learning-racket

Some notes while using DrRacket.

Week 6

1. M06P33
   When writing the function insert, you don't have to re-sort the consumed list, since the list given to the function insert is already a sorted list. See the code below.

   (define (sort lon)
     (cond [(empty? lon) empty]
           [else (insert (first lon) (sort (rest lon)))]))
   
   (define (insert n slon)                                      ;; Note that "slon" stands for sorted list of num
    (cond [(empty? slon) (cons n empty)]
          [(<= n (first slon)) (cons n slon)]
          [else (cons (first slon) (insert n (rest slon)))]))
   

Week 9

• Stepping built-in functions: go straight to the end in one step.
• Always focus on what you want to produce. If you want to produce a function that consumes something and produces a two-argument function, then the code should be

(define (my-fn x)
  (lambda (x y) ...)      ;; here (x y) says the function it produces
                          ;; will consume two arguments, which meets our need.

• The first argument of foldr is a function that consumes two arguments (x and y, where x is the first item and y is the result of the rest).

Week 10

• (identity n) just produces the number/char/symbol itself.
  (identity 78) -> 78
  (identity 'a) -> 'a
  (identity "abc") -> "abc"