diff --git a/4.rkt b/4.rkt
index d5139dc..77932fc 100644
--- a/4.rkt
+++ b/4.rkt
@@ -5,79 +5,51 @@
 ;; solution for day 4
 
 ;; helper functions here
-(struct passport [byr iyr eyr hgt hcl ecl pid cid] #:transparent)
+(define-simple-macro (magic-struct name:id fld:id ...+)
+  #:with fld-names (format-id #'name "~a-fields" #'name)
+  (begin (struct name [fld ...] #:transparent)
+         (define fld-names (map symbol->string '(fld ...)))))
+
+(magic-struct passport byr iyr eyr hgt hcl ecl pid cid)
+
+(define (string->passport str)
+  (define pp (make-vector 8 #f))
+  (for ([part (in-list (string-split str))])
+    (match-define (list name val) (string-split part ":"))
+    (vector-set! pp (index-of passport-fields name) val))
+  (apply passport (vector->list pp)))
+
+(define pp-valid-part1?
+  (struct/c passport string? string? string? string? string? string? string? any/c))
 
 (define (part1 input)
-  (define pp-valid?
-    (struct/c passport string? string? string? string? string? string? string? any/c))
-  (for/sum ([pp (in-list input)] #:when (pp-valid? pp)) 1))
+  (stream-count pp-valid-part1? (in-list input)))
+
+(define (strlen/c num) (compose (=/c num) string-length))
+(define (string-integer-in low high) (compose (integer-in low high) string->number))
+(define (height/c hs)
+  (match hs
+    [(pregexp #px"([0-9]+)cm" (list _ h)) ((string-integer-in 150 193) h)]
+    [(pregexp #px"([0-9]+)in" (list _ h)) ((string-integer-in 59 76) h)]
+    [_ #f]))
+
+(define pp-valid-part2?
+  (and/c pp-valid-part1?
+         (struct/c passport
+                   (and/c (strlen/c 4) (string-integer-in 1920 2002))
+                   (and/c (strlen/c 4) (string-integer-in 2010 2020))
+                   (and/c (strlen/c 4) (string-integer-in 2020 2030))
+                   height/c
+                   (curry regexp-match #px"#[0-9a-f]{6}")
+                   (or/c "amb" "blu" "brn" "gry" "grn" "hzl" "oth")
+                   (and/c (strlen/c 9) (string-integer-in 0 999999999))
+                   any/c)))
 
 (define (part2 input)
-  (define ((strlen/c num) str)
-    (= (string-length str) num))
-
-  (define ((strnum-range/c low high) s)
-    (define sn (string->number s))
-    (and (number? sn)
-         (<= low sn high)))
-
-  (define (height/c hs)
-    (match hs
-      [(pregexp #px"([0-9]+)cm" (list _ h)) ((strnum-range/c 150 193) h)]
-      [(pregexp #px"([0-9]+)in" (list _ h)) ((strnum-range/c 59 76) h)]
-      [_ #f]))
-
-  (define (hcolor/c cs)
-    (match cs
-      [(pregexp #px"#[0-9a-f]{6}") #t]
-      [_ #f]))
-
-  (define (ecolor/c cs)
-    (match cs
-      [(or "amb" "blu" "brn" "gry" "grn" "hzl" "oth") #t]
-      [_ #f]))
-
-  (define pp-valid?
-    (struct/c passport
-              (and/c string? (strlen/c 4) (strnum-range/c 1920 2002))
-              (and/c string? (strlen/c 4) (strnum-range/c 2010 2020))
-              (and/c string? (strlen/c 4) (strnum-range/c 2020 2030))
-              (and/c string? height/c)
-              (and/c string? hcolor/c)
-              (and/c string? ecolor/c)
-              (and/c string? (strlen/c 9) (strnum-range/c 0 999999999))
-              any/c))
-  (for/sum ([pp (in-list input)] #:when (pp-valid? pp)) 1))
-
-(module+ test
-  (require rackunit)
-  ;; tests here
-  (displayln "no tests :("))
+  (stream-count pp-valid-part2? (in-list input)))
 
 (module+ main
-  (define input-lines (file->lines "inputs/4"))
-
-  (define input
-    (for/fold ([input (list (passport #f #f #f #f #f #f #f #f))]) ([line (in-list input-lines)])
-      (define pp (first input))
-      (cond
-        [(zero? (string-length line)) (cons (passport #f #f #f #f #f #f #f #f) input)]
-        [else
-         (define parts (string-split line " "))
-         (define new-pp
-           (for/fold ([new-pp pp]) ([part (in-list parts)])
-             (match-define (list name val) (string-split part ":"))
-             (match name
-               ["byr" (struct-copy passport new-pp [byr val])]
-               ["iyr" (struct-copy passport new-pp [iyr val])]
-               ["eyr" (struct-copy passport new-pp [eyr val])]
-               ["hgt" (struct-copy passport new-pp [hgt val])]
-               ["hcl" (struct-copy passport new-pp [hcl val])]
-               ["ecl" (struct-copy passport new-pp [ecl val])]
-               ["pid" (struct-copy passport new-pp [pid val])]
-               ["cid" (struct-copy passport new-pp [cid val])]
-               [_ (error "not shonks" line name val)])))
-         (cons new-pp (rest input))])))
+  (define input (map string->passport (string-split (file->string "inputs/4") "\n\n")))
 
   ;; part 1
   (answer 4 1 (part1 input))