Hi, On 07/11/2018 02:46 PM, Vanessa McHale wrote:
#2: enumerate all strings on an alphabet (this uses laziness!)
allStrings :: [a] -> [[a]] allStrings = sequence <=< (inits . repeat)
Neat! I find the following alternative appealing too, as it in essence just states a recursive equation that says what it means for a list to be a list of all strings over the given alphabet: allStrings alphabet = xss where xss = [] : [ x : xs | xs <- xss, x <- alphabet ] (Admittedly, one has to be careful with the ordering of the generators, or the order in which the strings are enumerated becomes less useful.) This capability of declaratively stating an equation that characterises the sought answer is another perspective on why techniques like dynamic programming is such a great fit for lazy languages, as pointed out by Jake. One of my favourite examples is finding a minimal length triangulation of a polygon where an elegant solution is obtained by just transliterating the defining equations from a classic textbook on data structures and algorithms (Aho, Hopcroft, Ullman 1983). Attribute grammar evaluation is another great application of laziness in a similar vein. Best, /Henrik This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please contact the sender and delete the email and attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. Email communications with the University of Nottingham may be monitored where permitted by law.