[m-dev.] for review: two useful additions to map.m

[Ralph Becket]

I end up coding these functions so often I thought they should go
into map.m.

Ralph


estimated hours taken: 0.25

Added two functions to the map module that I often end up having to
code elsewhere.

library/map.m
        Added func map__add_to_list(Map, K, V).  V is consed onto the
        list value mapped to by K in Map (if such a mapping exists)
        or the mapping for K is set as [V] (otherwise).

        Added func map__add_to_set(Map, K, V) which is similar to the
        above, except that the value type for the mapping is set/1
        and the corresponding operations are set__insert/2 and
        set__make_singleton_list/1 respectively.

Index: map.m
===================================================================
RCS file: /home/mercury1/repository/mercury/library/map.m,v
retrieving revision 1.73
diff -u -u -r1.73 map.m
--- map.m       2000/03/31 01:05:47     1.73
+++ map.m       2000/05/29 13:11:54
@@ -106,6 +106,15 @@
 :- mode map__set(di, di, di, uo) is det.
 :- mode map__set(in, in, in, out) is det.

+    % Cons a new member onto the list value for the key or
+    % set the value for the key as the singleton list containing
+    % the new member if no mapping already exists.
+:- func map__add_to_list(map(K, list(V)), K, V) = map(K, list(V)).
+
+    % Similar to the above, except that the value type is a set
+    % rather than a list.
+:- func map__add_to_set(map(K, set(V)), K, V) = map(K, set(V)).
+
        % Given a map, return a list of all the keys in the map.
 :- pred map__keys(map(K, _V), list(K)).
 :- mode map__keys(in, out) is det.
@@ -767,4 +776,28 @@
 map__det_union(F, M1, M2) = M3 :-
        P = ( pred(X::in, Y::in, Z::out) is semidet :- Z = F(X, Y) ),
        map__det_union(P, M1, M2, M3).
+
+%
----------------------------------------------------------------------------
%
+
+map__add_to_list(Map, K, V) =
+    ( if
+        map__search(Map, K, Vs)
+      then
+        map__set(Map, K, [V | Vs])
+      else
+        map__set(Map, K, [V])
+    ).
+
+%
----------------------------------------------------------------------------
%
+
+map__add_to_set(Map, K, V) =
+    ( if
+        map__search(Map, K, Vs)
+      then
+        map__set(Map, K, set__insert(Vs, V))
+      else
+        map__set(Map, K, set__make_singleton_set(V))
+    ).
+


--
Ralph Becket      |      MSR Cambridge      |      rbeck at microsoft.com 
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