[MOREL-9] Allow '<expr>.<field>' as an alternative syntax for '#<fiel…

…d> <expr>'

README.md

@@ -125,6 +125,21 @@ Bugs:
 * Runtime should throw when divide by zero
 * Validator should give good user error when it cannot type an expression
 
+## Postfix labels
+
+As an extension to Standard ML, Morel allows '.' for field references.
+Thus `e.deptno` is equivalent to `#deptno e`.
+
+(Postfix labels are implemented as syntactic sugar; both expressions
+become an application of label `#deptno` to expression `e`.)
+
+Because '.' is left-associative, it is a more convenient syntax for
+chained references. In the standard syntax, `e.address.zipcode` would
+be written `#zipcode (#address e)`.
+
+The following relational examples use postfix labels, but the syntax
+is available in any Morel expression.
+
 ## Relational extensions
 
 The `from` expression (and associated `as`, `where` and `yield` keywords)
@@ -150,7 +165,7 @@ val depts =
 the expression
 
 ```
-from e in emps where (#deptno e = 30) yield (#id e)
+from e in emps where e.deptno = 30 yield e.id
 ```
 
 is equivalent to standard ML
@@ -176,8 +191,8 @@ a join or a cartesian product:
 
 ```
 from e in emps, d in depts
-  where (#deptno e) = (#deptno d)
-  yield {id = (#id e), deptno = (#deptno e), ename = (#name e), dname = (#name d)};
+  where e.deptno = d.deptno
+  yield {id = e.id, deptno = e.deptno, ename = e.name, dname = d.name};
 ```
 
 As in any ML expression, you can define functions within a `from` expression,
@@ -190,10 +205,10 @@ let
     | in_ e (h :: t) = e = h orelse (in_ e t)
 in
   from e in emps
-  where in_ (#deptno e) (from d in depts
-                where (#name d) = "Engineering"
-                yield (#deptno d))
-  yield (#name e)
+  where in_ e.deptno (from d in depts
+                where d.name = "Engineering"
+                yield d.deptno)
+  yield e.name
 end
 
