From 9487a13344360c93bf63a7859a2336a074f43cae Mon Sep 17 00:00:00 2001
From: Jay McCarthy <jay.mccarthy@gmail.com>
Date: Thu, 14 Oct 2010 08:04:03 -0600
Subject: [PATCH] typed

---
 benford.rkt | 72 +++++++++++++++++++++++++++++++----------------------
 1 file changed, 42 insertions(+), 30 deletions(-)

diff --git a/benford.rkt b/benford.rkt
index c49c46e0..e6cae0a4 100644
--- a/benford.rkt
+++ b/benford.rkt
@@ -1,37 +1,49 @@
 #lang typed/racket
+(define-type Inputs (Listof Real))
+(define-type Digits (Listof Integer))
+(define-type Frequencies (Listof (Pair Integer Number)))
+
+(: freq (Digits -> Frequencies))
 (define (freq l)
   (define h (make-vector 10 0))
   (define tot
-    (for/fold ([tot 0]) ([e (in-list l)])
-      (dict-update! h e add1)
-      (add1 tot)))
-  (for/list ([(e c) (in-dict h)])
-    (cons e (/ c tot))))
-(define nums->digits
-  (curry map
-         (compose string->number
-                  string
-                  (λ (x) (string-ref x 0))
-                  number->string
-                  (λ (x) (if (x . < . 0) (- x) x)))))
-(define (sk l)
+    (for/fold:
+     : Integer ([tot : Integer 0]) 
+     ([e : Integer (in-list l)])
+     (vector-set! h e (add1 (vector-ref h e)))
+     (add1 tot)))
+  (for/list: : Frequencies
+   ([e : Integer (in-range 10)]
+    [c : Integer (in-vector h)])
+   (cons e (/ c tot))))
+
+(: nums->digits (Inputs -> Digits))
+(define (nums->digits l)
+  (for/list: : Digits
+   ([x : Real (in-list l)])
+   (define z (if (x . < . 0) (- x) x))
+   (- (char->integer
+       (string-ref (number->string z) 0))
+      (char->integer #\0))))
+
+(: benford (Inputs -> Frequencies))
+(define (benford l)
   (freq (nums->digits l)))
-(define (sort-em l)
-  (sort l >= #:key cdr))
 
 (equal?
- (sort-em
-  (sk (list 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.10
-            11 12 13 -14 15 16 17 18 19
-            21 -22 23 24 25 26 27 28
-            31 32 -33 34 35 36 37
-            41 42 43 44 45 46
-            51 -52 54 54 55
-            61 62 -63 64
-            71 -72 73
-            81 82
-            91)))
- (for/list ([i (in-range 10)])
-   (cons i
-         (/ (- 10 i)
-            (+ 10 9 8 7 6 5 4 3 2 1)))))
\ No newline at end of file
+ (benford 
+  (list 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.10
+        11 12 13 -14 15 16 17 18 19
+        21 -22 23 24 25 26 27 28
+        31 32 -33 34 35 36 37
+        41 42 43 44 45 46
+        51 -52 54 54 55
+        61 62 -63 64
+        71 -72 73
+        81 82
+        91))
+ (for/list: : Frequencies
+  ([i : Integer (in-range 10)])
+  (cons i
+        (/ (- 10 i)
+           (+ 10 9 8 7 6 5 4 3 2 1)))))
\ No newline at end of file