Making detyping potentially lazy.

The internal detype function takes an additional arguments dictating
whether it should be eager or lazy.

We introduce a new type of delayed `DAst.t` AST nodes and use it for
`glob_constr`.

Such type, instead of only containing a value, it can contain a lazy
computation too. We use a GADT to discriminate between both uses
statically, so that no delayed terms ever happen to be
marshalled (which would raise anomalies).

We also fix a regression in the test-suite:

  Mixing laziness and effects is a well-known hell. Here, an exception
  that was raised for mere control purpose was delayed and raised at a
  later time as an anomaly. We make the offending function eager.

1 files changed, 41 insertions, 0 deletions

diff --git a/lib/dAst.ml b/lib/dAst.ml
new file mode 100644
index 000000000..0fe323d01
--- /dev/null
+++ b/lib/dAst.ml
@@ -0,0 +1,41 @@
+(************************************************************************)
+(*  v      *   The Coq Proof Assistant  /  The Coq Development Team     *)
+(* <O___,, *   INRIA - CNRS - LIX - LRI - PPS - Copyright 1999-2017     *)
+(*   \VV/  **************************************************************)
+(*    //   *      This file is distributed under the terms of the       *)
+(*         *       GNU Lesser General Public License Version 2.1        *)
+(************************************************************************)
+
+open CAst
+
+type ('a, _) thunk =
+| Value : 'a -> ('a, 'b) thunk
+| Thunk : 'a Lazy.t -> ('a, [ `thunk ]) thunk
+
+type ('a, 'b) t = ('a, 'b) thunk CAst.t
+
+let map_thunk (type s) f : (_, s) thunk -> (_, s) thunk = function
+| Value x -> Value (f x)
+| Thunk k -> Thunk (lazy (f (Lazy.force k)))
+
+let get_thunk (type s) : ('a, s) thunk -> 'a = function
+| Value x -> x
+| Thunk k -> Lazy.force k
+
+let get x = get_thunk x.v
+
+let make ?loc v = CAst.make ?loc (Value v)
+
+let delay ?loc v = CAst.make ?loc (Thunk (Lazy.from_fun v))
+
+let map f n = CAst.map (fun x -> map_thunk f x) n
+
+let map_with_loc f n =
+  CAst.map_with_loc (fun ?loc x -> map_thunk (fun x -> f ?loc x) x) n
+
+let map_from_loc f (loc, x) =
+  make ?loc (f ?loc x)
+
+let with_val f n = f (get n)
+
+let with_loc_val f n = f ?loc:n.CAst.loc (get n)