feat: add LeanExt.lean and ParserDescr type

src/Init/Lean/Data/Name.lean

@@ -4,7 +4,7 @@ Released under Apache 2.0 license as described in the file LICENSE.
 Author: Leonardo de Moura
 -/
 prelude
-import Init.Data.String.Basic
+import Init.LeanExt
 import Init.Coe
 import Init.Data.UInt
 import Init.Data.ToString
@@ -14,11 +14,6 @@ import Init.Data.RBTree
 
 namespace Lean
 
-inductive Name
-| anonymous : Name
-| str : Name → String → USize → Name
-| num : Name → Nat → USize → Name
-
 instance Name.inhabited : Inhabited Name :=
 ⟨Name.anonymous⟩
 

src/Init/LeanExt.lean

@@ -0,0 +1,43 @@
+/-
+Copyright (c) 2019 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Leonardo de Moura
+-/
+prelude
+import Init.Data.String.Basic
+import Init.Data.UInt
+
+namespace Lean
+/-
+Basic Lean types used to implement basic extensions.
+Note that this file is part of the Lean `Init` library instead of
+`Lean` actual implementation.
+The idea is to allow users to implement simple parsers, macros and tactics
+without importing the whole `Lean` module.
+It also allow us to use extensions to develop the `Init` library.
+-/
+
+/- Hierarchical names -/
+inductive Name
+| anonymous : Name
+| str : Name → String → USize → Name
+| num : Name → Nat → USize → Name
+
+/-
+  Small DSL for describing parsers. We implement an interpreter for it
+  at `Parser.lean` -/
+inductive ParserDescr
+| andthen       : ParserDescr → ParserDescr → ParserDescr
+| orelse        : ParserDescr → ParserDescr → ParserDescr
+| optional      : ParserDescr → ParserDescr
+| lookahead     : ParserDescr → ParserDescr
+| try           : ParserDescr → ParserDescr
+| many          : ParserDescr → ParserDescr
+| many1         : ParserDescr → ParserDescr
+| sepBy         : ParserDescr → ParserDescr → ParserDescr
+| sepBy1        : ParserDescr → ParserDescr → ParserDescr
+| symbol        : String → Nat → ParserDescr
+| unicodeSymbol : String → String → Nat → ParserDescr
+| parser        : Name → ParserDescr
+
+end Lean