Optimization: split LMove-and-Wait into two SMoves (#6)

Author: Minoru

package.yaml

@@ -45,7 +45,7 @@ executables:
 
 tests:
   icfpc2018-test:
-    main:                Spec.hs
+    main:                Test.hs
     source-dirs:         test
     ghc-options:
     - -threaded

src/Optimizations.hs

@@ -0,0 +1,22 @@
+-- | Optimizations for sequences of commands.
+--
+-- Each optimizations replaces first occurrence of a pattern with an optimized
+-- version.  It's up to you to figure out if the result is better than the
+-- input, and if you should re-run optimizations to find new occurrences of
+-- patterns.
+module Optimizations where
+
+import Trace
+
+-- | Turns [LMove a b, Wait] into [SMove a, SMove b]
+--
+-- The latter consumes 4 less energy points than the former.
+--
+-- Note: it doesn't make sense to split [LMove a b] into two SMoves because the
+-- extra step will consume 3 R³ energy points, which is detrimental for any
+-- R greater than one.
+splitLMove :: [Command] -> [Command]
+splitLMove [] = []
+splitLMove ((LMove a b):Wait:cmds) =
+  (SMove (fromShortLinDiff a)) : (SMove (fromShortLinDiff b)) : cmds
+splitLMove (cmd:cmds) = cmd : (splitLMove cmds)

src/Trace.hs

@@ -167,6 +167,12 @@ instance Coded Command where
 
         | otherwise = error "Command.decode: invalid input"
 
+-- | Converts short linear difference into a long linear difference.
+--
+-- This conversion is valid since any short linear difference satisfies
+-- mlen(ld) ≤ 5, which also satisfies LongLinDiff's predicate of mlen(ld) ≤ 15.
+fromShortLinDiff :: ShortLinDiff -> LongLinDiff
+fromShortLinDiff (ShortLinDiff axis diff) = LongLinDiff axis diff
 
 encodeL :: Coded a => a -> L.ByteString
 encodeL x = runPutL . runEncode $ encode x >> flush

test/Test.hs

@@ -0,0 +1,10 @@
+import Test.Tasty
+
+import TestSpec
+import TestOptimizations
+
+main :: IO ()
+main = defaultMain tests
+
+tests :: TestTree
+tests = testGroup "Tests" [specExamples, codec, optimizations]

test/TestOptimizations.hs

@@ -0,0 +1,34 @@
+module TestOptimizations where
+
+import Test.Tasty
+import Test.Tasty.HUnit
+
+import Optimizations
+import Trace
+
+optimizations :: TestTree
+optimizations = testGroup "Optimizations" [testSplitLMove]
+
+testSplitLMove :: TestTree
+testSplitLMove = testGroup "splitLMove"
+  [
+    testCase "Empty input" $ splitLMove [] @?= []
+
+  , testCase "Unoptimal input" $
+      let
+        a = ShortLinDiff X 3
+        a' = fromShortLinDiff a
+        b = ShortLinDiff Z (-1)
+        b' = fromShortLinDiff b
+      in splitLMove [LMove a b, Wait] @?= [SMove a', SMove b']
+
+  , testCase "Only first occurrence is optimized" $
+      let
+        a = ShortLinDiff X 3
+        a' = fromShortLinDiff a
+        b = ShortLinDiff Z (-1)
+        b' = fromShortLinDiff b
+      in
+        splitLMove [LMove a b, Wait, LMove a b, Wait]
+        @?= [SMove a', SMove b', LMove a b, Wait]
+  ]

test/Spec.hs test/TestSpec.hstest/Spec.hs renamed to test/TestSpec.hs

@@ -1,5 +1,10 @@
 {-# LANGUAGE BinaryLiterals #-}
 
+module TestSpec (
+  specExamples,
+  codec
+) where
+
 import Test.Tasty
 import Test.Tasty.HUnit
 
@@ -15,12 +20,6 @@ assert :: String -> Bool -> IO ()
 assert _ True = return ()
 assert message False = fail message
 
-main :: IO ()
-main = defaultMain tests
-
-tests :: TestTree
-tests = testGroup "Tests" [specExamples, codec]
-
 specExamples :: TestTree
 specExamples = testGroup "Specification examples"
   [