowLacks "x" r => RowLacks "y" r => { x :: a | r} -> { y :: a | r}
+-- | ```
+rename :: forall prev next ty input inter output
+   . IsSymbol prev
+  => IsSymbol next
+  => RowCons prev ty inter input
+  => RowLacks prev inter
+  => RowCons next ty inter output
+  => RowLacks next inter
+  => SProxy prev
+  -> SProxy next
+  -> Record input
+  -> Record output
+rename prev next record =
+  insert next (get prev record) (delete prev record :: Record inter)
+
 -- | Check two records of the same type for equality.
 equal
   :: forall r rs

src/Data/Record/Builder.js

@@ -26,6 +26,16 @@ exports.unsafeDelete = function(l) {
   };
 };
 
+exports.unsafeRename = function(l1) {
+  return function (l2) {
+    return function (rec) {
+      rec[l2] = rec[l1];
+      delete rec[l1];
+      return rec;
+    };
+  };
+};
+
 exports.unsafeMerge = function(r1) {
   return function(r2) {
     var copy = {};

src/Data/Record/Builder.purs

@@ -3,6 +3,7 @@ module Data.Record.Builder
   , build
   , insert
   , delete
+  , rename
   , merge
   ) where
 
@@ -14,6 +15,7 @@ import Type.Row (class RowLacks)
 foreign import copyRecord :: forall r1. Record r1 -> Record r1
 foreign import unsafeInsert :: forall a r1 r2. String -> a -> Record r1 -> Record r2
 foreign import unsafeDelete :: forall r1 r2. String -> Record r1 -> Record r2
+foreign import unsafeRename :: forall r1 r2. String -> String -> Record r1 -> Record r2
 foreign import unsafeMerge :: forall r1 r2 r3. Record r1 -> Record r2 -> Record r3
 
 -- | A `Builder` can be used to `build` a record by incrementally adding
@@ -57,6 +59,19 @@ delete
    -> Builder (Record r2) (Record r1)
 delete l = Builder \r2 -> unsafeDelete (reflectSymbol l) r2
 
+-- | Build by renaming an existing field.
+rename :: forall l1 l2 a r1 r2 r3
+   . IsSymbol l1
+  => IsSymbol l2
+  => RowCons l1 a r2 r1
+  => RowLacks l1 r2
+  => RowCons l2 a r2 r3
+  => RowLacks l2 r2
+  => SProxy l1
+  -> SProxy l2
+  -> Builder (Record r1) (Record r3)
+rename l1 l2 = Builder \r1 -> unsafeRename (reflectSymbol l1) (reflectSymbol l2) r1
+
 -- | Build by merging existing fields from another record.
 merge
   :: forall r1 r2 r3

test/Main.purs

@@ -3,7 +3,7 @@ module Test.Main where
 import Prelude
 
 import Control.Monad.Eff (Eff)
-import Data.Record (delete, get, insert, modify, set, equal)
+import Data.Record (delete, equal, get, insert, modify, rename, set)
 import Data.Record.Builder as Builder
 import Data.Record.ST (pokeSTRecord, pureSTRecord, thawSTRecord)
 import Data.Record.Unsafe (unsafeHas)
@@ -14,6 +14,7 @@ main :: Eff (assert :: ASSERT) Unit
 main = do
   let x = SProxy :: SProxy "x"
       y = SProxy :: SProxy "y"
+      z = SProxy :: SProxy "z"
 
   assert' "insert, get" $
     get x (insert x 42 {}) == 42
@@ -25,6 +26,8 @@ main = do
     get x (modify x (_ + 1) (set x 0 { x: 42 })) == 1
   assert' "delete, get" $
     get x (delete y { x: 42, y: 1337 }) == 42
+  assert' "rename" $
+    get y (rename x y { x: 42 }) == 42
   assert' "equal" $
     equal { a: 1, b: "b", c: true } { a: 1, b: "b", c: true }
   assert' "equal2" $
@@ -42,10 +45,11 @@ main = do
 
   assert' "pokeSTRecord" $
     stTest1.x == 42 && stTest1.y == "testing"
-    
+
   let testBuilder = Builder.build (Builder.insert x 42
                                   >>> Builder.merge { y: true, z: "testing" }
-                                  >>> Builder.delete y) {}
+                                  >>> Builder.delete y
+                                  >>> Builder.rename z y) {}
 
   assert' "Data.Record.Builder" $
-    testBuilder.x == 42 && testBuilder.z == "testing"
+    testBuilder.x == 42 && testBuilder.y == "testing"