user-defined aggregate function

src/main/java/net/hydromatic/morel/compile/TypeResolver.java

@@ -651,7 +651,7 @@ private Triple deduceStepType(TypeEnv env, Ast.FromStep step, Triple triple,
         reg(aggregate.aggregate, null, v9);
         equiv(
             unifier.apply(FN_TY_CON,
-                unifier.apply(STREAM_TY_CON, unifier.variable(), v10), v8),
+                unifier.apply(STREAM_TY_CON, unorderedTerm(), v10), v8),
             v9);
         env3 = env3.bind(id.name, v8);
         fieldVars.put(id, v8);

src/test/java/net/hydromatic/morel/MainTest.java

@@ -2479,7 +2479,10 @@ private static List<Object> node(Object... args) {
         + "    [{id = 100, name = \"Fred\", deptno = 10},\n"
         + "     {id = 101, name = \"Velma\", deptno = 20},\n"
         + "     {id = 102, name = \"Shaggy\", deptno = 10}]\n"
-        + "  fun sum [] = 0 | sum (h::t) = h + (sum t)\n"
+        + "  fun sum bag =\n"
+        + "    case Bag.getItem bag of\n"
+        + "        NONE => 0\n"
+        + "      | SOME (h, t) => h + (sum t)\n"
         + "in\n"
         + "  from e in emps\n"
         + "    group #deptno e\n"
@@ -2489,7 +2492,9 @@ private static List<Object> node(Object... args) {
         + "[{deptno = 10, id = 100, name = \"Fred\"},"
         + " {deptno = 20, id = 101, name = \"Velma\"},"
         + " {deptno = 10, id = 102, name = \"Shaggy\"}]; "
-        + "fun sum ([]) = 0 | sum (h :: t) = h + sum t "
+        + "fun sum bag = case #getItem Bag bag of"
+        + " NONE => 0"
+        + " | SOME (h, t) => h + sum t "
         + "in"
         + " from e in emps"
         + " group deptno = #deptno e"
@@ -2551,7 +2556,7 @@ private static List<Object> node(Object... args) {
 
     ml("from e in [{a = 1, b = 5}, {a = 0, b = 1}, {a = 1, b = 1}]\n"
         + "  group e.a compute rows = (fn x => x)")
-        .assertType(hasMoniker("{a:int, rows:{a:int, b:int} list} bag"))
+        .assertType(hasMoniker("{a:int, rows:{a:int, b:int} bag} bag"))
         .assertEvalIter(
             equalsUnordered(
                 list(1, list(list(1, 5), list(1, 1))),

src/test/resources/script/bag.smli

@@ -102,7 +102,9 @@ from r in recList group r.i;
 from r in recBag group r.i;
 > val it = [1,2] : int bag
 
-(*) aggregate functions produce bags
+(*) the input to an aggregate functions is a bag, even if the input
+(*) stream is a list. (We need to devise syntax for aggregate functions
+(*) to sort their input.)
 from r in recList group r.i compute count;
 > val it = [{count=2,i=1},{count=1,i=2}] : {count:int, i:int} bag
 from r in recBag group r.i compute count;
@@ -128,9 +130,9 @@ from i in intList order ();
 from i in intBag order ();
 > val it = [1,2,3] : int list
 from r in recList group r.i compute bs = (fn x => x) of r.b order i desc;
-> val it = [{bs=[true,false],i=1},{bs=[false],i=2}] : {bs:bool bag, i:int} list
+> val it = [{bs=[false],i=2},{bs=[true,false],i=1}] : {bs:bool bag, i:int} list
 from r in recBag group r.i compute bs = (fn x => x) of r.b order i desc;
-> val it = [{bs=[true,false],i=1},{bs=[false],i=2}] : {bs:bool bag, i:int} list
+> val it = [{bs=[false],i=2},{bs=[true,false],i=1}] : {bs:bool bag, i:int} list
 
 (*) join preserves collection type (should it?)