diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..8af32f7
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,319 @@
+use kdl::KdlDocument;
+use serde_json::{from_str, Value};
+use std::collections::HashMap;
+use std::process::Command;
+use std::{fs, str};
+
+/// Configuration for swayout.
+struct Config {
+    /// Monitor name is independent of output name. It can be anything.
+    monitors: HashMap<String, Monitor>,
+    /// Definition of layouts: a map of the layout name to the outputs.
+    /// The outputs is a map of the monitor name (in `monitors`) to the configuration
+    /// of that monitor for this layout.
+    /// Available outputs that do not match a monitor in the map are disabled.
+    layouts: HashMap<String, HashMap<String, OutputConfig>>,
+}
+
+/// Defines a monitor by make, model, and serial.
+struct Monitor {
+    make: String,
+    model: String,
+    serial: String,
+}
+
+/// Configuration for an enabled output.
+struct OutputConfig {
+    /// mode. See man 5 sway-output
+    mode: String,
+    /// scale. See man 5 sway-output
+    scale: String,
+    /// x value for position. See man 5 sway-output
+    x: u16,
+    /// y value for position. See man 5 sway-output
+    y: u16,
+    /// transform. See man 5 sway-output
+    transform: String,
+}
+
+/// An output, as returned by `swaymsg -t get_outputs`.
+struct Output {
+    /// output name, according to sway
+    name: String,
+    make: String,
+    model: String,
+    serial: String,
+    output_config: OutputConfig,
+}
+
+/// Get all outputs currently available, according to `swaymsg -t get_outputs`.
+fn get_outputs() -> Vec<Output> {
+    let output = Command::new("swaymsg")
+        .arg("-t")
+        .arg("get_outputs")
+        .output()
+        .expect("swaymsg -t get_outputs failed");
+    let json_string = str::from_utf8(&output.stdout).unwrap();
+    let json = from_str(json_string).unwrap();
+
+    if let Value::Array(outputs) = json {
+        outputs
+            .iter()
+            .map(|output_json| Output {
+                name: String::from(output_json["name"].as_str().unwrap()),
+                make: String::from(output_json["make"].as_str().unwrap()),
+                model: String::from(output_json["model"].as_str().unwrap()),
+                serial: String::from(output_json["serial"].as_str().unwrap()),
+                output_config: OutputConfig {
+                    mode: get_mode(output_json),
+                    scale: String::from("1.0"),
+                    x: 0,
+                    y: 0,
+                    transform: String::from("normal"),
+                },
+            })
+            .collect()
+    } else {
+        panic!("outputs json was not an array");
+    }
+}
+
+/// Parse the mode from the output JSON into a string suitable for the mode param for sway-output.
+/// This will go into `OutputConfig.mode`.
+fn get_mode(output: &Value) -> String {
+    if let Value::Array(modes) = &output["modes"] {
+        if let Some(mode) = modes.first() {
+            let width = mode["width"].as_i64().unwrap().to_string();
+            let height = mode["height"].as_i64().unwrap().to_string();
+            let mut out: String = String::new();
+            out.push_str(&width);
+            out.push_str("x");
+            out.push_str(&height);
+            out
+        } else {
+            panic!("no modes")
+        }
+    } else {
+        panic!("modes not an array")
+    }
+}
+
+/// Get a `Config` from ~/.config/swayout/config.kdl.
+/// (It really uses XDG config dirs.)
