Upgrade sorting function

docs/sophia_stdlib.md

@@ -975,12 +975,20 @@ List.unzip(l : list('a * 'b)) : list('a) * list('b)
 Opposite to the `zip` operation. Takes a list of pairs and returns pair of lists with respective elements on same indices.
 
 
+### merge
+```
+List.merge(lesser_cmp : ('a, 'a) => bool, l1 : list('a), l2 : list('a)) : list('a)
+```
+
+Merges two sorted lists into a single sorted list. O(length(l1) + length(l2))
+
+
 ### sort
 ```
 List.sort(lesser_cmp : ('a, 'a) => bool, l : list('a)) : list('a)
 ```
 
-Sorts a list using given comparator. `lesser_cmp(x, y)` should return `true` iff `x < y`. If `lesser_cmp` is not transitive or there exists an element `x` such that `lesser_cmp(x, x)` or there exists a pair of elements `x` and `y` such that `lesser_cmp(x, y) && lesser_cmp(y, x)` then the result is undefined. Currently O(n^2).
+Sorts a list using given comparator. `lesser_cmp(x, y)` should return `true` iff `x < y`. If `lesser_cmp` is not transitive or there exists an element `x` such that `lesser_cmp(x, x)` or there exists a pair of elements `x` and `y` such that `lesser_cmp(x, y) && lesser_cmp(y, x)` then the result is undefined. O(length(l) * log_2(length(l))).
 
 
 ### intersperse

priv/stdlib/List.aes

@@ -227,11 +227,67 @@ namespace List =
     (left, right)::t => unzip_(t, left::acc_l, right::acc_r)
 
 
-  // TODO: Improve?
-  function sort(lesser_cmp : ('a, 'a) => bool, l : list('a)) : list('a) = switch(l)
-    []   => []
-    h::t => switch (partition((x) => lesser_cmp(x, h), t))
-      (lesser, bigger) => sort(lesser_cmp, lesser) ++ h::sort(lesser_cmp, bigger)
+  /** Merges two sorted lists using `lt` comparator
+   */
+  function
+    merge : (('a, 'a) => bool, list('a), list('a)) => list('a)
+    merge(lt, x::xs, y::ys) =
+      if(lt(x, y)) x::merge(lt, xs, y::ys)
+      else y::merge(lt, x::xs, ys)
+    merge(_, [], ys) = ys
+    merge(_, xs, []) = xs
+
+
+  /** Mergesort inspired by
+   * https://hackage.haskell.org/package/base-4.14.1.0/docs/src/Data.OldList.html#sort
+   */
+  function
+    sort : (('a, 'a) => bool, list('a)) => list('a)
+    sort(_, []) = []
+    sort(lt, l) =
+      merge_all(lt, monotonic_subs(lt, l))
+
+  /** Splits list into compound increasing sublists
+   */
+  private function
+    monotonic_subs : (('a, 'a) => bool, list('a)) => list(list('a))
+    monotonic_subs(lt, x::y::rest) =
+      if(lt(y, x)) desc(lt, y, [x], rest)
+      else asc(lt, y, [x], rest)
+    monotonic_subs(_, l) = [l]
+
+  /** Extracts the longest descending prefix and proceeds with monotonic split
+   */
+  private function
+    desc : (('a, 'a) => bool, 'a, list('a), list('a)) => list(list('a))
+    desc(lt, x, acc, h::t) =
+      if(lt(x, h)) (x::acc) :: monotonic_subs(lt, h::t)
+      else desc(lt, h, x::acc, t)
+    desc(_, x, acc, []) = [x::acc]
+
+  /** Extracts the longest ascending prefix and proceeds with monotonic split
+   */
+  private function
+    asc : (('a, 'a) => bool, 'a, list('a), list('a)) => list(list('a))
+    asc(lt, x, acc, h::t) =
+      if(lt(h, x)) List.reverse(x::acc) :: monotonic_subs(lt, h::t)
+      else asc(lt, h, x::acc, t)
+    asc(_, x, acc, []) = [List.reverse(x::acc)]
+
+  /** Merges list of sorted lists
+   */
+  private function
+    merge_all : (('a, 'a) => bool, list(list('a))) => list('a)
+    merge_all(_, [part]) = part
+    merge_all(lt, parts) = merge_all(lt, merge_pairs(lt, parts))
+
+  /** Single round of `merge_all` – pairs of lists in a list of list
+   */
+  private function
+    merge_pairs : (('a, 'a) => bool, list(list('a))) => list(list('a))
+    merge_pairs(lt, x::y::rest) = merge(lt, x, y) :: merge_pairs(lt, rest)
+    merge_pairs(_, l) = l
+
 
