diff --git a/day01/default.nix b/day01/default.nix
index c99d67c..d20f196 100644
--- a/day01/default.nix
+++ b/day01/default.nix
@@ -29,4 +29,4 @@ in pkgs.writeText "answers" ''
 
   Task2:
     ${answer2}
-''
\ No newline at end of file
+''
diff --git a/day02/default.nix b/day02/default.nix
index 97ee6f3..f7fd532 100644
--- a/day02/default.nix
+++ b/day02/default.nix
@@ -10,11 +10,13 @@ let
   ];
 
   inherentValue = x: { A = 1; B = 2; C = 3; }.${x};
+
   comparativeValue = { they, you }: if they == you then 3 else
                                     if (they == "A" && you == "B")
                                     || (they == "B" && you == "C")
                                     || (they == "C" && you == "A") then 6 else
                                     0;
+
   score = match: comparativeValue match + inherentValue match.you;
 
   equalizeValueType = x: { X = "A"; Y = "B"; Z = "C"; }.${x};
@@ -31,7 +33,9 @@ let
     Y = { A = 1; B = 2; C = 3; };
     Z = { A = 2; B = 3; C = 1; };
   }.${you}.${they};
+
   comparativeValue2 = x: { X = 0; Y = 3; Z = 6; }.${x};
+
   score2 = match: comparativeValue2 match.you + inherentValue2 match;
 
   answer2 = pipe guide [
@@ -46,4 +50,4 @@ in pkgs.writeText "answers" ''
 
   Task2:
     ${answer2}
-''
\ No newline at end of file
+''
diff --git a/day03/default.nix b/day03/default.nix
index d9c56ac..df9b9f1 100644
--- a/day03/default.nix
+++ b/day03/default.nix
@@ -1,8 +1,10 @@
-{ pkgs, lib }:
+{ pkgs, lib, AoCLib, ... }:
 
 with lib;
 
 let
+  inherit (AoCLib) transformRange chunksOf;
+
   compartments = pipe (fileContents ./input.txt) [
     (splitString "\n")
   ];
@@ -11,15 +13,15 @@ let
     c1 = substring 0 ((stringLength s) / 2) s;
     c2 = substring ((stringLength s) / 2) (stringLength s) s;
   };
+
   charsToSet = s: foldl (set: c: set // { ${c} = true; }) { } (stringToCharacters s);
+
   getCommonChar = { c1, c2 }:
     findSingle
       (c: c2.${c} or false)
       "Error: no common chars"
       "Error: multiple chars"
       (attrNames c1);
-  mapRange = min: max: f: i: if min <= i && i < max then f i else i;
-  transformRange = min: max: offset: i: mapRange min max (x: x + offset) i;
 
   charValue = c: pipe c [
     lib.strings.charToInt
@@ -36,14 +38,12 @@ let
     toString
   ];
 
-  chunksOf = n: l: if length l <= n
-                     then [l]
-                     else [(take n l)] ++ (chunksOf n (drop n l));
   toA123 = l: {
     a1 = elemAt l 0;
     a2 = elemAt l 1;
     a3 = elemAt l 2;
   };
+
   getCommonChar2 = { a1, a2, a3 }:
     findSingle
       (c: a2.${c} or false && a3.${c} or false)
diff --git a/day04/default.nix b/day04/default.nix
index dd61647..fb55c5a 100644
--- a/day04/default.nix
+++ b/day04/default.nix
@@ -1,4 +1,4 @@
-{ pkgs, lib }:
+{ pkgs, lib, ... }:
 
 with lib;
 
@@ -43,4 +43,4 @@ in pkgs.writeText "answers" ''
 
   Task2:
     ${answer2}
-''
\ No newline at end of file
+''
diff --git a/day05/default.nix b/day05/default.nix
index 1b4fb47..d87d497 100644
--- a/day05/default.nix
+++ b/day05/default.nix
@@ -1,4 +1,4 @@
-{ pkgs, lib }:
+{ pkgs, lib, ... }:
 
 with lib;
 
diff --git a/day06/default.nix b/day06/default.nix
index 34b5729..2c3070e 100644
--- a/day06/default.nix
+++ b/day06/default.nix
@@ -1,8 +1,10 @@
-{ pkgs, lib }:
+{ pkgs, lib, AoCLib, ... }:
 
 with lib;
 
 let
+  inherit (AoCLib) allUnique;
+
   countWithNUntil = n: pred: list: let
     inner = list': count:
       if pred (take n list')
@@ -10,13 +12,10 @@ let
         else inner (tail list') (count + 1);
   in inner list 0;
 
