From: Siraaj Khandkar <siraaj@khandkar.net>
Date: Tue, 5 Jun 2018 16:55:03 +0000 (-0400)
Subject: Define the canonical map structure for Tiger
X-Git-Url: https://git.xandkar.net/?a=commitdiff_plain;h=2eadd9297a93ac7776a810ed44a547b67dddf32b;p=tiger.ml.git

Define the canonical map structure for Tiger

with a Red Black tree implementation, adapted from Okasaki.
---

diff --git a/compiler/src/lib/tiger/tiger_map.ml b/compiler/src/lib/tiger/tiger_map.ml
new file mode 100644
index 0000000..d31c9a8
--- /dev/null
+++ b/compiler/src/lib/tiger/tiger_map.ml
@@ -0,0 +1 @@
+include Tiger_map_red_black
diff --git a/compiler/src/lib/tiger/tiger_map_red_black.ml b/compiler/src/lib/tiger/tiger_map_red_black.ml
new file mode 100644
index 0000000..b339b52
--- /dev/null
+++ b/compiler/src/lib/tiger/tiger_map_red_black.ml
@@ -0,0 +1,101 @@
+module List = ListLabels
+
+type color = R | B
+type ('k, 'v) t =
+  | Leaf
+  | Node of color * ('k * 'v) * ('k, 'v) t * ('k, 'v) t
+
+let empty = Leaf
+
+let set t ~k ~v =
+  let balance = function
+             | Leaf -> assert false
+    (* LL *) | Node (B, x, Node (R, lx, Node (R, llx, lll, llr), lr                     ), r                                                              ) -> Node (R, lx , Node (B, llx, lll, llr), Node (B, x  , lr , r  ))
+    (* LR *) | Node (B, x, Node (R, lx, ll                     , Node (R, lrx, lrl, lrr)), r                                                              ) -> Node (R, lrx, Node (B, lx , ll , lrl), Node (B, x  , lrr, r  ))
+    (* RL *) | Node (B, x, l                                                             , Node (R, rx, Node (R, rlx, rll, rlr), rr                      )) -> Node (R, rlx, Node (B, x  , l  , rll), Node (B, rx , rlr, rr ))
+    (* RR *) | Node (B, x, l                                                             , Node (R, rx, rl                      , Node (R, rrx, rrl, rrr))) -> Node (R, rx , Node (B, x  , l  , rl ), Node (B, rrx, rrl, rrr))
+             | node -> node  (* Fragile pattern. Shall we reconsider? *)
+  in
+  let rec set t k v =
+    match t with
+    (* Because we recur, we cannot at this stage know if the following Node
+     * with Leaf children will end-up as root (in which case it should be
+     * black) or as the last node before leaves (in which case it should be
+     * red).  We begin by assuming that it is the later and at the very end,
+     * before returning to the caller, force the actual root node (which is
+     * easy to identify at that point) to be black, regardless of what it
+     * already is.
+     *)
+    | Leaf -> Node (R, (k, v), Leaf, Leaf)  (* Maybe root or last node, so R *)
+    | Node (c, ((k', _) as x), l, r) when k < k' -> balance (Node (c, x, set l k v, r))
+    | Node (c, ((k', _) as x), l, r) when k > k' -> balance (Node (c, x, l        , set r k v))
+    | Node (c, _             , l, r) -> Node (c, (k, v), l, r)
+  in
+  match set t k v with
+  | Leaf -> assert false  (* Can we GADT this away? *)
+  | Node (_, (k, v), l, r) -> Node (B, (k, v), l, r)  (* Root is always Black *)
+
+let rec get t ~k =
+  match t with
+  | Leaf -> None
+  | Node (_, (k', _), l, _) when k < k' -> get l ~k
+  | Node (_, (k', _), _, r) when k > k' -> get r ~k
+  | Node (_, (_ , v), _, _) -> Some v
+
+let rec member t ~k =
+  match t with
+  | Leaf -> false
+  | Node (_, (k', _), l, _) when k < k' -> member l ~k
+  | Node (_, (k', _), _, r) when k > k' -> member r ~k
+  | Node (_, (_ , _), _, _) -> true
+
+let to_edges t =
+  let rec to_edges_from node1 t =
+    match t with
+    | Leaf -> [(node1, `Leaf)]
+    | Node (c2, (k2, _), l, r) ->
+        let node2 = k2, c2 in
+        (node1, `Node node2) :: ((to_edges_from node2 l) @ (to_edges_from node2 r))
+  in
+  match t with
+  | Leaf ->
+      []
+  | Node (c, (k, _), l, r) ->
+      let node1 = k, c in
+      (to_edges_from node1 l) @ (to_edges_from node1 r)
+
+let color_to_string = function
+  | B -> "black"
+  | R -> "red"
+
+let to_dot t ~k_to_string =
+  let (dot_edges_and_nodes, _, _) =
+    List.fold_left
+      (to_edges t)
+      ~init:("", "\n", 0)
+      ~f:(fun (dot_edges_and_nodes, sep, leaves) ((k1, c1), node2_or_leaf) ->
+        let k1 = k_to_string k1 in
+        let k2, c2, leaves =
+          match node2_or_leaf with
+          | `Leaf ->
+              let leaves = succ leaves in
+              let label = Printf.sprintf "Leaf_%d" leaves in
+              (label, B, leaves)
+          | `Node (k2, c2) ->
+              let label = k_to_string k2 in
+              (label, c2, leaves)
+        in
+        let dot_edges_and_nodes =
+          Printf.sprintf
+            "%s%s    %S -> %S;\n    %S [color=%s,fontcolor=white,style=filled];\n    %S [color=%s,fontcolor=white,style=filled];\n"
+            dot_edges_and_nodes
+            sep
+            k1 k2
+            k1 (color_to_string c1)  (* Yes, it's redundant... *)
+            k2 (color_to_string c2)
+        in
+        let sep = "" in
+        (dot_edges_and_nodes, sep, leaves)
+    )
+  in
+  "digraph G {" ^ dot_edges_and_nodes ^ "}"
diff --git a/compiler/src/lib/tiger/tiger_map_red_black.mli b/compiler/src/lib/tiger/tiger_map_red_black.mli
new file mode 100644
index 0000000..3edafeb
--- /dev/null
+++ b/compiler/src/lib/tiger/tiger_map_red_black.mli
@@ -0,0 +1 @@
+include Tiger_map_sig.S
diff --git a/compiler/src/lib/tiger/tiger_map_sig.ml b/compiler/src/lib/tiger/tiger_map_sig.ml
new file mode 100644
index 0000000..521b6cf
--- /dev/null
+++ b/compiler/src/lib/tiger/tiger_map_sig.ml
@@ -0,0 +1,13 @@
+module type S = sig
+  type ('k, 'v) t
+
+  val empty : ('k, 'v) t
+
+  val set : ('k, 'v) t -> k:'k -> v:'v -> ('k, 'v) t
+
+  val get : ('k, 'v) t -> k:'k -> 'v option
+
+  val member : ('k, 'v) t -> k:'k -> bool
+
+  val to_dot : ('k, 'v) t -> k_to_string:('k -> string) -> string
+end