 /** Puts `delim` between every two members of the list
  */

src/aeso_ast_infer_types.erl

@@ -1557,15 +1557,6 @@ free_vars(L) when is_list(L) ->
     [V || Elem <- L,
           V <- free_vars(Elem)].
 
-next_count() ->
-    V = case get(counter) of
-            undefined ->
-                0;
-            X -> X
-        end,
-    put(counter, V + 1),
-    V.
-
 %% Clean up all the ets tables (in case of an exception)
 
 ets_tables() ->
@@ -1611,18 +1602,6 @@ ets_tab2list(Name) ->
     TabId = ets_tabid(Name),
     ets:tab2list(TabId).
 
-ets_insert_ordered(_, []) -> true;
-ets_insert_ordered(Name, [H|T]) ->
-    ets_insert_ordered(Name, H),
-    ets_insert_ordered(Name, T);
-ets_insert_ordered(Name, Object) ->
-    Count = next_count(),
-    TabId = ets_tabid(Name),
-    ets:insert(TabId, {Count, Object}).
-
-ets_tab2list_ordered(Name) ->
-    [E || {_, E} <- ets_tab2list(Name)].
-
 %% Options
 
 create_options(Options) ->
@@ -1658,17 +1637,17 @@ destroy_and_report_unsolved_constraints(Env) ->
 %% -- Named argument constraints --
 
 create_named_argument_constraints() ->
-    ets_new(named_argument_constraints, [ordered_set]).
+    ets_new(named_argument_constraints, [bag]).
 
 destroy_named_argument_constraints() ->
     ets_delete(named_argument_constraints).
 
 get_named_argument_constraints() ->
-    ets_tab2list_ordered(named_argument_constraints).
+    ets_tab2list(named_argument_constraints).
 
 -spec add_named_argument_constraint(named_argument_constraint()) -> ok.
 add_named_argument_constraint(Constraint) ->
-    ets_insert_ordered(named_argument_constraints, Constraint),
+    ets_insert(named_argument_constraints, Constraint),
     ok.
 
 solve_named_argument_constraints(Env) ->
@@ -1707,14 +1686,14 @@ destroy_and_report_unsolved_named_argument_constraints(Env) ->
                          | {add_bytes, aeso_syntax:ann(), concat | split, utype(), utype(), utype()}.
 
 create_bytes_constraints() ->
-    ets_new(bytes_constraints, [ordered_set]).
+    ets_new(bytes_constraints, [bag]).
 
 get_bytes_constraints() ->
-    ets_tab2list_ordered(bytes_constraints).
+    ets_tab2list(bytes_constraints).
 
 -spec add_bytes_constraint(byte_constraint()) -> true.
 add_bytes_constraint(Constraint) ->
-    ets_insert_ordered(bytes_constraints, Constraint).
+    ets_insert(bytes_constraints, Constraint).
 
 solve_bytes_constraints(Env) ->
     [ solve_bytes_constraint(Env, C) || C <- get_bytes_constraints() ],
@@ -1768,18 +1747,18 @@ check_bytes_constraint(Env, {add_bytes, Ann, Fun, A0, B0, C0}) ->
 
 create_field_constraints() ->
     %% A relation from uvars to constraints
-    ets_new(field_constraints, [ordered_set]).
+    ets_new(field_constraints, [bag]).
 
 destroy_field_constraints() ->
     ets_delete(field_constraints).
 
 -spec constrain([field_constraint()]) -> true.
 constrain(FieldConstraints) ->
-    ets_insert_ordered(field_constraints, FieldConstraints).
+    ets_insert(field_constraints, FieldConstraints).
 
 -spec get_field_constraints() -> [field_constraint()].
 get_field_constraints() ->
-    ets_tab2list_ordered(field_constraints).
+    ets_tab2list(field_constraints).
 
 solve_field_constraints(Env) ->
     FieldCs =