[clib] Provide `filter_range` function.

This is very useful to compute efficiently a list of prefixes. Will be
used in conjunction with the nametab to provide completion.

Example of use:

```
let cprefix x y = String.(compare x (sub y 0 (min (length x) (length y)))) in
M.filter_range (cprefix "foo") m
```

We could of course maintain a trie, but this is less invasive an
should work at our scale.

1 files changed, 6 insertions, 0 deletions

diff --git a/clib/cMap.mli b/clib/cMap.mli
index f5496239f6..ca6ddb2f4e 100644
--- a/clib/cMap.mli
+++ b/clib/cMap.mli
@@ -60,6 +60,12 @@ sig
   val height : 'a t -> int
   (** An indication of the logarithmic size of a map *)
 
+  val filter_range : (key -> int) -> 'a t -> 'a t
+  (** [find_range in_range m] Given a comparison function [in_range x],
+      that tests if [x] is below, above, or inside a given range
+      [filter_range] returns the submap of [m] whose keys are in
+      range. Note that [in_range] has to define a continouous range. *)
+
   module Smart :
   sig
     val map : ('a -> 'a) -> 'a t -> 'a t