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| author |  Adam Chlipala <adamc@hcoop.net> | 2009-03-10 13:46:45 -0400 |
|---|---|---|
| committer | Adam Chlipala <adamc@hcoop.net> | 2009-03-10 13:46:45 -0400 |
| commit | b3bfa064636a8507e0fe83779791dbbee6f15c38 (patch) | |
| tree | 6fb9724c03715a330a6ee10a1e9b09340e1f6d0b /demo/prose | |
| parent | 18c2f489867bf282c49346eb090b22e41ec5f67a (diff) | |
Prose for ListEdit
Diffstat (limited to 'demo/prose')
| -rw-r--r-- | demo/prose | 8 |
1 files changed, 8 insertions, 0 deletions
@@ -197,3 +197,11 @@ react.urp <p>Most client-side JavaScript programs modify page contents imperatively, but Ur/Web is based on functional-reactive programming instead. Programs allocate data sources and then describe the page as a pure function of those data sources. When the sources change, the page changes automatically.</p> <p>Here's an example where a button modifies a data source that affects some text on the page. The affected portion of the page is indicated with the pseudo-HTML tag <tt>dyn</tt>, whose <tt>signal</tt> attribute specifies one of these pure functions over mutable sources. A source containing data of type <tt>t</tt> has type <tt>source t</tt> and is created with the <tt>source</tt> operation within the <tt>transaction</tt> monad. Functions over sources are represented in the monad <tt>signal</tt>. Like in Haskell, we overload monad notations, so that the same return and bind operators can be used to write signals and transactions. The <tt>signal</tt> function coerces a source to a signal.</p> + +listEdit.urp + +<p>This is a more involved functional-reactive example, involving recursive data structures that contain sources. We build a list editor similar to the one from the <tt>ListShop</tt> example, but with all editing happening on the client side.</p> + +<p>The central data structure is the <tt>rlist</tt>, a list whose individual elements are sources, enabling fine-grained mutation. Every rlist is either nil or is a cons cell made up of a source for a string data element, another source to serve as a scratchpad for GUI-based edits to the data element, and a final source that stores the remainder of the list.</p> + +<p>The main program provides operations to append to a list and to edit the data stored at any cell of the list. Append is implemented by maintaining a source <tt>head</tt>, which points to the first list element; and a source <tt>tailP</tt>, which points to a <tt>source rlist</tt> where we should place the next appended node.</p> |