From f420edc5eef6ab4bea68b3730edebdb91593759e Mon Sep 17 00:00:00 2001
From: Vincent St-Amour <stamourv@racket-lang.org>
Date: Sat, 25 Feb 2012 17:37:16 -0500
Subject: [PATCH] Add range to racket/list.

---
 collects/racket/list.rkt                   | 14 +++++++++++++-
 collects/scribblings/reference/pairs.scrbl | 16 ++++++++++++++++
 collects/tests/racket/list.rktl            | 16 ++++++++++++++++
 3 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/collects/racket/list.rkt b/collects/racket/list.rkt
index b5c8888049..ad085a9fa2 100644
--- a/collects/racket/list.rkt
+++ b/collects/racket/list.rkt
@@ -31,7 +31,8 @@
          ;; convenience
          append-map
          filter-not
-         shuffle)
+         shuffle
+         range)
 
 (define (first x)
   (if (and (pair? x) (list? x))
@@ -362,3 +363,14 @@
 
 (define (argmin f xs) (mk-min < 'argmin f xs))
 (define (argmax f xs) (mk-min > 'argmax f xs))
+
+;; similar to in-range, but returns a list
+(define range
+  (case-lambda
+    [(end)       (range 0     end 1)]
+    [(start end) (range start end 1)]
+    [(start end step)
+     (unless (real? start) (raise-type-error 'range "real-number" start))
+     (unless (real? end)   (raise-type-error 'range "real-number" end))
+     (unless (real? step)  (raise-type-error 'range "real-number" step))
+     (for/list ([i (in-range start end step)]) i)]))
diff --git a/collects/scribblings/reference/pairs.scrbl b/collects/scribblings/reference/pairs.scrbl
index 2e677f1d8c..23131bfa39 100644
--- a/collects/scribblings/reference/pairs.scrbl
+++ b/collects/scribblings/reference/pairs.scrbl
@@ -1012,6 +1012,22 @@ the result of @racket[proc]. Signals an error on an empty list.
 (argmax car '((3 pears) (3 oranges)))
 ]}
 
+@defproc*[([(range [end real?]) list?]
+           [(range [start real?] [end real?] [step real? 1]) list?])]{
+  Returns a list of numbers starting at @racket[start] and whose successive
+  elements are computed by adding @racket[step] to their predecessor until
+  @racket[end] (excluded) is reached.
+  If no starting point is provided, @racket[0] is used. If no @racket[step]
+  argument is provided, @racket[1] is used.
+@mz-examples[#:eval list-eval
+(range 10)
+(range 10 20)
+(range 20 40 2)
+(range 20 10 -1)
+(range 10 15 1.5)
+]}
+
+
 @close-eval[list-eval]
 
 @; ----------------------------------------
diff --git a/collects/tests/racket/list.rktl b/collects/tests/racket/list.rktl
index c29a4c4335..07de397754 100644
--- a/collects/tests/racket/list.rktl
+++ b/collects/tests/racket/list.rktl
@@ -378,7 +378,23 @@
   (err/rt-test (argmax (lambda (x) x) (list +i)) (check-regs #rx"argmax" #rx"procedure that returns real numbers"))
   (err/rt-test (argmax (lambda (x) x) (list)) (check-regs #rx"argmax" #rx"non-empty list")))
 
+;; ---------- range ----------
 
+(let ()
+  (test '(0 1 2 3) range 4)
+  (test '() range 0)
+  (test '(0 1 2 3 4 5 6 7) range 8)
+  (test '() range 3 2)
+  (test '(3) range 3 2 -1)
+  (test '(3 4 5 6 7 8) range 3 9)
+  (test '(3 5 7) range 3 9 2)
+  (test '(3 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5) range 3 9 0.5)
+  (test '(9 7 5) range 9 3 -2)
+  (test '(0 1 2 3 4 5 6 7 8 9) range 10)
+  (test '(10 11 12 13 14 15 16 17 18 19) range 10 20)
+  (test '(20 22 24 26 28 30 32 34 36 38) range 20 40 2)
+  (test '(20 19 18 17 16 15 14 13 12 11) range 20 10 -1)
+  (test '(10 11.5 13.0 14.5) range 10 15 1.5))
 
 ;; ---------- check no collisions with srfi/1 ----------
 (test (void)