[m-rev.] for review: Add hash table lookup predicates.

[Peter Wang]

library/hash_table.m:
    Add lookup predicate.

library/version_hash_table.m:
    Add lookup predicate.

    Use higher-order field type with insts; delete inst casts.

    Use predicates instead of functions in a couple of places.

NEWS:
    Announce additions.
---
 NEWS                         |  8 +++++
 library/hash_table.m         | 14 +++++---
 library/version_hash_table.m | 70 +++++++++++++-----------------------
 3 files changed, 43 insertions(+), 49 deletions(-)

diff --git a/NEWS b/NEWS
index 36950e063..e303cbddb 100644
--- a/NEWS
+++ b/NEWS
@@ -110,6 +110,10 @@ Changes to the Mercury standard library
 
 ### Changes to the `hash_table` module
 
+* The following predicate has been added:
+
+    - pred `lookup/3`
+
 * The following obsolete predicates have been removed:
 
     - pred `char_hash/2`
@@ -693,6 +697,10 @@ Changes to the Mercury standard library
 
 ### Changes to the `version_hash_table` module
 
+* The following predicate has been added:
+
+    - pred `lookup/3`
+
 * The following obsolete predicates have been removed:
 
     - pred `char_hash/2`
diff --git a/library/hash_table.m b/library/hash_table.m
index 359e5451c..c91ff14bf 100644
--- a/library/hash_table.m
+++ b/library/hash_table.m
@@ -168,6 +168,9 @@
 :- mode lookup(hash_table_ui, in) = out is det.
 % :- mode lookup(in, in) = out is det.
 
+:- pred lookup(hash_table(K, V), K, V).
+:- mode lookup(hash_table_ui, in, out) is det.
+
     % Field access for hash tables.
     % HT ^ elem(K) is equivalent to lookup(HT, K).
     %
@@ -590,11 +593,14 @@ hash_bucket_search(HB, Key, Value) :-
 
 %---------------------------------------------------------------------------%
 
-lookup(HT, K) =
-    ( if V = search(HT, K) then
-        V
+lookup(HT, K) = V :-
+    lookup(HT, K, V).
+
+lookup(HT, K, V) :-
+    ( if search(HT, K, V0) then
+        V = V0
     else
-        func_error($pred, "key not found")
+        error($pred, "key not found")
     ).
 
 % XXX The convention in other library modules is that
diff --git a/library/version_hash_table.m b/library/version_hash_table.m
index 5a2fa60b1..d4c7a823c 100644
--- a/library/version_hash_table.m
+++ b/library/version_hash_table.m
@@ -108,6 +108,7 @@
     % if there is no entry for the key.
     %
 :- func lookup(version_hash_table(K, V), K) = V.
+:- pred lookup(version_hash_table(K, V)::in, K::in, V::out) is det.
 
     % Field access for hash tables.
     % `HT ^ elem(K)' is equivalent to `lookup(HT, K)'.
@@ -157,8 +158,7 @@
     % are the same as for init/3 above.
     %
 :- func from_assoc_list(hash_pred(K)::in(hash_pred), int::in, float::in,
-        assoc_list(K, V)::in) =
-    (version_hash_table(K, V)::out) is det.
+    assoc_list(K, V)::in) = (version_hash_table(K, V)::out) is det.
 
     % A simpler version of from_assoc_list/4, the values for N and
     % MaxOccupancy are configured with defaults such as in init_default/1
@@ -212,7 +212,7 @@
     --->    ht(
                 ht_num_occupants        :: int,
                 ht_max_occupants        :: int,
-                ht_hash_pred            :: hash_pred(K),
+                ht_hash_pred            :: pred(K::in, int::out) is det,
                 ht_buckets              :: buckets(K, V)
             )
     where equality is version_hash_table.equal.
@@ -230,14 +230,16 @@
 
 %---------------------------------------------------------------------------%
 
-init(HashPred, N, MaxOccupancy) = init_2(HashPred, N, MaxOccupancy, yes).
+init(HashPred, N, MaxOccupancy) = HT :-
+    do_init(HashPred, N, MaxOccupancy, yes, HT).
 
-unsafe_init(HashPred, N, MaxOccupancy) = init_2(HashPred, N, MaxOccupancy, no).
+unsafe_init(HashPred, N, MaxOccupancy) = HT :-
+    do_init(HashPred, N, MaxOccupancy, no, HT).
 
-:- func init_2(hash_pred(K)::in(hash_pred), int::in, float::in, bool::in) =
-    (version_hash_table(K, V)::out) is det.
+:- pred do_init(hash_pred(K)::in(hash_pred), int::in, float::in, bool::in,
+    version_hash_table(K, V)::out) is det.
 