+fn get_config() -> Config {
+    let xdg_dirs = xdg::BaseDirectories::with_prefix("swayout").unwrap();
+    if let Some(path) = xdg_dirs.find_config_file("config.kdl") {
+        let kdl = fs::read_to_string(path).expect("error reading file");
+        parse_config(kdl)
+    } else {
+        // no config files, use an empty rules
+        Config {
+            monitors: HashMap::new(),
+            layouts: HashMap::new(),
+        }
+    }
+}
+fn parse_config(kdl:String) -> Config {
+    let doc:KdlDocument = kdl.parse().expect("failed to parse config KDL");
+
+    let monitors:HashMap<String,Monitor> = doc.nodes().iter()
+        .filter(|node| node.name().value() == "monitor")
+        .map(|monitor_node| {
+            let name = String::from(monitor_node[0].as_string().unwrap());
+            let monitor = Monitor {
+                make : String::from(monitor_node["make"].as_string().unwrap()),
+                model : String::from(monitor_node["model"].as_string().unwrap()),
+                serial : String::from(monitor_node["serial"].as_string().unwrap()),
+            };
+            (name, monitor)
+        })
+        .collect();
+
+    let layouts:HashMap<String,HashMap<String,OutputConfig>> = doc.nodes().iter()
+        .filter(|node| node.name().value() == "layout")
+        .map(|layout_node| {
+            let layout_name = String::from(layout_node[0].as_string().unwrap());
+            let monitor_name_to_output_config:HashMap<String,OutputConfig> = layout_node
+                .children().unwrap().nodes().iter()
+                .map(|output_node| {
+                    let output = String::from(output_node[0].as_string().unwrap());
+                    let output_config = OutputConfig {
+                        mode : String::from(output_node["mode"].as_string().unwrap()),
+                        scale : String::from(output_node["scale"].as_string().unwrap()),
+                        transform : String::from(output_node["transform"].as_string().unwrap()),
+                        x : output_node["x"].as_i64().unwrap() as u16,
+                        y : output_node["y"].as_i64().unwrap() as u16,
+                    };
+                    (output, output_config)
+                })
+                .collect();
+            (layout_name,monitor_name_to_output_config)
+        })
+        .collect();
+
+    Config { monitors, layouts }
+}
+
+/// Determine the available layout names.
+/// Return one layout for each layout defined in the configuration file
+/// for which all outputs are available,
+/// one for each monitor defined in the configuration file (for using just that monitor),
+/// and one for each available output that is not a configured monitor (for using just that output).
+fn get_layouts() -> Vec<String> {
+    let available_outputs = get_outputs();
+    let config = get_config();
+
+    // Get the names of monitors that are available (that match an available output)
+    let available_monitor_names:Vec<&String> = config.monitors.iter()
+        .filter(|(_monitor_name,monitor)|
+            available_outputs.iter().any(|output|
+                monitor.make == output.make
+                    && monitor.model == output.model
+                    && output.serial == monitor.serial
+            )
+        )
+        .map(|(monitor_name,_monitor)| monitor_name)
+        .collect();
+
+    let mut layout_names: Vec<String> = Vec::new();
+
+    // Add each layout defined in the config file for which all outputs are available
+    config.layouts.iter().for_each(|(layout_name, layout)| {
+        if layout
+            .iter()
+            .all(|(output_name, _output)| available_monitor_names.contains(&output_name))
+        {
+            layout_names.push(String::from(layout_name))
+        }
+    });
+
+    // add each individual output (by monitor name if the monitor is defined, else by output name)
+    available_outputs.iter().for_each(|output| {
+        // if there is a monitor for the output, use the monitor name, else use the output name
+        let monitor_opt = config.monitors.iter()
+            .find(|(_monitor_name, monitor)| {
+                monitor.make == output.make
+                    && monitor.model == output.model
+                    && monitor.serial == output.serial
+            });
+        if let Some((monitor_name, _monitor)) = monitor_opt {
+            layout_names.push(String::from(monitor_name));
+        } else {
+            layout_names.push(String::from(&output.name));
+        }
+    });
+
+    layout_names
+}
+
+/// Print the name of each layout to standard out, one per line
+pub fn print_layout_names() {
+    get_layouts().iter().for_each(|layout| println!("{layout}"))
+}
+
+/// Apply the specified layout.
+/// layout_name may be the name of a layout in the config, the name of a monitor,
+/// or the name of an output.
+pub fn apply_layout(layout_name: &String) {
+    let rules = get_config();
+    let outputs = get_outputs();
+
+    // Map of output name to config for all outputs to enable.
