From 9502a9e98199d83c94e7b8df5decd82961343aa2 Mon Sep 17 00:00:00 2001
From: Sergiu Ivanov <sivanov@colimite.fr>
Date: Fri, 20 Mar 2020 01:19:14 +0100
Subject: [PATCH] utils: Add in-random.

---
 utils-tests.rkt | 19 +++++++++++++++++++
 utils.rkt       | 28 +++++++++++++++++++++++++++-
 2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/utils-tests.rkt b/utils-tests.rkt
index 1198428..c69fa25 100644
--- a/utils-tests.rkt
+++ b/utils-tests.rkt
@@ -129,3 +129,22 @@
 (test-case "Functions"
   (check-true (procedure-fixed-arity? not))
   (check-false (procedure-fixed-arity? +)))
+
+(test-case "Randomness"
+  (begin
+    (random-seed 0)
+    (check-equal? (stream->list (stream-take (in-random 100) 10))
+                  '(85 65 20 40 89 45 54 38 26 62))
+    (check-equal? (stream->list (stream-take (in-random 50 100) 10))
+                  '(75 59 82 85 61 85 59 64 75 53))
+    (check-equal? (stream->list (stream-take (in-random) 10))
+                  '(0.1656109603231493
+                    0.9680391127132195
+                    0.051518813640790355
+                    0.755901955353936
+                    0.5923534604277275
+                    0.5513340634474264
+                    0.7022057040731392
+                    0.48375400938578744
+                    0.7538961707172924
+                    0.01828428516237329))))
diff --git a/utils.rkt b/utils.rkt
index f286562..5bfd2bd 100644
--- a/utils.rkt
+++ b/utils.rkt
@@ -33,7 +33,11 @@
                [collect-by-key/sets (-> (listof any/c) (listof any/c) (values (listof any/c) (listof (set/c any/c))))]
 
                [ht-values/list->set (-> (hash/c any/c (listof any/c)) (hash/c any/c (set/c any/c)))]
-               [procedure-fixed-arity? (-> procedure? boolean?)])
+               [procedure-fixed-arity? (-> procedure? boolean?)]
+               [in-random (case-> (-> (stream/c (and/c real? inexact? (>/c 0) (</c 1))))
+                                  (-> (integer-in 1 4294967087) (stream/c exact-nonnegative-integer?))
+                                  (-> exact-integer? (integer-in 1 4294967087)
+                                      (stream/c exact-nonnegative-integer?)))])
  ;; Contracts
  (contract-out [variable-mapping? contract?]
                [string-variable-mapping? contract?]
@@ -329,3 +333,25 @@
 (define (procedure-fixed-arity? func)
   (match (procedure-arity func)
     [(arity-at-least _) #f] [arity #t]))
+
+
+;;; ==========
+;;; Randomness
+;;; ==========
+
+;;; Generates a stream of inexact random numbers.  The meaning of the
+;;; arguments is the same as for the function random:
+;;;
+;;; (in-randoms k) — a sequence of random exact integers in the range
+;;; 0 to k-1.
+;;;
+;;; (in-randoms min max) — a sequence of random exact integers the
+;;; range min to max-1.
+;;;
+;;; (in-randoms) — a sequence of random inexact numbers between
+;;; 0 and 1.
+(define in-random
+  (case-lambda
+    [() (for/stream ([i (in-naturals)]) (random))]
+    [(k) (for/stream ([i (in-naturals)]) (random k))]
+    [(min max) (for/stream ([i (in-naturals)]) (random min max))]))