diff --git a/src/definitions.rs b/src/definitions.rs
index 701b7c8..487ffcd 100644
--- a/src/definitions.rs
+++ b/src/definitions.rs
@@ -1,6 +1,7 @@
+use parser::{SliceParseError, TagParseError};
 use serde::{Deserialize, Serialize};
 
-use self::parser::{FilePosition, ParseError, ParseQuery};
+use self::parser::{FilePosition, ParseError, SliceParse};
 
 pub mod parser;
 
@@ -18,8 +19,13 @@ pub struct Tag {
 }
 
 impl Tag {
-    fn parse_value<T: ParseQuery>(&self) -> Result<T, ParseError> {
-        T::parse(&self.values).map_err(|_| ParseError::ValueParseError(self.clone()))
+    fn parse_value<T: SliceParse>(&self) -> Result<T, ParseError> {
+        T::parse(&self.values).map_err(|err| {
+            ParseError::TagParseError(match err {
+                SliceParseError::ParseError => TagParseError::ParseError(self.clone()),
+                SliceParseError::MissingValue => TagParseError::MissingValue(self.clone()),
+            })
+        })
     }
 }
 
diff --git a/src/definitions/parser.rs b/src/definitions/parser.rs
index b18c3c2..1b86d4e 100644
--- a/src/definitions/parser.rs
+++ b/src/definitions/parser.rs
@@ -2,13 +2,13 @@ use std::{borrow::BorrowMut, io::Read, str::FromStr};
 
 use crate::definitions::{CreatureDef, SiteDef, Tag, TopLevelTag};
 
-pub trait ParseQuery: Sized {
-    fn parse(values: &Vec<String>) -> Result<Self, ()>;
+pub trait SliceParse: Sized {
+    fn parse(values: &[String]) -> Result<Self, SliceParseError>;
 }
 
 trait Parseable: Sized + FromStr {
-    fn parse(string: &str) -> Result<Self, ()> {
-        string.parse().map_err(|_| ())
+    fn parse(string: &str) -> Option<Self> {
+        string.parse().ok()
     }
 }
 
@@ -25,22 +25,20 @@ impl Parseable for bool {}
 
 macro_rules! parse_query_impl {
     ($t:ident) => {
-        impl<$t: Parseable> ParseQuery for $t {
-            fn parse(values: &Vec<String>) -> Result<Self, ()> {
+        impl<$t: Parseable> SliceParse for $t {
+            fn parse(values: &[String]) -> Result<Self, SliceParseError> {
                 let mut iter = values.iter();
-                Ok(
-                    $t::parse(iter.next().ok_or(())?)?
-                )
+                $t::parse(iter.next().ok_or(SliceParseError::MissingValue)?).ok_or(SliceParseError::ParseError)
             }
         }
     };
     ($x:ident, $($t:ident),+) => {
-        impl<$x: Parseable, $($t: Parseable),+> ParseQuery for ($x, $($t),+) {
-            fn parse(values: &Vec<String>) -> Result<Self, ()> {
+        impl<$x: Parseable, $($t: Parseable),+> SliceParse for ($x, $($t),+) {
+            fn parse(values: &[String]) -> Result<Self, SliceParseError> {
                 let mut iter = values.iter();
                 Ok((
-                    $x::parse(iter.next().ok_or(())?)?,
-                    $($t::parse(iter.next().ok_or(())?)?,)+
+                    $x::parse(iter.next().ok_or(SliceParseError::MissingValue)?).ok_or(SliceParseError::ParseError)?,
+                    $($t::parse(iter.next().ok_or(SliceParseError::MissingValue)?).ok_or(SliceParseError::ParseError)?,)+
                 ))
             }
         }
@@ -68,11 +66,22 @@ impl Default for FilePosition {
 pub enum ParseError {
     LexerError(LexerError),
     SyntaxError(String),
-    ValueParseError(Tag),
+    TagParseError(TagParseError),
     NoDefinitionsError,
     UnexpectedError,
 }
 
+pub enum SliceParseError {
+    MissingValue,
+    ParseError,
+}
+
+#[derive(Debug)]
+pub enum TagParseError {
+    MissingValue(Tag),
+    ParseError(Tag),
+}
+
 #[derive(Debug)]
 pub enum LexerError {
     Io(std::io::Error),
@@ -138,9 +147,7 @@ impl DefinitionParser {
         let mut tags = vec![];
         let mut tag_builder: Option<Tag> = None;
         let mut buffer = String::new();
-        source
-            .read_to_string(&mut buffer)
-            .map_err(|err| LexerError::Io(err))?;
+        source.read_to_string(&mut buffer).map_err(LexerError::Io)?;
         let mut file_position = FilePosition::default();
         for c in buffer.chars() {
             if c == '\n' {
diff --git a/src/main.rs b/src/main.rs
index 33c5563..4b02d42 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -6,38 +6,32 @@ use sim::{Site, World};
 pub mod definitions;
 pub mod sim;
 