+    // (All outputs not in this map will be disabled.)
+    let mut output_config_map: HashMap<&String, &OutputConfig> = HashMap::new();
+
+    // First check if the layout is defined in the rules
+    let opt_layout = rules.layouts.get(layout_name);
+    if let Some(layout) = opt_layout {
+        // The layout is defined in the rules.
+        layout.iter().for_each(|(monitor_name, output_config)| {
+            let monitor = &rules.monitors[monitor_name];
+
+            // find the output for the monitor to get the output name.
+            let output_opt = outputs.iter().find(|output| {
+                output.make == monitor.make
+                    && output.model == monitor.model
+                    && output.serial == monitor.serial
+            });
+            if let Some(output) = output_opt {
+                output_config_map.insert(&output.name, &output_config);
+            } else {
+                panic!("Missing output for monitor {monitor_name}");
+            }
+        });
+    } else {
+        // The layout is not defined in the rules.
+        // See if it is a monitor name...
+        if let Some(monitor) = rules.monitors.get(layout_name) {
+            // It is a monitor name. Find the matching output...
+            if let Some(output) = outputs.iter().find(|output| {
+                output.make == monitor.make && output.model == monitor.model
+                    && output.serial == monitor.serial
+            }) {
+                output_config_map.insert(&output.name, &output.output_config);
+            } else {
+                panic!("could not find output for monitor {layout_name}")
+            }
+        } else {
+            // See if it is an output name...
+            if let Some(output) = outputs.iter()
+                .find(|output| &output.name == layout_name) {
+                output_config_map.insert(&output.name, &output.output_config);
+            } else {
+                panic!("could not find layout, monitor, or output {layout_name}")
+            }
+        }
+    }
+
+    apply_outputs(&outputs, &output_config_map);
+}
+
+/// Apply the specified outputs. Enable all outputs in [outputs], disable others.
+fn apply_outputs(all_outputs: &Vec<Output>, outputs: &HashMap<&String, &OutputConfig>) {
+
+    // set enabled outputs first, then set disabled outputs.
+    // That way if some work before an error, you have at least one output enabled.
+
+    // for outputs to be enabled: map of output name to config
+    let mut enabled: HashMap<&String,&OutputConfig> = HashMap::new();
+    // for outputs to be disabled: output names
+    let mut disabled: Vec<&String> = Vec::new();
+
+    all_outputs.iter().for_each(|output| {
+        if let Some(output_config) = outputs.get(&output.name) {
+            enabled.insert(&output.name, &output_config);
+        } else {
+            disabled.push(&output.name);
+        }
+    });
+
+    let mut cmd = Command::new("swaymsg");
+    enabled.iter().for_each(|(output_name,output_config)| {
+        cmd.arg("output");
+        cmd.arg(&output_name);
+        cmd.arg("enable");
+        cmd.arg("mode");
+        cmd.arg(&output_config.mode);
+        cmd.arg("scale");
+        cmd.arg(&output_config.scale);
+        cmd.arg("pos");
+        cmd.arg(&output_config.x.to_string());
+        cmd.arg(&output_config.y.to_string());
+        cmd.arg("transform");
+        cmd.arg(&output_config.transform);
+        cmd.arg(",");
+    });
+
+    disabled.iter().for_each(|output_name| {
+        cmd.arg("output");
+        cmd.arg(&output_name);
+        cmd.arg("disable");
+        cmd.arg(",");
+    });
+
+    // print what we are about to do.
+    cmd.get_args()
+        .for_each(|arg| print!("{} ", arg.to_str().unwrap()));
+
+    cmd.output().expect("swaymsg output failed");
+}
\ No newline at end of file
diff --git a/src/main.rs b/src/main.rs
index 35db049..0e97482 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,332 +1,13 @@
-use kdl::KdlDocument;
-use serde_json::{from_str, Value};
-use std::collections::HashMap;
 use std::env;
-use std::process::Command;
-use std::{fs, str};
-
-/// Configuration for swayout.
