For instance, every HTML-generating function you write is going to take the arguments and entity and then will contain calls to with-http-response, with-http-response, and—if you’re going to use FOO to generate HTML—with-html-output. Then, in functions that need to get at query parameters, there will be a bunch of calls to request-query-value and then more code to convert the string returned to whatever type you actually want. Finally, you need to remember to the function.

To reduce the amount of boilerplate you have to write, you can write a small framework on top of AllegroServe to make it easier to define functions that handle requests for a particular URL.

where the body is the code to emit the HTML of the page. It’ll be wrapped in a call to FOO’s html macro, so for simple pages it might contain nothing but s-expression HTML.

Within the body, the query parameter variables will be bound to values of query parameters with the same name or from a cookie. In the simplest case, a query parameter’s value will be the string taken from the query parameter or post data field of the same name. If the query parameter is specified with a list, you can also specify an automatic type conversion, a default value, and whether to look for and save the value of the parameter in a cookie. The complete syntax for a query-parameter is as follows:

The name of the cookie used depends on the value of stickiness: with a value of :global, the cookie will be named the same as the parameter. Thus, different functions that use globally sticky parameters with the same name will share the value. If stickiness is :package, then the cookie name is constructed from the name of the parameter and the package of the function’s name; this allows functions in the same package to share values but not have to worry about stomping on parameters of functions in other packages. Finally, a parameter with a stickiness value of :local will use a cookie made from the name of the parameter, the package of the function name, and the function name, making it unique to that function.

For instance, you can use define-url-function to replace the previous eleven-line definition of random-page with this five-line version: