diff --git a/examples/particles/Cargo.toml b/examples/particles/Cargo.toml
index 7c7caa8..ac474eb 100644
--- a/examples/particles/Cargo.toml
+++ b/examples/particles/Cargo.toml
@@ -6,4 +6,4 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-hypoloop = {version = "0.1.1", path = "D:/Code/hypoloop"}
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+hypoloop = {version = "0.1.1", path = "D:/OneDrive/Code/hypoloop"}
\ No newline at end of file
diff --git a/examples/particles/src/main.rs b/examples/particles/src/main.rs
index fad6ce3..08148eb 100644
--- a/examples/particles/src/main.rs
+++ b/examples/particles/src/main.rs
@@ -1,16 +1,20 @@
-use hypoloop::Simulation;
+use hypoloop::core::Loop;
 
 // look into using closures for this
 fn main() {
     // create sim and configure it
-    let mut sim = Simulation::new();
-    sim.set_update_function(test);
+    let mut sim = Loop::new();
     //sim.set_realtime(false);
 
-    // run sim
-    sim.run();
-}
+    // test variable
+    let mut x: f32 = 0.0;
 
-fn test() {
-    println!("Test");
+    // run the simulation using custom update logic
+    sim.run(|state| {
+        state.debug_tick();
+        
+        x += 2.0 * state.get_timescale();
+
+        //println!("Delta time: {} | Timescale: {} | Sim time: {} | x: {}", state.get_delta_time(), state.get_timescale(), state.get_sim_time().as_millis(), x);
+    });
 }
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diff --git a/src/lib.rs b/src/lib.rs
index 6faaa63..5bcb58f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,145 +1,177 @@
-use std::time::{Duration, Instant};
+pub mod core {
+    use std::time::{Duration, Instant};
+    
+    /// Contains mutable simulation state which can be changed via callback functions
+    #[derive(Copy, Clone)]
+    pub struct State {
+        update_interval: u32,
+        timescale: f32,
+        simulate: bool,
+        delta_time: u32,
+        irl_time: Duration,
+        sim_time: Duration,
+        last_tick: Instant
+    }
 
-// debug constants
-const DEBUG_LOOP: bool = false;
-const DEBUG_TIME: bool = true;
+    impl State {
+        /// Creates a default State object
+        pub fn new() -> State {
+            // Create default state object
+            let mut new_state = State {
+                update_interval: 40,
+                timescale: 1.0,
+                simulate: true,
+                delta_time: 0,
+                irl_time: Duration::new(0,0),
+                sim_time: Duration::new(0,0),
+                last_tick: Instant::now()
+            };
 
-/// Contains all per-simulation logic and state
-// update_interval is the minimum delay (in milliseconds) between update ticks
-// timescale is the rate of the simulation proportional to real-time
-// if realtime is false, the simulation runs as fast as possible and doesn't run the display function
-pub struct Simulation {
-    update_interval: u32,
-    timescale: f32,
-    realtime: bool,
-    simulate: bool,
-    update_function: fn(),
-    display_function: fn()
-}
+            // Make sure that delta_time always starts the same as update_interval
+            new_state.delta_time = new_state.update_interval;
 