-struct Config {
-    /// Monitor name is independent of output name. It can be anything.
-    monitors: HashMap<String, Monitor>,
-    /// Definition of layouts: a map of the layout name to the outputs.
-    /// The outputs is a map of the monitor name (in `monitors`) to the configuration
-    /// of that monitor for this layout.
-    /// Available outputs that do not match a monitor in the map are disabled.
-    layouts: HashMap<String, HashMap<String, OutputConfig>>,
-}
-
-/// Defines a monitor by make, model, and serial.
-struct Monitor {
-    make: String,
-    model: String,
-    serial: String,
-}
-
-/// Configuration for an enabled output.
-struct OutputConfig {
-    /// mode. See man 5 sway-output
-    mode: String,
-    /// scale. See man 5 sway-output
-    scale: String,
-    /// x value for position. See man 5 sway-output
-    x: u16,
-    /// y value for position. See man 5 sway-output
-    y: u16,
-    /// transform. See man 5 sway-output
-    transform: String,
-}
-
-/// An output, as returned by `swaymsg -t get_outputs`.
-struct Output {
-    /// output name, according to sway
-    name: String,
-    make: String,
-    model: String,
-    serial: String,
-    output_config: OutputConfig,
-}
 
 fn main() {
     let args: Vec<String> = env::args().collect();
     if args.len() == 1 {
         // first arg is executable
-        print_layout_names();
+        swayout::print_layout_names();
     } else if args.len() == 2 {
-        apply_layout(&args[1]);
+        swayout::apply_layout(&args[1]);
     } else {
         panic!("Usage: {} [layout]", args[0].as_str());
     }
-}
-
-/// Get all outputs currently available, according to `swaymsg -t get_outputs`.
-fn get_outputs() -> Vec<Output> {
-    let output = Command::new("swaymsg")
-        .arg("-t")
-        .arg("get_outputs")
-        .output()
-        .expect("swaymsg -t get_outputs failed");
-    let json_string = str::from_utf8(&output.stdout).unwrap();
-    let json = from_str(json_string).unwrap();
-
-    if let Value::Array(outputs) = json {
-        outputs
-            .iter()
-            .map(|output_json| Output {
-                name: String::from(output_json["name"].as_str().unwrap()),
-                make: String::from(output_json["make"].as_str().unwrap()),
-                model: String::from(output_json["model"].as_str().unwrap()),
-                serial: String::from(output_json["serial"].as_str().unwrap()),
-                output_config: OutputConfig {
-                    mode: get_mode(output_json),
-                    scale: String::from("1.0"),
-                    x: 0,
-                    y: 0,
-                    transform: String::from("normal"),
-                },
-            })
-            .collect()
-    } else {
-        panic!("outputs json was not an array");
-    }
-}
-
-/// Parse the mode from the output JSON into a string suitable for the mode param for sway-output.
-/// This will go into `OutputConfig.mode`.
-fn get_mode(output: &Value) -> String {
-    if let Value::Array(modes) = &output["modes"] {
-        if let Some(mode) = modes.first() {
-            let width = mode["width"].as_i64().unwrap().to_string();
-            let height = mode["height"].as_i64().unwrap().to_string();
-            let mut out: String = String::new();
-            out.push_str(&width);
-            out.push_str("x");
-            out.push_str(&height);
-            out
-        } else {
-            panic!("no modes")
-        }
-    } else {
-        panic!("modes not an array")
-    }
-}
-
-/// Get a `Config` from ~/.config/swayout/config.kdl.
-/// (It really uses XDG config dirs.)
