Auto-uncurry n-ary functions.

Implements SIP #897.

1 files changed, 19 insertions, 0 deletions

diff --git a/src/dotty/tools/dotc/ast/Desugar.scala b/src/dotty/tools/dotc/ast/Desugar.scala
index 87694843a..c1083d26d 100644
--- a/src/dotty/tools/dotc/ast/Desugar.scala
+++ b/src/dotty/tools/dotc/ast/Desugar.scala
@@ -588,6 +588,25 @@ object desugar {
     Function(params, Match(selector, cases))
   }
 
+  /** Map n-ary function `(p1, ..., pn) => body` where n != 1 to unary function as follows:
+   *
+   *    x$1 => {
+   *      val p1 = x$1._1
+   *      ...
+   *      val pn = x$1._n
+   *      body
+   *    }
+   */
+  def makeUnaryCaseLambda(params: List[ValDef], body: Tree)(implicit ctx: Context): Tree = {
+    val param = makeSyntheticParameter()
+    def selector(n: Int) = Select(refOfDef(param), nme.selectorName(n))
+    val vdefs =
+      params.zipWithIndex.map{
+        case(param, idx) => cpy.ValDef(param)(rhs = selector(idx))
+      }
+    Function(param :: Nil, Block(vdefs, body))
+  }
+
   /** Add annotation with class `cls` to tree:
    *      tree @cls
    */