From 25b0fb0c624766826758ec7ab526b4be5e85dcf2 Mon Sep 17 00:00:00 2001
From: Boris Okner <boris.okner@gmail.com>
Date: Mon, 16 Dec 2024 10:09:52 -0500
Subject: [PATCH] Minor changes to propagator code; 'reduce' fun for subsets of
 damain values

---
 lib/solver/core/constraint.ex            | 22 +++++++++++++------
 lib/solver/core/propagator/propagator.ex |  6 +++++-
 lib/solver/domain/bitvector_domain.ex    | 27 ++++++++++++------------
 lib/solver/model/model.ex                |  9 +++++++-
 4 files changed, 43 insertions(+), 21 deletions(-)

diff --git a/lib/solver/core/constraint.ex b/lib/solver/core/constraint.ex
index 8888861..6c7710c 100644
--- a/lib/solver/core/constraint.ex
+++ b/lib/solver/core/constraint.ex
@@ -29,18 +29,28 @@ defmodule CPSolver.Constraint do
       {constraint_impl, args}
   end
 
-  def constraint_to_propagators({constraint_mod, args}) when is_list(args) do
-    constraint_mod.propagators(args)
+  def constraint_to_propagators(constraint, reducer_fun \\ &Function.identity/1)
+
+  def constraint_to_propagators({constraint_mod, args}, reducer_fun) when is_list(args) do
+    List.foldr(constraint_mod.propagators(args), [], fn p, plist_acc ->
+      [reducer_fun.(p) | plist_acc]
+    end)
   end
 
-  def constraint_to_propagators(constraint) when is_tuple(constraint) do
+  def constraint_to_propagators(constraint, reducer_fun) when is_tuple(constraint) do
     [constraint_mod | args] = Tuple.to_list(constraint)
-    constraint_to_propagators({constraint_mod, args})
+    constraint_to_propagators({constraint_mod, args}, reducer_fun)
   end
 
   def post(constraint) when is_tuple(constraint) do
-    propagators = constraint_to_propagators(constraint)
-    Enum.map(propagators, fn p -> Propagator.filter(p) end)
+    constraint_to_propagators(constraint,
+    fn p ->
+      case Propagator.filter(p) do
+           :fail -> throw({:fail, p.id})
+           %{state: state} -> Propagator.update_state(p, state)
+           _ -> p
+      end
+    end)
   end
 
   def extract_variables(constraint) do
diff --git a/lib/solver/core/propagator/propagator.ex b/lib/solver/core/propagator/propagator.ex
index 2c8b6c8..2d0676d 100644
--- a/lib/solver/core/propagator/propagator.ex
+++ b/lib/solver/core/propagator/propagator.ex
@@ -108,7 +108,11 @@ defmodule CPSolver.Propagator do
   end
 
   def reset(%{mod: mod, args: args} = propagator, opts \\ []) do
-    Map.put(propagator, :state, mod.reset(args, Map.get(propagator, :state), opts))
+    update_state(propagator, mod.reset(args, Map.get(propagator, :state), opts))
+  end
+
+  def update_state(propagator, state) do
+    Map.put(propagator, :state, state)
   end
 
   def bind(%{mod: mod} = propagator, source, var_field \\ :domain) do
diff --git a/lib/solver/domain/bitvector_domain.ex b/lib/solver/domain/bitvector_domain.ex
index 8b4a116..94b87ec 100644
--- a/lib/solver/domain/bitvector_domain.ex
+++ b/lib/solver/domain/bitvector_domain.ex
@@ -59,38 +59,39 @@ defmodule CPSolver.BitVectorDomain do
     to_list(domain, mapper_fun)
   end
 
-  def to_list(
-        {{:bit_vector, ref} = bit_vector, offset} = domain,
-        mapper_fun \\ &Function.identity/1
-      ) do
+  ## Reduce over domain values
+  def reduce( {{:bit_vector, ref} = bit_vector, offset} = domain, value_mapper_fun, reduce_fun \\ &MapSet.union/2, acc_init \\ MapSet.new()) do
     %{
       min_addr: %{block: current_min_block, offset: _min_offset},
       max_addr: %{block: current_max_block, offset: _max_offset}
     } = get_bound_addrs(bit_vector)
 
-    mapped_lb = mapper_fun.(min(domain))
-    mapped_ub = mapper_fun.(max(domain))
+    mapped_lb = value_mapper_fun.(min(domain))
+    mapped_ub = value_mapper_fun.(max(domain))
 
-    ## Note: this will only work for monotonic mapper functions.
-    ## We don't have non-monotonic mappers for the moment.
-    ##
-    ## Adjust bounds
     {lb, ub} = (mapped_lb <= mapped_ub && {mapped_lb, mapped_ub}) || {mapped_ub, mapped_lb}
 
-    Enum.reduce(current_min_block..current_max_block, MapSet.new(), fn idx, acc ->
+    Enum.reduce(current_min_block..current_max_block, acc_init, fn idx, acc ->
       n = :atomics.get(ref, idx)
 
       if n == 0 do
         acc
       else
-        MapSet.union(
+        reduce_fun.(
           acc,
-          bit_positions(n, fn val -> {lb, ub, mapper_fun.(val + 64 * (idx - 1) - offset)} end)
+          bit_positions(n, fn val -> {lb, ub, value_mapper_fun.(val + 64 * (idx - 1) - offset)} end)
         )
       end
     end)
   end
 
+  def to_list(
+        {{:bit_vector, ref} = bit_vector, offset} = domain,
+        value_mapper_fun \\ &Function.identity/1
+      ) do
+        reduce(domain, value_mapper_fun, &MapSet.union/2, MapSet.new())
+  end
+
   def fixed?({bit_vector, _offset} = _domain) do
     {current_min_max, _min_max_idx, current_min, current_max} = get_min_max(bit_vector)
     current_max == current_min && current_min_max != @failure_value
diff --git a/lib/solver/model/model.ex b/lib/solver/model/model.ex
index 3931b04..4c9175f 100644
--- a/lib/solver/model/model.ex
+++ b/lib/solver/model/model.ex
@@ -16,7 +16,14 @@ defmodule CPSolver.Model do
         }
 
   def new(variables, constraints, opts \\ []) do
-    constraints = normalize_constraints(constraints)
+    constraints =
+    normalize_constraints(constraints)
+    # TODO:
+    # consider posting constraints and/or building constraint graph/list of propagators here
+    ## For instance:
+    # tap(fn constraints -> Enum.each(constraints, fn c -> Constraint.post(c) end) end)
+    #
+
     {all_variables, objective} = init_model(variables, constraints, opts[:objective])
 
     %__MODULE__{