Merge pull request #1908 from shati-semmle/ql-hb/fixes

QL handbook: Add examples and fix typos

Author: jf205

docs/language/ql-handbook/predicates.rst

@@ -262,6 +262,10 @@ multiple binding set annotations, for example::
       x + 1 = y
     }
 
+    from int x, int y
+    where y = 42 and plusOne(x, y)
+    select x, y
+
 Multiple binding sets specified this way are independent of each other. The above example means:
   - If ``x`` is bound, then ``x`` and ``y`` are bound.
   - If ``y`` is bound, then ``x`` and ``y`` are bound.

docs/language/ql-handbook/queries.rst

@@ -83,7 +83,7 @@ For example::
       result = x * y
     }
 
-This predicates returns the following results: 
+This predicate returns the following results:
 
 +---+---+--------+
 | x | y | result |
@@ -96,8 +96,14 @@ This predicates returns the following results:
 +---+---+--------+
 
 A benefit of writing a query predicate instead of a select clause is that you can call the
-predicate in other parts of the code too. In contrast, the select clause is like an anonymous 
-predicate, so you can't call it later.
+predicate in other parts of the code too. For example, you can call ``getProduct`` inside
+the body of a :ref:`class <classes>`::
+
+    class MultipleOfThree extends int {
+      MultipleOfThree() { this = getProduct(_, _) }
+    }
+
+In contrast, the select clause is like an anonymous predicate, so you can't call it later.
 
 It can also be helpful to add a ``query`` annotation to a predicate while you debug code. That
 way you can explicitly see the set of tuples that the predicate evaluates to.

docs/language/ql-handbook/types.rst

@@ -106,7 +106,7 @@ base types.
 
 A class can extend multiple types. See :ref:`multiple-inheritance` below.
 
-To be a valid, a class:
+To be valid, a class:
   - Must not extend itself.
   - Must not extend a :ref:`final` class. 
   - Must not extend types that are incompatible. (See :ref:`type-compatibility`.)
@@ -147,7 +147,11 @@ predicate from the :ref:`above <defining-class>` class::
 
     1.(OneTwoThree).getAString()
 
-This call returns the results ``"One, two or three: 1"``.
+This call returns the result ``"One, two or three: 1"``.
+
+The expression ``(OneTwoThree)`` is a :ref:`cast <casts>`. It ensures that ``1`` has type
+``OneTwoThree`` instead of just ``int``. Therefore, it has access to the member predicate
+``getAString()``.
 
 Member predicates are especially useful because you can chain them together. For example, you
 can use ``toUpperCase()``, a built-in function defined for ``string``::