diff --git a/day12.c3 b/day12.c3
index 2a5954f..03807a1 100644
--- a/day12.c3
+++ b/day12.c3
@@ -3,7 +3,7 @@ import std::io;
 import std::math;
 import std::collections::list;
 
-define MapList = List<String>;
+typedef MapList = List<String>;
 
 struct Map
 {
diff --git a/day13.c3 b/day13.c3
index db87874..f0a09c8 100644
--- a/day13.c3
+++ b/day13.c3
@@ -9,11 +9,11 @@ struct PacketPair
 	Packet* p2;
 }
 
-define PacketList = List<Packet*>;
+typedef PacketList = List<Packet*>;
 
-define Packet = List<PacketElement*>;
+typedef Packet = List<PacketElement*>;
 
-define PacketPairs = List<PacketPair>;
+typedef PacketPairs = List<PacketPair>;
 
 struct PacketElement
 {
diff --git a/day14.c3 b/day14.c3
index 447e9fc..66bf514 100644
--- a/day14.c3
+++ b/day14.c3
@@ -3,7 +3,7 @@ import std::io;
 import std::math;
 
 const ENV_SIDE = 1000;
-define Environment = int[ENV_SIDE][ENV_SIDE];
+typedef Environment = int[ENV_SIDE][ENV_SIDE];
 
 enum Result
 {
diff --git a/day15.c3 b/day15.c3
index fab9d56..810ca4e 100644
--- a/day15.c3
+++ b/day15.c3
@@ -4,7 +4,7 @@ import std::math;
 import std::collections::list;
 import std::collections::priorityqueue;
 
-define CoordPairList = List<int[<2>][2]>;
+typedef CoordPairList = List<int[<2>][2]>;
 
 fn int[<2>]! parse_coord(String s)
 {
diff --git a/day16.c3 b/day16.c3
index 3c4d07e..22d1698 100644
--- a/day16.c3
+++ b/day16.c3
@@ -4,8 +4,8 @@ import std::math;
 import std::collections::map;
 import std::collections::list;
 
-define ValveMap = HashMap<String, int>;
-define IntPairList = List<int[<2>]>;
+typedef ValveMap = HashMap<String, int>;
+typedef IntPairList = List<int[<2>]>;
 ValveMap v;
 
 struct Valve
diff --git a/day17.c3 b/day17.c3
index 150eb6d..71a389e 100644
--- a/day17.c3
+++ b/day17.c3
@@ -4,7 +4,7 @@ import std::math;
 import std::collections::map;
 import std::collections::list;
 
-define StateCacheMap = HashMap<StateCache, int>;
+typedef StateCacheMap = HashMap<StateCache, int>;
 
 struct StateCache
 {
@@ -85,7 +85,7 @@ Shape[5] shapes = {
 	}
 };
 
-define GameRow = distinct char;
+typedef GameRow = distinct char;
 GameRow[1000] game;
 
 macro bool GameRow.is_full(GameRow row)
diff --git a/day19.c3 b/day19.c3
index 8c00e75..bd70fd1 100644
--- a/day19.c3
+++ b/day19.c3
@@ -4,7 +4,7 @@ import std::math;
 import std::collections::map;
 import std::collections::list;
 
-define BlueprintList = List<Blueprint>;
+typedef BlueprintList = List<Blueprint>;
 
 const usz ORE = 0;
 const usz CLAY = 1;
diff --git a/day20.c3 b/day20.c3
index 8432b89..ff83a1a 100644
--- a/day20.c3
+++ b/day20.c3
@@ -4,7 +4,7 @@ import std::math;
 import std::collections::map;
 import std::collections::list;
 
-define LongList = List<long>;
+typedef LongList = List<long>;
 
 fn void load_crypto(LongList* list, LongList* pos, long key)
 {
diff --git a/day21.c3 b/day21.c3
index 389ea8b..0f11b21 100644
--- a/day21.c3
+++ b/day21.c3
@@ -4,8 +4,8 @@ import std::math;
 import std::collections::map;
 import std::collections::list;
 
-define MonkeyList = List<Monkey>;
-define NameMap = HashMap<String, MonkeyId>;
+typedef MonkeyList = List<Monkey>;
+typedef NameMap = HashMap<String, MonkeyId>;
 
 enum Action
 {
@@ -16,7 +16,7 @@ enum Action
 	MINUS,
 }
 
-define MonkeyId = distinct int;
+typedef MonkeyId = distinct int;
 
 struct Monkey
 {
diff --git a/day23.c3 b/day23.c3
index 3b21fea..5789678 100644
--- a/day23.c3
+++ b/day23.c3
@@ -3,7 +3,7 @@ import std::io;
 import std::math;
 import std::collections::list;
 
-define CharsArray = List<String>;
+typedef CharsArray = List<String>;
 
 // Pick a padding that doesn't hit the asserts.
 const int PADDING = 100;
diff --git a/day24.c3 b/day24.c3
index 8c1f1b5..e0dbf9d 100644
--- a/day24.c3
+++ b/day24.c3
@@ -3,7 +3,7 @@ import std::io;
 import std::math;
 import std::collections::list;
 
-define CharsArray = List<String>;
+typedef CharsArray = List<String>;
 
 const int PADDING = 100;
 
diff --git a/day3.c3 b/day3.c3
index 9c29c81..1139c0b 100644
--- a/day3.c3
+++ b/day3.c3
@@ -2,7 +2,7 @@ module day3;
 import std::io;
 import std::collections::map;
 
-define CharSet = HashMap<char, char>;
+typedef CharSet = HashMap<char, char>;
 
 fn int evaluate(char c)
 {
diff --git a/day5.c3 b/day5.c3
index 8a7ede0..e0b8ea7 100644
--- a/day5.c3
+++ b/day5.c3
@@ -2,7 +2,7 @@ module day5;
 import std::io;
 import std::collections::list;
 
-define CharList = list::List<char>;
+typedef CharList = list::List<char>;
 
 const MAX_PILES = 20;
 
diff --git a/day7.c3 b/day7.c3
index 8dd558b..17c5e96 100644
--- a/day7.c3
+++ b/day7.c3
@@ -2,7 +2,7 @@ module day7;
 import std::collections::list;
 import std::io;
 
-define DirList = List<Directory*>;
+typedef DirList = List<Directory*>;
 
 struct Directory
 {
diff --git a/day8.c3 b/day8.c3
index 8c4c0f7..77670bb 100644
--- a/day8.c3
+++ b/day8.c3
@@ -2,7 +2,7 @@ module day8;
 import std::collections::list;
 import std::io;
 
-define Forest = distinct List<String>;
+typedef Forest = distinct List<String>;
 fn Forest* parse_forest()
 {
 	File f = file::open("forest.txt", "rb")!!;