-impl Simulation {
-    /// Creates a new simulation with default values
-    pub fn new() -> Simulation {
-        Simulation {
-            update_interval: 40,
-            timescale: 1.0,
-            realtime: true,
-            simulate: true,
-            update_function: default_update,
-            display_function: default_display
+            // Return this default state
+            new_state
+        }
+
+        /// Returns the current "delta time", the time elapsed since the last update tick in milliseconds
+        pub fn get_delta_time(self) -> u32 {
+            self.delta_time
+        }
+
+        /// Returns the current IRL time elapsed since the start of the simulation
+        pub fn get_irl_time(self) -> Duration {
+            self.irl_time
+        }
+
+        /// Returns the current simulation time elapsed since the start of the simulation
+        pub fn get_sim_time(self) -> Duration {
+            self.sim_time
+        }
+
+        /// Returns the current "timescale", the speed of simulation time relative to real time
+        pub fn get_timescale(self) -> f32 {
+            self.timescale
+        }
+
+        /// Returns the time of the last tick
+        pub fn get_last_tick(self) -> Instant {
+            self.last_tick
+        }
+
+        /// Pauses the simulation
+        pub fn pause(&mut self) {
+            self.simulate = false;
+        }
+
+        /// Resumes the simulation
+        pub fn resume(&mut self) {
+            self.simulate = true;
+        }
+
+        /// Changes the simulation timescale
+        pub fn set_timescale(&mut self, timescale: f32) {
+            self.timescale = timescale;
+        }
+
+        /// Prints a string of information about the current tick
+        pub fn debug_tick(self) {
+            let elapsed_time = Instant::now().duration_since(self.last_tick);
+            let loop_delay_ms = elapsed_time.as_nanos() as f32 / 1_000_000.0;
+            let loop_rate_hz = 1000.0 / loop_delay_ms;
+            println!("IRL time: {}ms | Sim time: {}ms | Tick delay/rate: {}ms/{}hz", self.irl_time.as_millis(), self.sim_time.as_millis(), loop_delay_ms, loop_rate_hz);
         }
     }
 
-    /// Allows the user to pass in a custom update function
-    pub fn set_update_function(&mut self, user_function: fn()) {
-        self.update_function = user_function;
+    /// The simulation loop itself
+    pub struct Loop {
+        state: State,
+        realtime: bool
     }
-
-    /// Allows the user to pass in a custom display function
-    pub fn set_display_function(&mut self, user_function: fn()) {
-        self.display_function = user_function;
-    }
-
-    /// Allows the user to turn realtime mode on/off
-    pub fn set_realtime(&mut self, realtime: bool) {
-        self.realtime = realtime;
-    }
-
-    /// Initializes and runs the simulation
-    pub fn run(&self) {
-        // start the clock to keep track of real time
-        let clock_start = Instant::now();
     
-        // keep track of the last tick time
-        let mut last_tick = Instant::now();
+    impl Loop {
+        /// Creates a new simulation with default values
+        pub fn new() -> Loop {
+            // Return a Loop object with a default State
+            Loop {
+                state: State::new(),
+                realtime: true
+            }
+        }
     
-        // real-time and sim-time clocks
-        let mut irl_time = Duration::new(0, 0);
-        let mut sim_time = Duration::new(0, 0);
-    
-        while self.simulate {
-            // TODO - support frameskips
-            if !self.realtime || delta_time(last_tick) >= self.update_interval {
-                // mutable delta time and timescale for flexibility
-                let mut current_timescale: f32;
-                let mut current_delta_time: u32;
-                let elapsed_time = Instant::now().duration_since(last_tick);
+        /// Initializes and runs the simulation using a user-supplied callback as the update logic
+        pub fn run(&mut self, mut update_callback: impl FnMut(&mut State)) {
+            // Make sure the simulation will run
+            self.state.simulate = true;
+
+            // start the clock to keep track of real time
+            let clock_start = Instant::now();
                 
