From 1056081932314dbf339c97d6a7bda4fb927d4e39 Mon Sep 17 00:00:00 2001
From: Dimitri Lozeve <dimitri.lozeve@gmail.com>
Date: Tue, 18 Jul 2017 18:12:03 +0200
Subject: [PATCH] Update position and speed of all bodies

---
 src/Lib.hs | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/Lib.hs b/src/Lib.hs
index b5bfaef..8e7b63b 100644
--- a/src/Lib.hs
+++ b/src/Lib.hs
@@ -70,7 +70,17 @@ update dt (Body m pos speed) neighbours =
         newspeed = speed + dt *^ accel
         newpos = pos + dt *^ P newspeed
 
-
+-- Update all bodies with a timestep dt
+updateAll :: Double -> [Body] -> [Body]
+updateAll dt bodies = aux [] [] bodies
+  where
+    -- Cycles through all bodies, updates each one and stores it in
+    -- res. Each body already updated is moved to prev.
+    aux res prev [] = res
+    aux res prev (b:next) =
+          aux (newb:res) (b:prev) next
+          where newb = update dt b $ prev ++ next
+                    
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 -- EXAMPLES
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