-fn get_config() -> Config {
-    let xdg_dirs = xdg::BaseDirectories::with_prefix("swayout").unwrap();
-    if let Some(path) = xdg_dirs.find_config_file("config.kdl") {
-        let kdl = fs::read_to_string(path).expect("error reading file");
-        parse_config(kdl)
-    } else {
-        // no config files, use an empty rules
-        Config {
-            monitors: HashMap::new(),
-            layouts: HashMap::new(),
-        }
-    }
-}
-fn parse_config(kdl:String) -> Config {
-    let doc:KdlDocument = kdl.parse().expect("failed to parse config KDL");
-
-    let monitors:HashMap<String,Monitor> = doc.nodes().iter()
-        .filter(|node| node.name().value() == "monitor")
-        .map(|monitor_node| {
-            let name = String::from(monitor_node[0].as_string().unwrap());
-            let monitor = Monitor {
-                make : String::from(monitor_node["make"].as_string().unwrap()),
-                model : String::from(monitor_node["model"].as_string().unwrap()),
-                serial : String::from(monitor_node["serial"].as_string().unwrap()),
-            };
-            (name, monitor)
-        })
-        .collect();
-
-    let layouts:HashMap<String,HashMap<String,OutputConfig>> = doc.nodes().iter()
-        .filter(|node| node.name().value() == "layout")
-        .map(|layout_node| {
-            let layout_name = String::from(layout_node[0].as_string().unwrap());
-            let monitor_name_to_output_config:HashMap<String,OutputConfig> = layout_node
-                .children().unwrap().nodes().iter()
-                .map(|output_node| {
-                    let output = String::from(output_node[0].as_string().unwrap());
-                    let output_config = OutputConfig {
-                        mode : String::from(output_node["mode"].as_string().unwrap()),
-                        scale : String::from(output_node["scale"].as_string().unwrap()),
-                        transform : String::from(output_node["transform"].as_string().unwrap()),
-                        x : output_node["x"].as_i64().unwrap() as u16,
-                        y : output_node["y"].as_i64().unwrap() as u16,
-                    };
-                    (output, output_config)
-                })
-                .collect();
-            (layout_name,monitor_name_to_output_config)
-        })
-        .collect();
-
-    Config { monitors, layouts }
-}
-
-/// Determine the available layout names.
-/// Return one layout for each layout defined in the configuration file
-/// for which all outputs are available,
-/// one for each monitor defined in the configuration file (for using just that monitor),
-/// and one for each available output that is not a configured monitor (for using just that output).
-fn get_layouts() -> Vec<String> {
-    let available_outputs = get_outputs();
-    let config = get_config();
-
-    // Get the names of monitors that are available (that match an available output)
-    let available_monitor_names:Vec<&String> = config.monitors.iter()
-        .filter(|(_monitor_name,monitor)|
-            available_outputs.iter().any(|output|
-                monitor.make == output.make
-                    && monitor.model == output.model
-                    && output.serial == monitor.serial
-            )
-        )
-        .map(|(monitor_name,_monitor)| monitor_name)
-        .collect();
-
-    let mut layout_names: Vec<String> = Vec::new();
-
-    // Add each layout defined in the config file for which all outputs are available
-    config.layouts.iter().for_each(|(layout_name, layout)| {
-        if layout
-            .iter()
-            .all(|(output_name, _output)| available_monitor_names.contains(&output_name))
-        {
-            layout_names.push(String::from(layout_name))
-        }
-    });
-
-    // add each individual output (by monitor name if the monitor is defined, else by output name)
-    available_outputs.iter().for_each(|output| {
-        // if there is a monitor for the output, use the monitor name, else use the output name
-        let monitor_opt = config.monitors.iter()
-            .find(|(_monitor_name, monitor)| {
-                monitor.make == output.make
-                    && monitor.model == output.model
-                    && monitor.serial == output.serial
-            });
-        if let Some((monitor_name, _monitor)) = monitor_opt {
-            layout_names.push(String::from(monitor_name));
-        } else {
-            layout_names.push(String::from(&output.name));
-        }
-    });
-
-    layout_names
-}
-
-/// Print the name of each layout to standard out, one per line
-fn print_layout_names() {
-    get_layouts().iter().for_each(|layout| println!("{layout}"))
-}
-
-/// Apply the specified layout.