-  allItemsAreUnique = l: l == []
-    || !(elem (head l) (tail l)) && allItemsAreUnique (tail l);
-
   answerN = n: pipe ./input.txt [
     fileContents
     stringToCharacters
-    (countWithNUntil n allItemsAreUnique)
+    (countWithNUntil n allUnique)
     (add n)
     toString
   ];
diff --git a/day07/default.nix b/day07/default.nix
index c248290..769a254 100644
--- a/day07/default.nix
+++ b/day07/default.nix
@@ -1,4 +1,4 @@
-{ pkgs, lib }:
+{ pkgs, lib, ... }:
 
 with lib;
 
diff --git a/day08/default.nix b/day08/default.nix
index 280713f..31e7f2e 100644
--- a/day08/default.nix
+++ b/day08/default.nix
@@ -1,8 +1,10 @@
-{ pkgs, lib }:
+{ pkgs, lib, AoCLib, ... }:
 
 with lib;
 
 let
+  inherit (AoCLib) transpose countWhile multiply;
+
   calculateTreeVisibilityForLine = line: let
     updateState = { currentMax ? (-1), trees ? [] }: tree:
       if tree > currentMax then { currentMax = tree; trees = trees ++ [true]; }
@@ -11,9 +13,6 @@ let
     backwards = reverseList (foldr (flip updateState) { } line).trees;
   in zipListsWith or forwards backwards;
 
-  transpose = grid: 
-    genList (n: map ((flip elemAt) n) grid) (length grid);
-
   combineGridsWith = f: grid1: grid2: let
     height = length grid1;
     width = length (elemAt grid1 0);
@@ -88,13 +87,13 @@ let
       visibleDistanceBackwards 
       reverseList
     ];
-  in zipListsWith (x: y: x * y) forwards backwards;
+  in zipListsWith multiply forwards backwards;
 
   answer2 = pipe trees [
     (lines: { horizontal = lines; vertical = transpose lines; })
     (mapAttrs (_: map visibleDistanceHorizontal))
     ({horizontal, vertical}: { inherit horizontal; vertical = transpose vertical; })
-    ({horizontal, vertical}: combineGridsWith (x: y: x * y) horizontal vertical)
+    ({horizontal, vertical}: combineGridsWith multiply horizontal vertical)
     (map (foldr max 0))
     (foldr max 0)
     toString
diff --git a/day09/default.nix b/day09/default.nix
index 69bc143..3e38cf3 100644
--- a/day09/default.nix
+++ b/day09/default.nix
@@ -1,8 +1,10 @@
-{ pkgs, lib }:
+{ pkgs, lib, AoCLib, ... }:
 
 with lib;
 
 let
+  inherit (AoCLib) scanl abs repeat cmp;
+
   mapDirectionStepsToHorizontalVertical = { direction, steps }: {
     horizontal = if direction == "L" then steps else
                  if direction == "R" then -steps else 0;
@@ -10,11 +12,6 @@ let
                if direction == "U" then -steps else 0;
   };
 
-  scanl = f: x1: list: let
-    x2 = head list;
-    x1' = f x1 x2;
-  in if list == [] then [] else [x1'] ++ (scanl f x1' (tail list));
-
   foldHeadPosition =
     { x ? 0, y ? 0 }: 
     { horizontal, vertical }: {
@@ -31,20 +28,14 @@ let
     (scanl foldHeadPosition {})
   ];
 
-  abs = x: if x < 0 then -x else x;
-
   ropePieceLength = headPiece: tailPiece: let
     deltaX = abs (headPiece.x - tailPiece.x);
     deltaY = abs (headPiece.y - tailPiece.y);
   in max deltaX deltaY;
 
   moveRopePiece = headPiece: tailPiece: {
-    x = if headPiece.x > tailPiece.x then tailPiece.x + 1 else
-        if headPiece.x < tailPiece.x then tailPiece.x - 1 else 
-                                          tailPiece.x;
-    y = if headPiece.y > tailPiece.y then tailPiece.y + 1 else
-        if headPiece.y < tailPiece.y then tailPiece.y - 1 else 
-                                          tailPiece.y;
+    x = tailPiece.x + (cmp headPiece.x tailPiece.x);
+    y = tailPiece.y + (cmp headPiece.y tailPiece.y);
   };
 
   moveRope = headToOverlap: rope: let
@@ -69,8 +60,6 @@ let
          tailPositions = [(last newRope)] ++ nextIteration.tailPositions;
         };
 