-const SAVE_FILE: &'static str = "world.bin";
+const SAVE_FILE: &str = "world.bin";
 
 fn main() {
     let mut parse_error_files = vec![];
     let mut site_definitions = HashMap::new();
     let mut creature_definitions = HashMap::new();
-    for entry in std::fs::read_dir(resources_path()).unwrap() {
-        match entry {
-            Ok(entry) => {
-                if entry.file_name().to_string_lossy().ends_with(".def") {
-                    let source = BufReader::new(std::fs::File::open(entry.path()).unwrap());
-                    match DefinitionParser::parse(source) {
-                        Ok(defs) => {
-                            for def in defs.0 {
-                                if let Some(prev) = site_definitions.insert(def.id.clone(), def) {
-                                    eprintln!("Duplicate site definition '{}'", prev.id);
-                                }
-                            }
-                            for def in defs.1 {
-                                if let Some(prev) = creature_definitions.insert(def.id.clone(), def)
-                                {
-                                    eprintln!("Duplicate site definition '{}'", prev.id);
-                                }
-                            }
+    for entry in std::fs::read_dir(resources_path()).unwrap().flatten() {
+        if entry.file_name().to_string_lossy().ends_with(".def") {
+            let source = BufReader::new(std::fs::File::open(entry.path()).unwrap());
+            match DefinitionParser::parse(source) {
+                Ok(defs) => {
+                    for def in defs.0 {
+                        if let Some(prev) = site_definitions.insert(def.id.clone(), def) {
+                            eprintln!("Duplicate site definition '{}'", prev.id);
                         }
-                        Err(err) => {
-                            parse_error_files.push((err, entry.path()));
+                    }
+                    for def in defs.1 {
+                        if let Some(prev) = creature_definitions.insert(def.id.clone(), def) {
+                            eprintln!("Duplicate site definition '{}'", prev.id);
                         }
                     }
                 }
+                Err(err) => {
+                    parse_error_files.push((err, entry.path()));
+                }
             }
-            _ => (),
         }
     }
 
@@ -53,7 +47,7 @@ fn main() {
         Ok(data) => bincode::deserialize(&data).unwrap(),
         Err(_) => {
             let mut world = World::default();
-            let mut site = Site::from_def(&site_def);
+            let mut site = Site::from_def(site_def);
             site.populate_randomly(&creature_definitions.values().collect::<Vec<_>>());
             world.sites.push(site);
             std::fs::write("world.bin", bincode::serialize(&world).unwrap()).unwrap();
@@ -68,7 +62,7 @@ fn main() {
     let mut input = String::new();
     loop {
         std::io::stdin().read_line(&mut input).unwrap();
-        if vec!["q", "quit", "exit"]
+        if ["q", "quit", "exit"]
             .iter()
             .any(|quit_cmd| input.trim() == *quit_cmd)
         {
diff --git a/src/sim.rs b/src/sim.rs
index b2bf6f1..844262d 100644
--- a/src/sim.rs
+++ b/src/sim.rs
@@ -160,13 +160,13 @@ impl Display for Site {
             for creature in area.population.iter() {
                 write!(f, "\n\t\t{}", creature)?;
             }
-            if area.population.len() > 0 {
+            if !area.population.is_empty() {
                 write!(f, "\n\t")?;
             }
             write!(f, "]")?;
         }
         if !self.areas.is_empty() {
-            write!(f, "\n")?;
+            writeln!(f)?;
         }
         write!(f, "]")
     }
@@ -383,12 +383,12 @@ pub fn resolve_combat(combatants: &[Creature], max_rounds: u16) -> Option<Combat
             let c2 = &combatants[index_2];
             let is_enemy = c1.definition.id != c2.definition.id;
             if is_enemy {
-                if !participants.contains_key(&c1.uuid) {
-                    participants.insert(c1.uuid, CombatState::from_creature(c1.clone()));
-                }
-                if !participants.contains_key(&c2.uuid) {
-                    participants.insert(c2.uuid, CombatState::from_creature(c2.clone()));
-                }
+                participants
+                    .entry(c1.uuid)
+                    .or_insert(CombatState::from_creature(c1.clone()));
+                participants
+                    .entry(c2.uuid)
+                    .or_insert(CombatState::from_creature(c2.clone()));
                 participants
                     .get_mut(&c1.uuid)
                     .unwrap()
@@ -409,7 +409,7 @@ pub fn resolve_combat(combatants: &[Creature], max_rounds: u16) -> Option<Combat
     }
 
     // Time for violence
-    let mut order: Vec<Uuid> = participants.iter().map(|(uuid, _)| *uuid).collect();
+    let mut order: Vec<Uuid> = participants.keys().copied().collect();
     fastrand::shuffle(&mut order);
     let mut kills: Vec<_> = vec![];
     let mut attacks: Vec<_> = vec![];