-init_2(HashPred, N, MaxOccupancy, NeedSafety) = HT :-
+do_init(HashPred, N, MaxOccupancy, NeedSafety, HT) :-
     ( if N =< 0 then
         error("version_hash_table.init: N =< 0")
     else if N >= int.bits_per_int then
@@ -289,10 +291,9 @@ num_occupants(HT) = NumOccupants :-
 :- pragma inline(func(find_slot/2)).
 
 find_slot(HT, K) = H :-
-    promise_equivalent_solutions [HashPred0] (
-        HashPred0 = HT ^ ht_hash_pred
+    promise_equivalent_solutions [HashPred] (
+        HashPred = HT ^ ht_hash_pred
     ),
-    unsafe_hash_pred_cast(HashPred0, HashPred),
     find_slot_2(HashPred, K, HT ^ num_buckets, H).
 
 :- pred find_slot_2(hash_pred(K)::in(hash_pred), K::in, int::in, int::out)
@@ -304,30 +305,6 @@ find_slot_2(HashPred, K, NumBuckets, H) :-
     % Since NumBuckets is a power of two we can avoid mod.
     H = Hash /\ (NumBuckets - 1).
 
-:- pred unsafe_hash_pred_cast(hash_pred(K)::in, hash_pred(K)::out(hash_pred))
-    is det.
-
-:- pragma foreign_proc("C",
-    unsafe_hash_pred_cast(HashPred0::in, HashPred::out(hash_pred)),
-    [will_not_call_mercury, promise_pure, thread_safe],
-"
-    HashPred = HashPred0;
-").
-
-:- pragma foreign_proc("C#",
-    unsafe_hash_pred_cast(HashPred0::in, HashPred::out(hash_pred)),
-    [will_not_call_mercury, promise_pure, thread_safe],
-"
-    HashPred = HashPred0;
-").
-
-:- pragma foreign_proc("Java",
-    unsafe_hash_pred_cast(HashPred0::in, HashPred::out(hash_pred)),
-    [will_not_call_mercury, promise_pure, thread_safe],
-"
-    HashPred = HashPred0;
-").
-
 %---------------------------------------------------------------------------%
 
 copy(HT0) = HT :-
@@ -340,6 +317,9 @@ copy(HT0) = HT :-
 %---------------------------------------------------------------------------%
 
 search(HT, K) = V :-
+    search(HT, K, V).
+
+search(HT, K, V) :-
     H = find_slot(HT, K),
     promise_equivalent_solutions [Buckets] (
         Buckets = HT ^ ht_buckets
@@ -347,8 +327,6 @@ search(HT, K) = V :-
     AL = Buckets ^ elem(H),
     alist_search(AL, K, V).
 
-search(HT, K, search(HT, K)).
-
 :- pred alist_search(hash_table_alist(K, V)::in, K::in, V::out) is semidet.
 
 alist_search(AL, K, V) :-
@@ -369,11 +347,14 @@ alist_search(AL, K, V) :-
 
 %---------------------------------------------------------------------------%
 
-lookup(HT, K) =
-    ( if V = search(HT, K) then
-        V
+lookup(HT, K) = V :-
+    lookup(HT, K, V).
+
+lookup(HT, K, V) :-
+    ( if search(HT, K, V0) then
+        V = V0
     else
-        func_error($pred, "key not found")
+        error($pred, "key not found")
     ).
 
 elem(K, HT) = lookup(HT, K).
@@ -595,15 +576,14 @@ from_assoc_list_2([K - V | T], !HT) :-
     % argument is not eliminated, nor is the creation of the type_info
     % delayed until the (rare) call to expand.
     %
-:- func expand(int, int, hash_pred(K), buckets(K, V)) =
-    version_hash_table(K, V).
+:- func expand(int::in, int::in, hash_pred(K)::in(hash_pred),
+    buckets(K, V)::in) = (version_hash_table(K, V)::out) is det.
 :- pragma no_inline(func(expand/4)).
 
-expand(NumOccupants, MaxOccupants0, HashPred0, Buckets0) = HT :-
+expand(NumOccupants, MaxOccupants0, HashPred, Buckets0) = HT :-
     NumBuckets0 = size(Buckets0),
     NumBuckets = NumBuckets0 + NumBuckets0,
     MaxOccupants = MaxOccupants0 + MaxOccupants0,
-    unsafe_hash_pred_cast(HashPred0, HashPred),
     Buckets1 = version_array.init(NumBuckets, ht_nil),
     reinsert_bindings(0, Buckets0, HashPred, NumBuckets, Buckets1, Buckets),
     HT = ht(NumOccupants, MaxOccupants, HashPred, Buckets).
-- 
2.38.0