Initial data commit

Task/Singly-linked-list-Traversal/Racket/singly-linked-list-traversal.rkt

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+#lang racket
+
+(define l (list 1 2 3))
+
+;; scan the list and collect a list of function results
+(map add1 l)
+
+;; scan the list and run some function on each element for its side-effect
+(for-each displayln l)
+
+;; scan a list and sum up its elements
+(foldl + 0 l)
+
+;; same as the above three, using a more modern syntax that is often
+;; more convenient
+(for/list ([x (in-list l)]) (add1 x))
+(for ([x (in-list l)]) (displayln x))
+(for/fold ([sum 0]) ([x (in-list l)]) (+ x sum))
+
+;; the same as the first, but make up a vector of results
+(for/vector ([x (in-list l)]) (add1 x))
+
+;; there is less support for mutable pairs, but it's still extensive
+;; enough to cover all the basics
+(require racket/mpair)
+(define ml (mlist 1 2 3))
+(mmap add1 ml)
+(mfor-each displayln ml)
+(for ([x (in-mlist ml)]) (displayln x))