 let
@@ -202,9 +217,9 @@ let
 in
   from e in emps
   where exists (from d in depts
-                where (#deptno d) = (#deptno e)
-                andalso (#name d) = "Engineering")
-  yield (#name e)
+                where d.deptno = e.deptno
+                andalso d.name = "Engineering")
+  yield e.name
 end
 ```
 

src/main/javacc/MorelParser.jj

@@ -418,8 +418,12 @@ Match match() :
 
 /** Parses an expression.
  *
- * <p>8 is the highest level of precedence. The full list is as follows:
+ * <p>8 is the highest level of precedence in standard ML,
+ and the '.field' extension is at level 9.
+ The full list is as follows:
+ *
  * <ul>
+ * <li>infix 9 {@code .}
  * <li>infix 8 (application)
  * <li>infix 7 {@code * / div mod}
  * <li>infix 6 {@code + - ^}
@@ -429,21 +433,39 @@ Match match() :
  * <li>infix 0 {@code before}
  * </ul>
  */
+Exp expression9() :
+{
+  Exp e;
+  Id id;
+}
+{
+  e = atom()
+  (
+    <DOT> id = identifier() {
+      final Exp s = ast.recordSelector(pos(), id.name);
+      e = ast.apply(s, e);
+    }
+  )*
+  { return e; }
+}
+
+/** Parses an expression of precedence level 8 (function application). */
 Exp expression8() :
 {
   Exp e;
   Exp e2;
 }
 {
-  e = atom()
+  e = expression9()
   (
-    e2 = atom() {
+    e2 = expression9() {
       e = ast.apply(e, e2);
     }
   )*
   { return e; }
 }
 
+/** Parses an expression of precedence level 7 (*, /, div, mod). */
 Exp expression7() :
 {
   Exp e;

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

@@ -24,6 +24,7 @@
 
 import net.hydromatic.morel.ast.Ast;
 import net.hydromatic.morel.ast.AstNode;
+import net.hydromatic.morel.parse.ParseException;
 import net.hydromatic.morel.type.TypeVar;
 
 import org.hamcrest.CustomTypeSafeMatcher;
@@ -46,6 +47,7 @@
 import static net.hydromatic.morel.Ml.assertError;
 import static net.hydromatic.morel.Ml.ml;
 
+import static org.hamcrest.CoreMatchers.containsString;
 import static org.hamcrest.CoreMatchers.is;
 import static org.hamcrest.CoreMatchers.not;
 import static org.hamcrest.CoreMatchers.nullValue;
@@ -272,6 +274,37 @@ public void describeTo(Description description) {
         + "3 *) 5 + 6").assertParse("5 + 6");
   }
 
+  /** Tests that the syntactic sugar "exp.field" is de-sugared to
+   * "#field exp". */
+  @Test public void testParseDot() {
+    ml("a . b")
+        .assertParse("#b a");
+    ml("a . b . c")
+        .assertParse("#c (#b a)");
+    ml("a . b + c . d")
+        .assertParse("#b a + #d c");
+    ml("a.b+c.d")
+        .assertParse("#b a + #d c");
+    ml("(a.b+c.d*e.f.g).h")
+        .assertParse("#h (#b a + #d c * #g (#f e))");
+    ml("a b")
+        .assertParse("a b");
+    ml("a b.c")
+        .assertParse("a (#c b)");
+    ml("a.b c.d e.f")
+        .assertParse("#b a (#d c) (#f e)");
+    ml("(a.b) (c.d) (e.f)")
+        .assertParse("#b a (#d c) (#f e)");
+    ml("(a.(b (c.d) (e.f))")
+        .assertParseThrows(
+            throwsA(ParseException.class,
+                containsString("Encountered \"(\" at line 1, column 4.")));
+    ml("(a.b c.(d (e.f)))")
+        .assertParseThrows(
+            throwsA(ParseException.class,
+                containsString("Encountered \"(\" at line 1, column 8.")));
+  }
+
   /** Tests the name of {@link TypeVar}. */
   @Test public void testTypeVarName() {
     assertError(() -> new TypeVar(-1).description(),
@@ -1239,6 +1272,22 @@ private <T extends Throwable> Matcher<Throwable> throwsA(Class<T> clazz,
                     list("ACCOUNTING", 7934))));
   }
 
+  /** As {@link #testScottJoin2()} but using dot notation ('e.field' rather
+   * than '#field e'). */
+  @Test public void testScottJoin2Dot() {
+    final String ml = "from e in scott.emp, d in scott.dept\n"
+        + "  where e.deptno = d.deptno\n"
+        + "  andalso e.empno >= 7900\n"
+        + "  yield {empno = e.empno, dname = d.dname}\n";
+    ml(ml)
+        .withBinding("scott", DataSet.SCOTT.foreignValue())
+        .assertType("{dname:string, empno:int} list")
+        .assertEval(
+            is(
+                list(list("SALES", 7900), list("RESEARCH", 7902),
+                    list("ACCOUNTING", 7934))));
+  }
+
   @Test public void testError() {
     ml("fn x y => x + y")
         .assertError(

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

@@ -139,6 +139,17 @@ Ml assertParseSame() {
     return assertParse(ml.replaceAll("[\n ]+", " "));
   }
 
+  Ml assertParseThrows(Matcher<Throwable> matcher) {
+    try {
+      final AstNode statement =
+          new MorelParserImpl(new StringReader(ml)).statement();
+      fail("expected error, got " + statement);
+    } catch (Throwable e) {
+      assertThat(e, matcher);
+    }
+    return this;
+  }
