AoC'21, day 8, first problem rvc

The sub computer running a four-digit display, seven segments per digit, has garbled its output signals by running them through a permutation. The first problem involves counting the number of digit encodings uniquely determined by the number of segments used.

 $ cat 08a.rkt 
 #lang racket 
  
  
 (provide 
   example-input 
   read-input 
   ) 
  
  
 (require 
   (prefix-in aoc: "aoc.rkt") 
   (prefix-in utl: "../scheme/utl.rkt") 
   ) 
  
  
 (define (aoc08a . args) 
  
   ; Return the number of times the digits 1, 4, 7 or 8 appear in 
   ; the given display input-output.  If no display i-o is given, 
   ; use the contest problem input; otherwise assume the argument 
   ; is the string representation of a problem input. 
  
   (length 
     (filter 
       (lambda (s) (member (length s) '(2 3 4 7))) 
       (utl:flatten-to-n (map cadr (apply read-input args)) 1)))) 
  
  
 (define  (read-input . arg) 
  
   ; Return the given display input-output.  If no argument is 
   ; given, use the contest problem input; otherwise assume the 
   ; argument is the string representation of a problem input. 
  
  
   (define (explode-string-list l) 
     (map (lambda (s) (string->list s)) l)) 
    
  
   (define (split-line l) 
     (map 
       explode-string-list 
       (list (take l 10) (drop l 11)))) 
  
  
   (map 
     split-line 
     (car (aoc:aoc-read-input (if (null? arg) 8 (car arg)))))) 
  
  
 (define example-input (aoc:strings->string 
   "be cfbegad cbdgef fgaecd cgeb fdcge agebfd fecdb fabcd edb | fdgacbe cefdb cefbgd gcbe" 
   "edbfga begcd cbg gc gcadebf fbgde acbgfd abcde gfcbed gfec | fcgedb cgb dgebacf gc" 
   "fgaebd cg bdaec gdafb agbcfd gdcbef bgcad gfac gcb cdgabef | cg cg fdcagb cbg" 
   "fbegcd cbd adcefb dageb afcb bc aefdc ecdab fgdeca fcdbega | efabcd cedba gadfec cb" 
   "aecbfdg fbg gf bafeg dbefa fcge gcbea fcaegb dgceab fcbdga | gecf egdcabf bgf bfgea" 
   "fgeab ca afcebg bdacfeg cfaedg gcfdb baec bfadeg bafgc acf | gebdcfa ecba ca fadegcb" 
   "dbcfg fgd bdegcaf fgec aegbdf ecdfab fbedc dacgb gdcebf gf | cefg dcbef fcge gbcadfe" 
   "bdfegc cbegaf gecbf dfcage bdacg ed bedf ced adcbefg gebcd | ed bcgafe cdgba cbgef" 
   "egadfb cdbfeg cegd fecab cgb gbdefca cg fgcdab egfdb bfceg | gbdfcae bgc cg cgb" 
   "gcafb gcf dcaebfg ecagb gf abcdeg gaef cafbge fdbac fegbdc | fgae cfgab fg bagce" 
   )) 
  
  
 (define example-output 26) 
  
  
 (module+ main 
   (aoc08a) 
   ) 
  
  
 (module+ test 
  
   (require rackunit) 
  
   (for-each 
     (lambda (p) (check-equal? (aoc08a (car p)) (cdr p))) 
     '(("be cfbegad cbdgef fgaecd cgeb fdcge agebfd fecdb fabcd edb | fdgacbe cefdb cefbgd gcbe" . 2) 
       ("edbfga begcd cbg gc gcadebf fbgde acbgfd abcde gfcbed gfec | fcgedb cgb dgebacf gc" . 3) 
       ("fgaebd cg bdaec gdafb agbcfd gdcbef bgcad gfac gcb cdgabef | cg cg fdcagb cbg" . 3) 
       ("fbegcd cbd adcefb dageb afcb bc aefdc ecdab fgdeca fcdbega | efabcd cedba gadfec cb" . 1) 
       ("aecbfdg fbg gf bafeg dbefa fcge gcbea fcaegb dgceab fcbdga | gecf egdcabf bgf bfgea" . 3) 
       ("fgeab ca afcebg bdacfeg cfaedg gcfdb baec bfadeg bafgc acf | gebdcfa ecba ca fadegcb" . 4) 
       ("dbcfg fgd bdegcaf fgec aegbdf ecdfab fbedc dacgb gdcebf gf | cefg dcbef fcge gbcadfe" . 3) 
       ("bdfegc cbegaf gecbf dfcage bdacg ed bedf ced adcbefg gebcd | ed bcgafe cdgba cbgef" . 1) 
       ("egadfb cdbfeg cegd fecab cgb gbdefca cg fgcdab egfdb bfceg | gbdfcae bgc cg cgb" . 4) 
       ("gcafb gcf dcaebfg ecagb gf abcdeg gaef cafbge fdbac fegbdc | fgae cfgab fg bagce" . 2))) 
  
   (check-equal? (aoc08a example-input) example-output) 
   (check-equal? (aoc08a) 416) 
   ) 
  
 $ raco test 08a.rkt  
 raco test: (submod "08a.rkt" test) 
 12 tests passed 
  
 $