Mercurial > urweb
comparison demo/prose @ 416:679b2fbbd4d0
Counter demo
| author | Adam Chlipala <adamc@hcoop.net> |
|---|---|
| date | Thu, 23 Oct 2008 11:59:48 -0400 |
| parents | 6a0e54400805 |
| children | e0e9e9eca1cb |
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| 415:777317e8b2ae | 416:679b2fbbd4d0 |
|---|---|
| 42 | 42 |
| 43 rec.urp | 43 rec.urp |
| 44 | 44 |
| 45 <p>Crafting webs of interlinked pages is easy, using recursion.</p> | 45 <p>Crafting webs of interlinked pages is easy, using recursion.</p> |
| 46 | 46 |
| 47 counter.urp | |
| 48 | |
| 49 <p>It is also easy to pass state around via functions, in the style commonly associated with "continuation-based" web servers. As is usual for such systems, all state is stored on the client side. In this case, it is encoded in URLs.</p> | |
| 50 | |
| 51 <p>In the implementation of <tt>Counter.counter</tt>, we see the notation <tt>{[...]}</tt>, which uses type classes to inject values of different types (<tt>int</tt> in this case) into XML. It's probably worth stating explicitly that XML fragments <i>are not strings</i>, so that the type-checker will enforce that our final piece of XML is valid.</p> | |
| 52 | |
| 47 form.urp | 53 form.urp |
| 48 | 54 |
| 49 <p>Here we see a basic form. The type system tracks which form inputs we include, and it enforces that the form handler function expects a record containing exactly those fields, with exactly the proper types.</p> | 55 <p>Here we see a basic form. The type system tracks which form inputs we include, and it enforces that the form handler function expects a record containing exactly those fields, with exactly the proper types.</p> |
| 50 | |
| 51 <p>In the implementation of <tt>handler</tt>, we see the notation <tt>{[...]}</tt>, which uses type classes to inject values of different types (<tt>string</tt> and <tt>bool</tt> in this case) into XML. It's probably worth stating explicitly that XML fragments <i>are not strings</i>, so that the type-checker will enforce that our final piece of XML is valid.</p> | |
| 52 | 56 |
| 53 listShop.urp | 57 listShop.urp |
| 54 | 58 |
| 55 <p>This example shows off algebraic datatypes, parametric polymorphism, and functors.</p> | 59 <p>This example shows off algebraic datatypes, parametric polymorphism, and functors.</p> |
| 56 | 60 |