added a version of macros.expectLen that takes min/max values

lib/core/macros.nim

@@ -435,6 +435,13 @@ proc expectLen*(n: NimNode, len: int) {.compileTime.} =
   ## macros that check its number of arguments.
   if n.len != len: error("macro expects a node with " & $len & " children", n)
 
+proc expectLen*(n: NimNode, min, max: int) {.compileTime.} =
+  ## checks that `n` has a number of children in the range ``min..max``.
+  ## If this is not the case, compilation aborts with an error message.
+  ## This is useful for writing macros that check its number of arguments.
+  if n.len < min or n.len > max:
+    error("macro expects a node with " & $min & ".." & $max " children", n)
+
 proc newTree*(kind: NimNodeKind,
               children: varargs[NimNode]): NimNode {.compileTime.} =
   ## produces a new node with children.