diff --git a/ChangeLog.md b/ChangeLog.md
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--- /dev/null
+++ b/ChangeLog.md
@@ -0,0 +1,3 @@
+# Changelog for HappyTree
+
+## Unreleased changes
diff --git a/HappyTree.cabal b/HappyTree.cabal
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--- /dev/null
+++ b/HappyTree.cabal
@@ -0,0 +1,72 @@
+-- This file has been generated from package.yaml by hpack version 0.20.0.
+--
+-- see: https://github.com/sol/hpack
+--
+-- hash: ca077430f4b90fc7a4a71fa0738c6711a609f4b20ff2f746b4e91c7aa4cc897c
+
+name:           HappyTree
+version:        0.2018.1.5
+description:    Please see the README on Github at <https://github.com/MarisaKirisame/HappyTree#readme>
+homepage:       https://github.com/MarisaKirisame/HappyTree#readme
+bug-reports:    https://github.com/MarisaKirisame/HappyTree/issues
+author:         Marisa Kirisame
+maintainer:     lolisa@marisa.moe
+copyright:      2018 Marisa Kirisame
+license:        BSD3
+license-file:   LICENSE
+build-type:     Simple
+cabal-version:  >= 1.10
+
+extra-source-files:
+    ChangeLog.md
+    README.md
+
+source-repository head
+  type: git
+  location: https://github.com/MarisaKirisame/HappyTree
+
+library
+  hs-source-dirs:
+      src
+  ghc-options: -Wno-partial-type-signatures
+  build-depends:
+      base >=4.7 && <5
+    , constraints ==0.9.1
+    , generics-sop ==0.3.1.0
+    , singletons ==2.3.1
+  exposed-modules:
+      Lib
+  other-modules:
+      Paths_HappyTree
+  default-language: Haskell2010
+
+executable HappyTree-exe
+  main-is: Main.hs
+  hs-source-dirs:
+      app
+  ghc-options: -threaded -rtsopts -with-rtsopts=-N -Wno-partial-type-signatures
+  build-depends:
+      HappyTree
+    , base >=4.7 && <5
+    , constraints ==0.9.1
+    , generics-sop ==0.3.1.0
+    , singletons ==2.3.1
+  other-modules:
+      Paths_HappyTree
+  default-language: Haskell2010
+
+test-suite HappyTree-test
+  type: exitcode-stdio-1.0
+  main-is: Spec.hs
+  hs-source-dirs:
+      test
+  ghc-options: -threaded -rtsopts -with-rtsopts=-N
+  build-depends:
+      HappyTree
+    , base >=4.7 && <5
+    , constraints ==0.9.1
+    , generics-sop ==0.3.1.0
+    , singletons ==2.3.1
+  other-modules:
+      Paths_HappyTree
+  default-language: Haskell2010
diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,30 @@
+Copyright Marisa Kirisame (c) 2018
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of Marisa Kirisame nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/README.md b/README.md
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--- /dev/null
+++ b/README.md
@@ -0,0 +1,1 @@
+# HappyTree
diff --git a/Setup.hs b/Setup.hs
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--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/app/Main.hs b/app/Main.hs
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--- /dev/null
+++ b/app/Main.hs
@@ -0,0 +1,6 @@
+module Main where
+
+import Lib
+
+main :: IO ()
+main = someFunc
diff --git a/src/Lib.hs b/src/Lib.hs
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--- /dev/null
+++ b/src/Lib.hs
@@ -0,0 +1,119 @@
+{-# LANGUAGE 
+  DataKinds,
+  TypeFamilies,
+  TemplateHaskell,
+  PolyKinds,
+  ExistentialQuantification,
+  ScopedTypeVariables,
+  UndecidableInstances,
+  TypeOperators,
+  UndecidableSuperClasses,
+  GADTs,
+  PartialTypeSignatures
+#-}
+
+module Lib where
+
+import Data.Singletons.Prelude
+import Data.Void
+import Data.Singletons.TH
+import qualified Generics.SOP as SOP
+import Data.Constraint
+import Data.Proxy
+
+someFunc :: IO ()
+someFunc = putStrLn "someFunc"
+
+$(singletons [d|
+  revAppend :: [a] -> [a] -> [a]
+  revAppend [] x = x
+  revAppend (x:xs) n = revAppend xs (x:n) 
+  takeElemAux :: [a] -> [a] -> [(a, [a])]
+  takeElemAux l [] = []
+  takeElemAux l (r:rs) = (r, revAppend l rs) : takeElemAux (r:l) rs 
