[plt-scheme] append-map examples

Dan Friedman once shared a rule with me: when you use append-map, you are using the wrong data representation. 

Examples: 


On Apr 9, 2010, at 10:40 PM, Ryan Culpepper wrote:

> Skeptic . wrote:
>> Hi,
>> Does someone knows canonical/pedagogical exemples of append-map except other than flatten ?
> 
> Collect a list of all the X in a Y.
> 
> eg, the list of free variables in a lambda term

Free variables come in sets, not lists. 


> eg, the list of links in a web page (as xexpr or sxml)

Ditto.