+
   private Ml withValidate(BiConsumer<Ast.Exp, TypeResolver.TypeMap> action) {
     return withParser(parser -> {
       try {

src/test/resources/script/relational.sml

@@ -49,28 +49,38 @@ from e in emps yield #id e;
 
 from e in emps yield (#id e) - 100;
 
+from e in emps yield e.id - 100;
+
 from e in emps yield #deptno e;
 
+from e in emps yield e.deptno;
+
 from e in emps yield {deptno = #deptno e, one = 1};
 
+from e in emps yield {deptno = e.deptno, one = 1};
+
 from e in emps yield ((#id e) + (#deptno e));
 
+from e in emps yield (e.id + e.deptno);
+
 from e2 in (from e in emps yield #deptno e) yield e2 + 1;
 
+from e2 in (from e in emps yield e.deptno) yield e2 + 1;
+
 (* Disabled: '=' should have lower precedence than '#deptno e' fun application
 from e in emps where #deptno e = 30 yield #name e;
 *)
 
-from e in emps where false yield (#deptno e);
+from e in emps where false yield e.deptno;
 
 (*) Function defined inside query
 from e in emps
-where #deptno e < 30
+where e.deptno < 30
 yield
   let
     fun p1 x = x + 1
   in
-    p1 (#id e)
+    p1 e.id
   end;
 
 (* Disabled due to CCE
@@ -90,18 +100,18 @@ from i in integers where i mod 2 = 1 yield i;
 (*) missing yield
 from i in integers where i mod 2 = 1;
 
-from e in emps where (#deptno e) = 30 yield (#id e);
+from e in emps where e.deptno = 30 yield e.id;
 
 (*) cartesian product
-from e in emps, e2 in emps yield (#name e) ^ "-" ^ (#name e2);
+from e in emps, e2 in emps yield e.name ^ "-" ^ e2.name;
 
 (*) cartesian product, missing yield
 from d in depts, i in integers;
 
 (*) join
 from e in emps, d in depts
-  where (#deptno e) = (#deptno d)
-  yield {id = (#id e), deptno = (#deptno e), ename = (#name e), dname = (#name d)};
+  where e.deptno = d.deptno
+  yield {id = e.id, deptno = e.deptno, ename = e.name, dname = d.name};
 
 (*) exists (defining the "exists" function ourselves)
 (*) and correlated sub-query
@@ -112,9 +122,9 @@ let
 in
   from e in emps
   where exists (from d in depts
-                where (#deptno d) = (#deptno e)
-                andalso (#name d) = "Engineering")
-  yield (#name e)
+                where d.deptno = e.deptno
+                andalso d.name = "Engineering")
+  yield e.name
 end;
 val it = ["Shaggy","Scooby"] : string list
 *)
@@ -126,10 +136,10 @@ let
     | in_ e (h :: t) = e = h orelse (in_ e t)
 in
   from e in emps
-  where in_ (#deptno e) (from d in depts
-                where (#name d) = "Engineering"
-                yield (#deptno d))
-  yield (#name e)
+  where in_ e.deptno (from d in depts
+                where d.name = "Engineering"
+                yield d.deptno)
+  yield e.name
 end;
 val it = ["Shaggy","Scooby"] : string list
 *)
@@ -161,8 +171,8 @@ end;
 
 (*) Basic 'group'
 from e in emps
-group (#deptno e) as deptno
-  compute sum of (#id e) as sumId,
+group e.deptno as deptno
+  compute sum of e.id as sumId,
           count of e as count;
 
 (*
@@ -173,29 +183,29 @@ val it =
 
 (*) 'group' with no aggregates
 from e in emps
-group (#deptno e) as deptno;
+group e.deptno as deptno;
 
 (*) composite 'group' with no aggregates
 from e in emps
-group (#deptno e) as deptno, (#id e) mod 2 as idMod2;
+group e.deptno as deptno, e.id mod 2 as idMod2;
 
 (*) 'group' with 'where' and complex argument to 'sum'
 (*
 from e in emps
-where (#deptno e) < 30
-group (#deptno e) as deptno
-  compute sum of (#id e) as sumId,
-          min of (#id e) + (#deptno e) as minIdPlusDeptno;
+where e.deptno < 30
+group e.deptno as deptno
+  compute sum of e.id as sumId,
+          min of e.id + e.deptno as minIdPlusDeptno;
 val it = [{deptno=10,id=100,name="Fred"},{deptno=20,id=101,name="Velma"}] : {deptno:int, id:int, name:string} list
 *)
 
 (*) 'group' with join
 (*
 from e in emps, d in depts
-where (#deptno e) = (#deptno d)
-group (#deptno e) as deptno,
- (#name e) as dname
-compute sum of (#id e) as sumId;
+where e.deptno = d.deptno
+group e.deptno as deptno,
+ e.name as dname
+compute sum of e.id as sumId;
 val it =
   [{d={deptno=10,name="Sales"},e={deptno=10,id=100,name="Fred"}},
    {d={deptno=20,name="HR"},e={deptno=20,id=101,name="Velma"}},
@@ -206,7 +216,7 @@ val it =
 (*) empty 'group'
 (*
 from e in emps
-group compute sum of (#id e) as sumId;
+group compute sum of e.id as sumId;
 val it =
   [{deptno=10,id=100,name="Fred"},{deptno=20,id=101,name="Velma"},
    {deptno=30,id=102,name="Shaggy"},{deptno=30,id=103,name="Scooby"}] : {deptno:int, id:int, name:string} list
@@ -217,7 +227,7 @@ val it =
 (*
 from emps as e
 group (#deptno e) as deptno
-  compute sum of (#id e) as sumId,
+  compute sum of e.id as sumId,
           count of e as count
   as g
 yield {deptno = (#deptno g), avgId = (#sumId g) / (#count g)}