+  takeElem :: [a] -> [(a, [a])]
+  takeElem = takeElemAux []
+ |])
+
+class (SplitCode a ~ SOP.Code a, SOP.Generic a) => SplitStructure a where
+  type SplitCode a :: [[*]]
+  type SplitCode a = SOP.Code a
+  splitStructureFrom :: a -> SOP.SOP SOP.I (SplitCode a)
+  splitStructureFrom = SOP.from
+  splitStructureTo :: SOP.SOP SOP.I (SplitCode a) -> a
+
+class Ord a => SplitOrd a
+
+newtype SplitStructureOnAux dt b r a = SplitStructureOnAux { runSplitStructureOnAux :: dt (r :++ a) b }
+
+newtype SplitStructureOn dt b a =
+  SplitStructureOn { runSplitStructureOn :: (Dict (SplitStructure (Fst a)), SOP.NP (SplitStructureOnAux dt b (Snd a)) (SplitCode (Fst a))) }
+
+newtype SplitOrderOn dt b a = SplitOrderOn { runSplitOrderOn :: (Dict (SplitOrd (Fst a)), (Fst a), dt (Fst a:Snd a) b, dt (Snd a) b, dt (Fst a:Snd a) b) }
+
+data DecisionTree (a :: [*]) (b :: *) =
+  Leaf (SOP.NP SOP.I a -> b) |
+  SplitOnStructure (SOP.NS (SplitStructureOn DecisionTree b) (TakeElem a)) |
+  SplitOnOrd (SOP.NS (SplitOrderOn DecisionTree b) (TakeElem a))
+
+newtype TakeElemTypeAux a = TakeElemTypeAux { runTakeElemTypeAux :: (Fst a, SOP.NP SOP.I (Snd a)) }
+
+type family TakeElemAuxType (a :: [*]) (b :: [*]) :: *
+type instance TakeElemAuxType a b = SOP.NP TakeElemTypeAux (TakeElemAux a b)
+
+type family TakeElemType (a :: [*]) :: *
+type instance TakeElemType a = TakeElemAuxType '[] a
+
+revAppendDT :: SOP.NP f a -> SOP.NP f b -> SOP.NP f (RevAppend a b)
+revAppendDT SOP.Nil x = x
+revAppendDT (x SOP.:* y) z = revAppendDT y (x SOP.:* z)
+
+takeElemAuxDT :: SOP.NP SOP.I a -> SOP.NP SOP.I b -> TakeElemAuxType a b
+takeElemAuxDT _ SOP.Nil = SOP.Nil
+takeElemAuxDT x (SOP.I y SOP.:* z) = TakeElemTypeAux (y, revAppendDT x z) SOP.:* takeElemAuxDT (SOP.I y SOP.:* x) z
+
+dictSList :: SOP.SList a -> Dict (SOP.SListI a)
+dictSList SOP.SNil = Dict
+dictSList SOP.SCons = Dict
+
+sListCons :: Proxy a -> SOP.SList b -> SOP.SList (a:b)
+sListCons _ x = dictSList x `withDict` SOP.SCons
+
+unSListCons :: forall (a :: [k]) . SOP.SList (_:a) -> SOP.SList a
+unSListCons SOP.SCons = SOP.sList
+
+takeElemAuxDTSingAux :: SOP.SList (a:as) -> Proxy a
+takeElemAuxDTSingAux _ = Proxy
+
+takeElemAuxDTSing :: SOP.SList a -> SOP.SList b -> SOP.SList (TakeElemAux a b)
+takeElemAuxDTSing _ SOP.SNil = SOP.SNil
+takeElemAuxDTSing x y@SOP.SCons =
+  dictSList (takeElemAuxDTSing (sListCons (takeElemAuxDTSingAux y) x) (unSListCons y)) `withDict` SOP.SCons
+
+takeElemDT :: SOP.NP SOP.I a -> TakeElemType a
+takeElemDT = takeElemAuxDT SOP.Nil
+
+sopAppend :: SOP.NP f a -> SOP.NP f b -> SOP.NP f (a :++ b)
+sopAppend SOP.Nil x = x
+sopAppend (x SOP.:* y) z = x SOP.:* sopAppend y z
+
+npToSList :: SOP.NP f a -> SOP.SList a
+npToSList SOP.Nil = SOP.SNil
+npToSList (_ SOP.:* x) = sListCons Proxy (npToSList x)
+
+eval :: DecisionTree a b -> SOP.NP SOP.I a -> b
+eval (Leaf f) x = f x
+eval (SplitOnStructure f) x =
+  dictSList (takeElemAuxDTSing SOP.SNil (npToSList x)) `withDict`
+  (SOP.hcollapse $ SOP.hzipWith
+    (\(TakeElemTypeAux (a, b)) (SplitStructureOn (Dict, d)) ->
+      let SOP.SOP e = splitStructureFrom a in
+      SOP.K (SOP.hcollapse $ SOP.hzipWith (\(SplitStructureOnAux f) g -> SOP.K (eval f (sopAppend b g))) d e)) (takeElemDT x) f)
+eval (SplitOnOrd f) x =
+  dictSList (takeElemAuxDTSing SOP.SNil (npToSList x)) `withDict`
+  (SOP.hcollapse $ SOP.hzipWith
+    (\(TakeElemTypeAux (a, b)) (SplitOrderOn (Dict, d, e, f, g)) ->
+      SOP.K (case a `compare` d of
+               LT -> eval e (SOP.I a SOP.:* b)
+               EQ -> eval f b
+               GT -> eval g (SOP.I a SOP.:* b))) (takeElemDT x) f)
diff --git a/test/Spec.hs b/test/Spec.hs
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--- /dev/null
+++ b/test/Spec.hs
@@ -0,0 +1,2 @@
+main :: IO ()
+main = putStrLn "Test suite not yet implemented"