>> Would it be possible to extend the sort function to allow for multiple
>> keys to facilitate sorting lists of lists or lists of structs.
The sort function should accommodate this by providing a custom
comparator as the second (optional) argument to it.
When building custom comparators, you might find the "datum-order"
function from the data/order library to be helpful, as its definition
knows how to deal with lists of comparable things:
http://docs.racket-lang.org/data/Orders_and_Ordered_Dictionaries.html#(def._((lib._data/order..rkt)._datum-order))
For example:
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
#lang racket
(require data/order)
(struct person (name age) #:transparent)
(define p1 (person "Danny" 33))
(define p2 (person "Grandma" 94))
(define p3 (person "Grandma" 92))
(define (my-less-than x y)
(eq? '< (datum-order x y)))
(sort (list p1 p2 p3) my-less-than)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
It's a little unfortunate that there's a slight impedance mismatch
between what datum-order provides and what sort expects; the
my-less-than function in the example adapts the output of datum-order
so it can be used with sort.
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