From aab9846635f8a5a4671684d382aecb23102bb3bc Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Tue, 27 May 2014 21:22:09 -0400
Subject: Add scalar multiplication support to v* and remove vscale.

* 2d/vector2.scm (vscale): Delete it.
  (v*): Add support for scalar multiplication.
---
 2d/vector2.scm | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

(limited to '2d')

diff --git a/2d/vector2.scm b/2d/vector2.scm
index b85757a..c6beb57 100644
--- a/2d/vector2.scm
+++ b/2d/vector2.scm
@@ -22,6 +22,7 @@
 ;;; Code:
 
 (define-module (2d vector2)
+  #:use-module (ice-9 match)
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-9)
   #:export (<vector2>
@@ -34,7 +35,6 @@
             vector2-polar
             v+
             v*
-            vscale
             vmag
             vnorm
             vdot
@@ -66,7 +66,8 @@
   (add-vectors 0 0 vectors))
 
 (define (v* . vectors)
-  "Return the product of all VECTORS."
+  "Return the product of all VECTORS.  Alternatively, a single vector
+and a scalar can be specified to perform scalar multiplication."
   (define (multiply-vectors x y vectors)
     (cond ((null? vectors)
            (vector2 x y))
@@ -74,12 +75,10 @@
            (multiply-vectors (* x (vx (car vectors)))
                              (* y (vy (car vectors)))
                              (cdr vectors)))))
-  (multiply-vectors 1 1 vectors))
-
-(define (vscale v scalar)
-  "Multiply the vector V by a scalar value."
-  (vector2 (* (vx v) scalar)
-           (* (vy v) scalar)))
+  (match vectors
+    ((($ <vector2> x y) (? number? k))
+     (vector2 (* x k) (* y k)))
+    (_ (multiply-vectors 1 1 vectors))))
 
 (define (vmag v)
   "Return the magnitude of the vector V."
-- 
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