-  repeat = item: times: map (const item) (range 1 times);
-
   f = n: { rope ? (repeat { x = 0; y = 0; } n), tailPositions ? [{ x = 0; y = 0; }] }: newHeadPosition: let
     newRope = moveRopeUntilHeadOverlapsAndReportLastPositions newHeadPosition rope;
   in {
diff --git a/day10/default.nix b/day10/default.nix
index a3cf278..08e0ba7 100644
--- a/day10/default.nix
+++ b/day10/default.nix
@@ -1,39 +1,9 @@
-{ pkgs, lib }:
+{ pkgs, lib, AoCLib, ... }:
 
 with lib;
 
 let
-  # See https://github.com/NixOS/nixpkgs/pull/205457
-  toInt = str:
-    let
-      inherit (builtins) match fromJSON;
-      # RegEx: Match any leading whitespace, possibly a '-', one or more digits,
-      # and finally match any trailing whitespace.
-      strippedInput = match "[[:space:]]*(-?[[:digit:]]+)[[:space:]]*" str;
-
-      # RegEx: Match a leading '0' then one or more digits.
-      isLeadingZero = match "0[[:digit:]]+" (head strippedInput) == [];
-
-      # Attempt to parse input
-      parsedInput = fromJSON (head strippedInput);
-
-      generalError = "toInt: Could not convert ${escapeNixString str} to int.";
-
-      octalAmbigError = "toInt: Ambiguity in interpretation of ${escapeNixString str}"
-      + " between octal and zero padded integer.";
-
-    in
-      # Error on presence of non digit characters.
-      if strippedInput == null
-      then throw generalError
-      # Error on presence of leading zero/octal ambiguity.
-      else if isLeadingZero
-      then throw octalAmbigError
-      # Error if parse function fails.
-      else if !isInt parsedInput
-      then throw generalError
-      # Return result.
-      else parsedInput;
+  inherit (AoCLib) toInt repeat takeWithStride chunksOf;
 
   lineToInstruction = line:
     if line == "noop"
@@ -48,17 +18,12 @@ let
                         else { cycles = 2; X = nextX; nextX = nextX + instr.val; };
   in if instructions == [] then [] else [nextSignalState] ++ (foldToSignalState nextSignalState (tail instructions));
 
-  repeat = item: times: map (const item) (range 1 times);
-
   expandSignalStates = signalStates: let
     s = head signalStates;
   in if signalStates == []
        then []
        else (repeat s.X s.cycles) ++ (expandSignalStates (tail signalStates));
 
-  takeWithStride = n: l:
-    if l == [] then [] else [(head l)] ++ takeWithStride n (drop n l);
-
   signalStates = pipe ./input.txt [
     fileContents
     (splitString "\n")
@@ -75,14 +40,10 @@ let
     toString
   ];
 
-  splitAtInterval = n: list:
-    if list == [] then []
-                  else [(take n list)] ++ (splitAtInterval n (drop n list));
-
   f = i: v: if v <= i && i <= v + 2 then "#" else ".";
 
