count-word-occurences.rkt

#lang racket

(define (increment-word hashmap words)
  (if (empty? words)
      hashmap
      (let ([word (car words)])
        (let ([count (hash-ref hashmap word 0)])
          (let ([hashmap-next (hash-set hashmap word (+ count 1))])
            (increment-word hashmap-next (cdr words)))))))

(define (process-line hashmap line)
  (let ([words (string-split (string-downcase line))])
    (increment-word hashmap words)))

(define (read-from-stdin)
  (define (read-from-stdin-it hashmap)
    (let ([line (read-line)])
      (if (eof-object? line)
          hashmap
          (read-from-stdin-it (process-line hashmap line)))))
  (let ([wc (hash)])
    (read-from-stdin-it wc)))

(define sorted (sort (hash->list (read-from-stdin))
                     >
                     #:key cdr))

(for ([pair sorted])
  (printf "~A ~A~%" (car pair) (cdr pair)))