-                // update clocks
+            while self.state.simulate {
+                // TODO - support frameskips
+                if !self.realtime || delta_time(self.state.last_tick) >= self.state.update_interval {
+                    // mutable delta time and timescale for flexibility
+                    let elapsed_time = Instant::now().duration_since(self.state.last_tick);
+                    
+                    // update clocks
+                    if self.realtime {
+                        self.state.delta_time = delta_time(self.state.last_tick);
+                        self.state.sim_time += elapsed_time.mul_f32(self.state.timescale);
+                        self.state.irl_time += elapsed_time;
+                    } else {
+                        self.state.delta_time = self.state.update_interval;
+                        self.state.sim_time += Duration::from_millis(self.state.update_interval as u64);
+                        self.state.irl_time = Instant::now().duration_since(clock_start);
+                    }
+        
+                    // update
+                    update_callback(&mut self.state);
+        
+                    // record last tick time
+                    self.state.last_tick = Instant::now();
+                }
+        
+                // display
                 if self.realtime {
-                    current_timescale = self.timescale;
-                    current_delta_time = delta_time(last_tick);
-                    sim_time += elapsed_time.mul_f32(self.timescale);
-                    irl_time += elapsed_time;
-                } else {
-                    current_timescale = 1.0;
-                    current_delta_time = self.update_interval;
-                    sim_time += Duration::from_millis(self.update_interval as u64);
-                    irl_time = Instant::now().duration_since(clock_start);
+                    display(delta_time(self.state.last_tick), self.state.timescale, self.state.update_interval);
                 }
-    
-                // DEBUG
-                if DEBUG_TIME {
-                    let loop_delay_ms = elapsed_time.as_nanos() as f32 / 1_000_000.0;
-                    let loop_rate_hz = 1000.0 / loop_delay_ms;
-                    println!("Realtime: {} | IRL time: {}ms | Sim time: {}ms | Tick delay/rate: {}ms/{}hz", self.realtime, irl_time.as_millis(), sim_time.as_millis(), loop_delay_ms, loop_rate_hz);
-                }
-    
-                // record last tick time
-                last_tick = Instant::now();
-    
-                // update
-                update(self.update_function, current_delta_time, current_timescale);
-            }
-    
-            // display
-            if self.realtime {
-                display(self.display_function, delta_time(last_tick), self.timescale, self.update_interval);
             }
         }
+
+        /// Turns real-time mode on/off
+        pub fn set_realtime(&mut self, realtime: bool) {
+            self.realtime = realtime;
+        }
     }
-}
-
-
-// update function
-// this is where all your per-tick logic should go
-fn update(user_function: fn(), delta_time: u32, timescale: f32) {
-    // DEBUG
-    if DEBUG_LOOP {
-        println!("Updating...");
+    
+    
+    // update function
+    // this is where all your per-tick logic should go
+    fn update(user_function: fn(), delta_time: u32, timescale: f32) {
+        // use timestep to scale per-tick calculations appropriately
+        let timestep: f32 = delta_time as f32 / 1000.0 * timescale;
+    
+        // call user update function
+        user_function();
     }
-
-    // use timestep to scale per-tick calculations appropriately
-    let timestep: f32 = delta_time as f32 / 1000.0 * timescale;
-
-    // call user update function
-    user_function();
-}
-
-// display function
-// this is where you should call a render function
-fn display(user_function: fn(), delta_time: u32, timescale: f32, update_interval: u32) {
-    // DEBUG
-    if DEBUG_LOOP {
-        println!("Displaying...");
+    
+    // display function
+    // this is where you should call a render function
+    fn display(delta_time: u32, timescale: f32, update_interval: u32) {
+        // use interpolation to smooth display values between ticks
+        let interpolation: f32 = delta_time as f32 / update_interval as f32 * timescale;
+    }
+    
+    // gets the time in milliseconds that's elapsed since the earlier Instant
+    fn delta_time(earlier: Instant) -> u32 {
+        Instant::now().duration_since(earlier).as_millis() as u32
+    }
+    
+    // default update function (does nothing)
+    fn default_update() {
+    }
+    
+    // default display function (does nothing)
+    fn default_display() {
     }
-
-    // use interpolation to smooth display values between ticks
-    let interpolation: f32 = delta_time as f32 / update_interval as f32 * timescale;
-
-    // call user display function
-    user_function();
-}
-
-// gets the time in milliseconds that's elapsed since the earlier Instant
-fn delta_time(earlier: Instant) -> u32 {
-    Instant::now().duration_since(earlier).as_millis() as u32
-}
-
-// default update function (does nothing)
-fn default_update() {
-}
-
-// default display function (does nothing)
-fn default_display() {
 }
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