--- /dev/null
+(*
+ * Trie: maps over lists.
+ * Copyright (C) 2000 Jean-Christophe FILLIATRE
+ *
+ * This software is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License version 2, as published by the Free Software Foundation.
+ *
+ * This software is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ * See the GNU Library General Public License version 2 for more details
+ * (enclosed in the file LGPL).
+ *)
+
+(* $Id$ *)
+
+(*s A trie is a tree-like structure to implement dictionaries over
+ keys which have list-like structures. The idea is that each node
+ branches on an element of the list and stores the value associated
+ to the path from the root, if any. Therefore, a trie can be
+ defined as soon as a map over the elements of the list is
+ given. *)
+
+
+module Make (M : Map.S) = struct
+
+(*s Then a trie is just a tree-like structure, where a possible
+ information is stored at the node (['a option]) and where the sons
+ are given by a map from type [key] to sub-tries, so of type
+ ['a t M.t]. The empty trie is just the empty map. *)
+
+ type key = M.key list
+
+ type 'a t = Node of 'a option * 'a t M.t
+
+ let empty = Node (None, M.empty)
+
+(*s To find a mapping in a trie is easy: when all the elements of the
+ key have been read, we just inspect the optional info at the
+ current node; otherwise, we descend in the appropriate sub-trie
+ using [M.find]. *)
+
+ let rec find l t = match (l,t) with
+ | [], Node (None,_) -> raise Not_found
+ | [], Node (Some v,_) -> v
+ | x::r, Node (_,m) -> find r (M.find x m)
+
+ let rec mem l t = match (l,t) with
+ | [], Node (None,_) -> false
+ | [], Node (Some _,_) -> true
+ | x::r, Node (_,m) -> try mem r (M.find x m) with Not_found -> false
+
+(*s Insertion is more subtle. When the final node is reached, we just
+ put the information ([Some v]). Otherwise, we have to insert the
+ binding in the appropriate sub-trie [t']. But it may not exists,
+ and in that case [t'] is bound to an empty trie. Then we get a new
+ sub-trie [t''] by a recursive insertion and we modify the
+ branching, so that it now points to [t''], with [M.add]. *)
+
+ let add l v t =
+ let rec ins = function
+ | [], Node (_,m) -> Node (Some v,m)
+ | x::r, Node (v,m) ->
+ let t' = try M.find x m with Not_found -> empty in
+ let t'' = ins (r,t') in
+ Node (v, M.add x t'' m)
+ in
+ ins (l,t)
+
+(*s When removing a binding, we take care of not leaving bindings to empty
+ sub-tries in the nodes. Therefore, we test wether the result [t'] of
+ the recursive call is the empty trie [empty]: if so, we just remove
+ the branching with [M.remove]; otherwise, we modify it with [M.add]. *)
+
+ let rec remove l t = match (l,t) with
+ | [], Node (_,m) -> Node (None,m)
+ | x::r, Node (v,m) ->
+ try
+ let t' = remove r (M.find x m) in
+ Node (v, if t' = empty then M.remove x m else M.add x t' m)
+ with Not_found ->
+ t
+
+(*s The iterators [map], [mapi], [iter] and [fold] are implemented in
+ a straigthforward way using the corresponding iterators [M.map],
+ [M.mapi], [M.iter] and [M.fold]. For the last three of them,
+ we have to remember the path from the root, as an extra argument
+ [revp]. Since elements are pushed in reverse order in [revp],
+ we have to reverse it with [List.rev] when the actual binding
+ has to be passed to function [f]. *)
+
+ let rec map f = function
+ | Node (None,m) -> Node (None, M.map (map f) m)
+ | Node (Some v,m) -> Node (Some (f v), M.map (map f) m)
+
+ let mapi f t =
+ let rec maprec revp = function
+ | Node (None,m) ->
+ Node (None, M.mapi (fun x -> maprec (x::revp)) m)
+ | Node (Some v,m) ->
+ Node (Some (f (List.rev revp) v), M.mapi (fun x -> maprec (x::revp)) m)
+ in
+ maprec [] t
+
+ let iter f t =
+ let rec traverse revp = function
+ | Node (None,m) ->
+ M.iter (fun x -> traverse (x::revp)) m
+ | Node (Some v,m) ->
+ f (List.rev revp) v; M.iter (fun x t -> traverse (x::revp) t) m
+ in
+ traverse [] t
+
+ let rec fold f t acc =
+ let rec traverse revp t acc = match t with
+ | Node (None,m) ->
+ M.fold (fun x -> traverse (x::revp)) m acc
+ | Node (Some v,m) ->
+ f (List.rev revp) v (M.fold (fun x -> traverse (x::revp)) m acc)
+ in
+ traverse [] t acc
+
+ let compare cmp a b =
+ let rec comp a b = match a,b with
+ | Node (Some _, _), Node (None, _) -> 1
+ | Node (None, _), Node (Some _, _) -> -1
+ | Node (None, m1), Node (None, m2) ->
+ M.compare comp m1 m2
+ | Node (Some a, m1), Node (Some b, m2) ->
+ let c = cmp a b in
+ if c <> 0 then c else M.compare comp m1 m2
+ in
+ comp a b
+
+ let equal eq a b =
+ let rec comp a b = match a,b with
+ | Node (None, m1), Node (None, m2) ->
+ M.equal comp m1 m2
+ | Node (Some a, m1), Node (Some b, m2) ->
+ eq a b && M.equal comp m1 m2
+ | _ ->
+ false
+ in
+ comp a b
+
+ (* The base case is rather stupid, but constructable *)
+ let is_empty = function
+ | Node (None, m1) -> M.is_empty m1
+ | _ -> false
+
+end
projects / helm.git / blobdiff