   answer2 = pipe signalStates [
-    (splitAtInterval 40)
+    (chunksOf 40)
     (map (imap1 f))
     (map (concatStringsSep ""))
     (concatStringsSep "\n")
diff --git a/flake.nix b/flake.nix
index c8c46d1..719a711 100644
--- a/flake.nix
+++ b/flake.nix
@@ -5,17 +5,18 @@
     system = "x86_64-linux";
     pkgs = nixpkgs.legacyPackages.${system};
   in {
+    AoCLib = pkgs.callPackage ./lib.nix { };
     packages.${system} = {
-      day01 = pkgs.callPackage ./day01 { };
-      day02 = pkgs.callPackage ./day02 { };
-      day03 = pkgs.callPackage ./day03 { };
-      day04 = pkgs.callPackage ./day04 { };
-      day05 = pkgs.callPackage ./day05 { };
-      day06 = pkgs.callPackage ./day06 { };
-      day07 = pkgs.callPackage ./day07 { };
-      day08 = pkgs.callPackage ./day08 { };
-      day09 = pkgs.callPackage ./day09 { };
-      day10 = pkgs.callPackage ./day10 { };
+      day01 = pkgs.callPackage ./day01 { inherit (self) AoCLib; };
+      day02 = pkgs.callPackage ./day02 { inherit (self) AoCLib; };
+      day03 = pkgs.callPackage ./day03 { inherit (self) AoCLib; };
+      day04 = pkgs.callPackage ./day04 { inherit (self) AoCLib; };
+      day05 = pkgs.callPackage ./day05 { inherit (self) AoCLib; };
+      day06 = pkgs.callPackage ./day06 { inherit (self) AoCLib; };
+      day07 = pkgs.callPackage ./day07 { inherit (self) AoCLib; };
+      day08 = pkgs.callPackage ./day08 { inherit (self) AoCLib; };
+      day09 = pkgs.callPackage ./day09 { inherit (self) AoCLib; };
+      day10 = pkgs.callPackage ./day10 { inherit (self) AoCLib; };
     };
   };
 }
diff --git a/lib.nix b/lib.nix
new file mode 100644
index 0000000..f4c0b4f
--- /dev/null
+++ b/lib.nix
@@ -0,0 +1,117 @@
+{ pkgs, lib }: with lib; rec {
+  # Transpose a square grid
+  #
+  # [[a]] -> [[a]]
+  transpose = grid: 
+    genList (n: map ((flip elemAt) n) grid) (length grid);
+
+  # Checks if there are any duplicate items in the list,
+  # in which case it returns false.
+  #
+  # [a] -> Bool
+  allUnique = list: list == []
+                 || !(elem (head list) (tail list)) && allUnique (tail list);
+
+  # Takes items until either a predicate fails, or the list is empty.
+  #
+  # (a -> Bool) -> [a] -> Int
+  takeWhile = pred: xs:
+    if xs == [] || !(stopPred (head xs))
+      then []
+      else [(head xs)] + (takeWhile pred (tail xs));
+
+  # Counts items until either a predicate fails, or the list is empty
+  #
+  # (a -> Bool) -> [a] -> Int
+  countWhile = pred: xs: length (takeWhile head xs);
+
+  # Like foldl, but keeps all intermediate values
+  #
+  # (b -> a -> b) -> b -> [a] -> [b]
+  scanl = f: x1: list: let
+    x2 = head list;
+    x1' = f x1 x2;
+  in if list == [] then [] else [x1'] ++ (scanl f x1' (tail list));
+
+  # Like scanl, but uses the first element as its start element.
+  #
+  # (a -> a -> a) -> [a] -> [a]
+  scanl1 = f: list: 
+    if list == [] then [] else scanl f (head list) (tail list);
+
+  # See https://github.com/NixOS/nixpkgs/pull/205457
+  toInt = str:
+    let
+      inherit (builtins) match fromJSON;
+      # RegEx: Match any leading whitespace, possibly a '-', one or more digits,
+      # and finally match any trailing whitespace.
+      strippedInput = match "[[:space:]]*(-?[[:digit:]]+)[[:space:]]*" str;
+
+      # RegEx: Match a leading '0' then one or more digits.
+      isLeadingZero = match "0[[:digit:]]+" (head strippedInput) == [];
+
+      # Attempt to parse input
+      parsedInput = fromJSON (head strippedInput);
+
+      generalError = "toInt: Could not convert ${escapeNixString str} to int.";
+
+      octalAmbigError = "toInt: Ambiguity in interpretation of ${escapeNixString str}"
+      + " between octal and zero padded integer.";
+
+    in
+      # Error on presence of non digit characters.
+      if strippedInput == null
+      then throw generalError
+      # Error on presence of leading zero/octal ambiguity.
+      else if isLeadingZero
+      then throw octalAmbigError
+      # Error if parse function fails.
+      else if !isInt parsedInput
+      then throw generalError
+      # Return result.
+      else parsedInput;
+
+  # Trivial function to wrap around the multiplication operation.
+  #
+  # Number -> Number -> Number
+  multiply = x: y: x * y;
+
+  # Trivial function to take the absolute value of a number
+  #
+  # Number -> Number
+  abs = x: if x < 0 then -x else x;
+
+  # Generate a list by repeating an element n times.
+  #
+  # a -> Int -> [a]
+  repeat = item: times: map (const item) (range 1 times);
+
+  # Compare two items, return either 1, 0, or -1 depending on whether
+  # one is bigger than the other.
+  #
+  # Ord a => a -> a -> Int
+  cmp = x: y: if x > y then 1 else if x < y then -1 else 0;
+
+  # Take 1 item, and skip the n-1 next items continuosly until the list is empty.
+  #
+  # Int -> [a] -> [a]
+  takeWithStride = n: l:
+    if l == [] then [] else [(head l)] ++ takeWithStride n (drop n l);
+
+  # Split a list at every n items.
+  #
+  # Int -> [a] -> [[a]]
+  chunksOf = n: list: if list == []
+                        then []
+                        else [(take n list)] ++ (chunksOf n (drop n list));
+
+  # Map something orderable through a function f if it is between min and max.
+  #
+  # Ord a => a -> a -> (a -> b) -> a -> Either a b
+  mapRange = min: max: f: o: if min <= o && o < max then f o else o;
+
+  # Shift a number n by an offset if it is between min and max.
+  #
+  # Number -> Number -> Number -> Number -> Number
+  transformRange = min: max: offset: n: mapRange min max (x: x + offset) n;
+}