transition: Move interpolation procedures to their relevant module.

* sly/color.scm (color-lerp): New procedure.
* sly/math.scm (make-lerp, lerp): New procedures.
* sly/math/vector.scm (vlerp): New procedure.
* sly/transition.scm (interpolator, number-interpolate,
  vector-interpolate, color-interpolate): Delete procedures.
  (guess-interpolator): Rewrite with 'match-lambda*'.

1 files changed, 13 insertions, 1 deletions

diff --git a/sly/math.scm b/sly/math.scm
index 4169ae4..923a93d 100644
--- a/sly/math.scm
+++ b/sly/math.scm
@@ -33,7 +33,8 @@
             cotan
             clamp
             linear-scale
-            half square))
+            half square
+            make-lerp lerp))
 
 ;; Dave was editing this module on Pi Approximation Day.
 ;;
@@ -110,3 +111,14 @@ actually less than MAX."
 
 (define (square x)
   (* x x))
+
+(define (make-lerp + *)
+  "Return a new procedure that accepts three arguments: A, B, and
+ALPHA.  The returned procedure uses the procedures + and * to linearly
+interpolate a value between A and B.  ALPHA should always be in the
+range [0, 1]."
+  (lambda (a b alpha)
+    (+ (* a (- 1 alpha))
+       (* b alpha))))
+
+(define lerp (make-lerp + *))