diff --git a/dmc-lib/src/diagnostic.rs b/dmc-lib/src/diagnostic.rs
index 4044c2f..5fc8c08 100644
--- a/dmc-lib/src/diagnostic.rs
+++ b/dmc-lib/src/diagnostic.rs
@@ -1,3 +1,5 @@
+pub type Diagnostics = Vec<Diagnostic>;
+
 #[derive(Debug)]
 pub struct Diagnostic {
     message: String,
diff --git a/dmc-lib/src/error_codes.rs b/dmc-lib/src/error_codes.rs
index 32b3115..8f1a701 100644
--- a/dmc-lib/src/error_codes.rs
+++ b/dmc-lib/src/error_codes.rs
@@ -1,5 +1,7 @@
 pub type ErrorCode = usize;
 
+pub const LEXER_ERROR: ErrorCode = 1;
+pub const PARSE_ERROR: ErrorCode = 2;
 pub const SYMBOL_NOT_FOUND: ErrorCode = 13;
 pub const SYMBOL_ALREADY_DECLARED: ErrorCode = 14;
 pub const BINARY_INCOMPATIBLE_TYPES: ErrorCode = 15;
diff --git a/dmc-lib/src/lexer.rs b/dmc-lib/src/lexer.rs
index 4ad720e..5319373 100644
--- a/dmc-lib/src/lexer.rs
+++ b/dmc-lib/src/lexer.rs
@@ -118,7 +118,11 @@ impl<'a> Lexer<'a> {
                         }
                     }
                     if !terminated {
-                        return Some(Err(LexerError::new(LexerErrorKind::UnterminatedString)));
+                        return Some(Err(LexerError::new(
+                            self.position,
+                            end,
+                            LexerErrorKind::UnterminatedString,
+                        )));
                     }
                     (end, TokenKind::String)
                 } else {
@@ -133,9 +137,11 @@ impl<'a> Lexer<'a> {
                     }
 
                     if prefix.len() == 0 {
-                        return Some(Err(LexerError::new(LexerErrorKind::UnrecognizedCharacter(
-                            chunk.chars().next().unwrap(),
-                        ))));
+                        return Some(Err(LexerError::new(
+                            self.position,
+                            self.position + 1,
+                            LexerErrorKind::UnrecognizedCharacter(chunk.chars().next().unwrap()),
+                        )));
                     }
 
                     let token_kind = match prefix.as_str() {
@@ -162,12 +168,22 @@ impl<'a> Lexer<'a> {
 
 #[derive(Debug, Eq, PartialEq)]
 pub struct LexerError {
+    start: usize,
+    end: usize,
     kind: LexerErrorKind,
 }
 
 impl LexerError {
-    pub fn new(kind: LexerErrorKind) -> Self {
-        Self { kind }
+    pub fn new(start: usize, end: usize, kind: LexerErrorKind) -> Self {
+        Self { start, end, kind }
+    }
+
+    pub fn start(&self) -> usize {
+        self.start
+    }
+
+    pub fn end(&self) -> usize {
+        self.end
     }
 
     pub fn kind(&self) -> LexerErrorKind {
diff --git a/dmc-lib/src/parser.rs b/dmc-lib/src/parser.rs
index a7d0ebd..790cfba 100644
--- a/dmc-lib/src/parser.rs
+++ b/dmc-lib/src/parser.rs
@@ -19,20 +19,25 @@ use crate::ast::parameter::Parameter;
 use crate::ast::statement::Statement;
 use crate::ast::string_literal::StringLiteral;
 use crate::ast::type_use::TypeUse;
-use crate::diagnostic::Diagnostic;
-use crate::lexer::Lexer;
+use crate::diagnostic::{Diagnostic, Diagnostics};
+use crate::error_codes::{LEXER_ERROR, PARSE_ERROR};
+use crate::lexer::{Lexer, LexerErrorKind};
 use crate::source_range::SourceRange;
 use crate::token::{Token, TokenKind};
+use crate::{handle_diagnostics, ok_or_err_diagnostics};
 use std::str::FromStr;
 
-pub fn parse_compilation_unit(input: &str) -> Result<CompilationUnit, Vec<Diagnostic>> {
+pub type ParseResult<T> = Result<T, Diagnostics>;
+
+pub fn parse_compilation_unit(input: &str) -> ParseResult<CompilationUnit> {
     let mut parser = Parser::new(input);
+    parser.advance()?; // get started
     parser.compilation_unit()
 }
 
-pub fn parse_expression(input: &str) -> Result<Expression, Vec<Diagnostic>> {
+pub fn parse_expression(input: &str) -> ParseResult<Expression> {
     let mut parser = Parser::new(input);
-    parser.advance(); // get started
+    parser.advance()?; // get started
     parser.expression()
 }
 
