Integrate build and documentation of Ltac2

Since Ltac2 cannot be put under the stdlib logical root (some file names
would clash), we move it to the `user-contrib` directory, to avoid adding
another hardcoded path in `coqinit.ml`, following a suggestion by @ejgallego.

Thanks to @Zimmi48 for the thorough documentation review and the
numerous suggestions.

1 files changed, 36 insertions, 0 deletions

diff --git a/user-contrib/Ltac2/Ltac1.v b/user-contrib/Ltac2/Ltac1.v
new file mode 100644
index 0000000000..c4e0b606d0
--- /dev/null
+++ b/user-contrib/Ltac2/Ltac1.v
@@ -0,0 +1,36 @@
+(************************************************************************)
+(*  v      *   The Coq Proof Assistant  /  The Coq Development Team     *)
+(* <O___,, *   INRIA - CNRS - LIX - LRI - PPS - Copyright 1999-2016     *)
+(*   \VV/  **************************************************************)
+(*    //   *      This file is distributed under the terms of the       *)
+(*         *       GNU Lesser General Public License Version 2.1        *)
+(************************************************************************)
+
+(** This module defines the Ltac2 FFI to Ltac1 code. Due to intricate semantics
+    of the latter, the functions described here are voluntarily under-specified.
+    Not for the casual user, handle with care and expect undefined behaviours
+    otherwise. **)
+
+Require Import Ltac2.Init.
+
+Ltac2 Type t.
+(** Dynamically-typed Ltac1 values. *)
+
+Ltac2 @ external ref : ident list -> t := "ltac2" "ltac1_ref".
+(** Returns the Ltac1 definition with the given absolute name. *)
+
+Ltac2 @ external run : t -> unit := "ltac2" "ltac1_run".
+(** Runs an Ltac1 value, assuming it is a 'tactic', i.e. not returning
+    anything. *)
+
+Ltac2 @ external apply : t -> t list -> (t -> unit) -> unit := "ltac2" "ltac1_apply".
+(** Applies an Ltac1 value to a list of arguments, and provides the result in
+    CPS style. It does **not** run the returned value. *)
+
+(** Conversion functions *)
+
+Ltac2 @ external of_constr : constr -> t := "ltac2" "ltac1_of_constr".
+Ltac2 @ external to_constr : t -> constr option := "ltac2" "ltac1_to_constr".
+
+Ltac2 @ external of_list : t list -> t := "ltac2" "ltac1_of_list".
+Ltac2 @ external to_list : t -> t list option := "ltac2" "ltac1_to_list".