-/// layout_name may be the name of a layout in the config, the name of a monitor,
-/// or the name of an output.
-fn apply_layout(layout_name: &String) {
-    let rules = get_config();
-    let outputs = get_outputs();
-
-    // Map of output name to config for all outputs to enable.
-    // (All outputs not in this map will be disabled.)
-    let mut output_config_map: HashMap<&String, &OutputConfig> = HashMap::new();
-
-    // First check if the layout is defined in the rules
-    let opt_layout = rules.layouts.get(layout_name);
-    if let Some(layout) = opt_layout {
-        // The layout is defined in the rules.
-        layout.iter().for_each(|(monitor_name, output_config)| {
-            let monitor = &rules.monitors[monitor_name];
-
-            // find the output for the monitor to get the output name.
-            let output_opt = outputs.iter().find(|output| {
-                output.make == monitor.make
-                    && output.model == monitor.model
-                    && output.serial == monitor.serial
-            });
-            if let Some(output) = output_opt {
-                output_config_map.insert(&output.name, &output_config);
-            } else {
-                panic!("Missing output for monitor {monitor_name}");
-            }
-        });
-    } else {
-        // The layout is not defined in the rules.
-        // See if it is a monitor name...
-        if let Some(monitor) = rules.monitors.get(layout_name) {
-            // It is a monitor name. Find the matching output...
-            if let Some(output) = outputs.iter().find(|output| {
-                output.make == monitor.make && output.model == monitor.model
-                    && output.serial == monitor.serial
-            }) {
-                output_config_map.insert(&output.name, &output.output_config);
-            } else {
-                panic!("could not find output for monitor {layout_name}")
-            }
-        } else {
-            // See if it is an output name...
-            if let Some(output) = outputs.iter()
-                .find(|output| &output.name == layout_name) {
-                output_config_map.insert(&output.name, &output.output_config);
-            } else {
-                panic!("could not find layout, monitor, or output {layout_name}")
-            }
-        }
-    }
-
-    apply_outputs(&outputs, &output_config_map);
-}
-
-/// Apply the specified outputs. Enable all outputs in [outputs], disable others.
-fn apply_outputs(all_outputs: &Vec<Output>, outputs: &HashMap<&String, &OutputConfig>) {
-
-    // set enabled outputs first, then set disabled outputs.
-    // That way if some work before an error, you have at least one output enabled.
-
-    // for outputs to be enabled: map of output name to config
-    let mut enabled: HashMap<&String,&OutputConfig> = HashMap::new();
-    // for outputs to be disabled: output names
-    let mut disabled: Vec<&String> = Vec::new();
-
-    all_outputs.iter().for_each(|output| {
-        if let Some(output_config) = outputs.get(&output.name) {
-            enabled.insert(&output.name, &output_config);
-        } else {
-            disabled.push(&output.name);
-        }
-    });
-
-    let mut cmd = Command::new("swaymsg");
-    enabled.iter().for_each(|(output_name,output_config)| {
-        cmd.arg("output");
-        cmd.arg(&output_name);
-        cmd.arg("enable");
-        cmd.arg("mode");
-        cmd.arg(&output_config.mode);
-        cmd.arg("scale");
-        cmd.arg(&output_config.scale);
-        cmd.arg("pos");
-        cmd.arg(&output_config.x.to_string());
-        cmd.arg(&output_config.y.to_string());
-        cmd.arg("transform");
-        cmd.arg(&output_config.transform);
-        cmd.arg(",");
-    });
-
-    disabled.iter().for_each(|output_name| {
-        cmd.arg("output");
-        cmd.arg(&output_name);
-        cmd.arg("disable");
-        cmd.arg(",");
-    });
-
-    // print what we are about to do.
-    cmd.get_args()
-        .for_each(|arg| print!("{} ", arg.to_str().unwrap()));
-
-    cmd.output().expect("swaymsg output failed");
 }
\ No newline at end of file