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Diffstat (limited to 'demo/prose')
| -rw-r--r-- | demo/prose | 4 |
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@@ -139,6 +139,10 @@ outer.urp <p>SQL outer joins are no problem, as this demo shows. Unlike with SQL, here we have static type inference determining for us which columns may become nullable as a result of an outer join, and the compiler will reject programs that make the wrong assumptions about that process. The details of that nullification don't appear in this example, where the magic of type classes determines both the post-join type of each field and the right pretty-printing and parsing function for each of those types.</p> +view.urp + +<p>SQL views are also supported with a special declaration form, analogous to <tt>table</tt>. A multi-parameter type class <tt>fieldsOf</tt> is used to characterize places where both tables and views are allowed. For instance, the polymorphic function <tt>list</tt> shown here lists the contents of any table or view containing just a single <tt>int</tt> column named <tt>A</tt>.</p> + sum.urp <p>Metaprogramming is one of the most important facilities of Ur. This example shows how to write a function that is able to sum up the fields of records of integers, no matter which set of fields the particular record has.</p> |