feat: add f!<interpolated string> macro for Format

src/Lean/Data/FormatMacro.lean

@@ -0,0 +1,18 @@
+#lang lean4
+/-
+Copyright (c) 2020 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Leonardo de Moura
+-/
+import Lean.Data.Format
+namespace Lean
+
+syntax:max "f!" (interpolatedStr term) : term
+
+macro_rules
+| `(f! $interpStr) => do
+  let chunks := interpStr.getArgs
+  let r ← Lean.Syntax.expandInterpolatedStrChunks chunks (fun a b => `($a ++ $b)) (fun a => `(fmt $a))
+  `(($r : Format))
+
+end Lean