Add a type of format strings to Ltac2.

It provides an abstract type of well-typed format strings, a scope to parse
them and a minimal printf-like API.

1 files changed, 56 insertions, 0 deletions

diff --git a/user-contrib/Ltac2/Printf.v b/user-contrib/Ltac2/Printf.v
new file mode 100644
index 0000000000..e2470ed1c3
--- /dev/null
+++ b/user-contrib/Ltac2/Printf.v
@@ -0,0 +1,56 @@
+(************************************************************************)
+(*         *   The Coq Proof Assistant / The Coq Development Team       *)
+(*  v      *         Copyright INRIA, CNRS and contributors             *)
+(* <O___,, * (see version control and CREDITS file for authors & dates) *)
+(*   \VV/  **************************************************************)
+(*    //   *    This file is distributed under the terms of the         *)
+(*         *     GNU Lesser General Public License Version 2.1          *)
+(*         *     (see LICENSE file for the text of the license)         *)
+(************************************************************************)
+
+Require Import Ltac2.Message.
+
+(** This file defines a printf notation for easiness of writing messages *)
+
+(**
+
+  The built-in "format" notation scope can be used to create well-typed variadic
+  printing commands following a printf-like syntax. The "format" scope parses
+  quoted strings which contain either raw string data or printing
+  specifications. Raw strings will be output verbatim as if they were passed
+  to Ltac2.Message.of_string.
+
+  Printing specifications are of the form
+
+  << '%' type >>
+
+  where the type value defines which kind of arguments will be accepted and
+  how they will be printed. They can take the following values.
+
+  - << i >>: takes an argument of type int and behaves as Message.of_int
+  - << I >>: takes an argument of type ident and behaves as Message.of_ident
+  - << s >>: takes an argument of type string and behaves as Message.of_string
+  - << t >>: takes an argument of type constr and behaves as Message.of_constr
+  - << a >>: takes two arguments << f >> of type << (unit -> 'a -> message) >>
+             and << x >> of type << 'a >> and behaves as << f () x >>
+  - << % >>: outputs << % >> verbatim
+
+  TODO: add printing modifiers.
+
+*)
+
+Ltac2 printf fmt := Format.kfprintf print fmt.
+Ltac2 fprintf fmt := Format.kfprintf (fun x => x) fmt.
+
+(** The two following notations are made available when this module is imported.
+
+    - printf will parse a format and generate a function taking the
+      corresponding arguments ant printing the resulting message as per
+      Message.print. In particular when fully applied it has type unit.
+    - fprintf behaves similarly but return the message as a value instead of
+      printing it.
+
+*)
+
+Ltac2 Notation "printf" fmt(format) := printf fmt.
+Ltac2 Notation "fprintf" fmt(format) := fprintf fmt.