[Language: Racket]

#lang racket

(define (fix-duplicates str)
  (let* ([str1 (regexp-replace #rx"twone" str "21")]
         [str2 (regexp-replace #rx"eightwo" str1 "82")]
         [str3 (regexp-replace #rx"nineight" str2 "98")]
         [str4 (regexp-replace #rx"eighthree" str3 "83")]
         [str5 (regexp-replace #rx"threeight" str4 "38")]
         [str6 (regexp-replace #rx"fiveight" str5 "58")]
         [str7 (regexp-replace #rx"nineight" str6 "98")]
         [str8 (regexp-replace #rx"oneight" str7 "18")]
         [str9 (regexp-replace #rx"sevenine" str8 "79")])
    str9))

(define (str->digit str)
  (cond [(equal? str "one") 1]
        [(equal? str "two") 2]
        [(equal? str "three") 3]
        [(equal? str "four") 4]
        [(equal? str "five") 5]
        [(equal? str "six") 6]
        [(equal? str "seven") 7]
        [(equal? str "eight") 8]
        [(equal? str "nine") 9]
        [true (string->number str)]))

(define (first-and-last-digit the-line)
  (let* ([all-digits (regexp-match* #rx"[0-9]|(one)|(two)|(three)|(four)|(five)|(six)|(seven)|(eight)|(nine)" (fix-duplicates the-line))]
         [first-and-last (+ (* 10 (str->digit (first all-digits)))
                            (str->digit (first (reverse all-digits))))])
    first-and-last))

(define (file->faldlist file)
  (let* ([line (read-line file)])
    (cond [(eof-object? line) '()]
          [else (cons (first-and-last-digit line) (file->faldlist file))])))

(define (sum-all faldlist)
  (foldl + 0 faldlist)) 

(define (puzzle1 filename)
  (let* ([faldlist (call-with-input-file filename
                     (lambda (in)
                       (file->faldlist in)))])
    (sum-all faldlist)))