@@ -96,96 +101,116 @@ impl<'a> Parser<'a> {
         }
     }
 
-    fn advance(&mut self) {
+    fn advance(&mut self) -> Result<(), Diagnostics> {
+        fn fetch(lexer: &mut Lexer) -> Result<Option<Token>, Diagnostics> {
+            let mut diagnostics = vec![];
+            let mut maybe_token: Option<Token> = None;
+            while let Some(lexer_result) = lexer.next() {
+                match lexer_result {
+                    Ok(token) => {
+                        maybe_token = Some(token);
+                        break;
+                    }
+                    Err(lexer_error) => {
+                        let diagnostic = match lexer_error.kind() {
+                            LexerErrorKind::UnterminatedString => Diagnostic::new(
+                                "Unterminated string literal.",
+                                lexer_error.start(),
+                                lexer_error.end(),
+                            )
+                            .with_error_code(LEXER_ERROR),
+                            LexerErrorKind::UnrecognizedCharacter(c) => Diagnostic::new(
+                                &format!("Unrecognized character: {}", c),
+                                lexer_error.start(),
+                                lexer_error.end(),
+                            )
+                            .with_error_code(LEXER_ERROR),
+                        };
+                        diagnostics.push(diagnostic);
+                    }
+                }
+            }
+            ok_or_err_diagnostics!(maybe_token, diagnostics)
+        }
+
         if self.lookahead.is_some() {
             // we've advanced at least once
             self.current = self.lookahead.take();
-            self.lookahead = match self.lexer.next() {
-                None => None,
-                Some(result) => match result {
-                    Ok(token) => Some(token),
-                    Err(lexer_error) => {
-                        panic!("{:?}", lexer_error);
-                    }
-                },
-            }
+            self.lookahead = fetch(&mut self.lexer)?;
+            Ok(())
         } else if self.lookahead.is_none() && self.current.is_some() {
             // we're on the last token
             self.current = None;
+            Ok(())
         } else {
             // we've not yet advanced, so fetch both
-            // current
-            match self.lexer.next() {
-                None => {}
-                Some(result) => match result {
-                    Ok(token) => {
-                        self.current = Some(token);
-                    }
-                    Err(lexer_error) => {
-                        panic!("{:?}", lexer_error);
-                    }
-                },
-            }
-            // lookahead
-            match self.lexer.next() {
-                None => {}
-                Some(result) => match result {
-                    Ok(token) => {
-                        self.lookahead = Some(token);
-                    }
-                    Err(lexer_error) => {
-                        panic!("{:?}", lexer_error);
-                    }
-                },
-            }
+            self.current = fetch(&mut self.lexer)?;
+            self.lookahead = fetch(&mut self.lexer)?;
+            Ok(())
         }
     }
 
-    fn expect_advance(&mut self, token_kind: TokenKind) -> Result<Token, Vec<Diagnostic>> {
+    fn join_kinds(kinds: &[TokenKind]) -> String {
+        kinds
+            .iter()
+            .map(|kind| format!("{:?}", kind))
+            .collect::<Vec<_>>()
+            .join(", ")
+    }
+
+    fn get_expected_but_found(kinds: &[TokenKind], found: &Token) -> Diagnostic {
+        Diagnostic::new(
+            &format!("Unexpected token: {:?}.", found.kind()),
+            found.start(),
+            found.end(),
+        )
+        .with_error_code(PARSE_ERROR)
+        .with_primary_label_message(&format!("Expected {}.", Self::join_kinds(kinds)))
+    }
+
+    fn get_expected_but_found_eoi(kinds: &[TokenKind], position: usize) -> Diagnostic {
+        Diagnostic::new("Unexpected end-of-input.", position, position)
+            .with_error_code(PARSE_ERROR)
+            .with_primary_label_message(&format!("Expected {}.", Self::join_kinds(kinds)))
+    }
+
+    fn expect_advance(&mut self, token_kind: TokenKind) -> Result<Token, Diagnostics> {
         match self.current.take() {
-            None => Err(vec![
-                Diagnostic::new(
-                    &format!("Expected {:?} but found end-of-input.", token_kind),
-                    self.input.len(),
-                    self.input.len(),
-                )
-                .with_reporter(file!(), line!()),
-            ]),
+            None => Err(vec![Self::get_expected_but_found_eoi(
+                &[token_kind],
+                self.input.len(),
+            )]),
             Some(token) => {
                 if token.kind() == token_kind {
-                    self.advance();
+                    self.advance()?;
                     Ok(token)
                 } else {
                     self.advance_until(&[token_kind]);
-                    Err(vec![
-                        Diagnostic::new(
-                            &format!("Expected {:?} but found {:?}", token_kind, token.kind()),
-                            token.start(),
-                            token.end(),
-                        )
-                        .with_reporter(file!(), line!()),
-                    ])
+                    Err(vec![Self::get_expected_but_found(&[token_kind], &token)])
                 }
             }
         }
     }
 
-    fn expect_position_advance(
+    fn expect_immediately_after_advance(
         &mut self,
         token_kind: TokenKind,
-        start_position: usize,
-    ) -> Result<Token, Vec<Diagnostic>> {
+        previous_token: &Token,
+    ) -> Result<Token, Diagnostics> {
         let matched = self.expect_advance(token_kind)?;
-        if matched.start() == start_position {
+        if matched.start() == previous_token.end() {
             Ok(matched)
         } else {
             Err(vec![
                 Diagnostic::new(
-                    &format!("Expected {:?} but found {:?}", token_kind, matched.kind()),
+                    &format!(
+                        "Expected {:?} immediately after previous token.",
+                        token_kind
+                    ),
                     matched.start(),
                     matched.end(),
                 )
-                .with_reporter(file!(), line!()),
+                .with_error_code(PARSE_ERROR),
             ])
         }
     }
@@ -206,13 +231,6 @@ impl<'a> Parser<'a> {
         }
     }
 
-    fn peek_lookahead(&self, token_kind: TokenKind) -> bool {
-        match &self.lookahead {
-            None => panic!("Unexpected end of input."),
-            Some(token) => token.kind() == token_kind,
-        }
-    }
-
     fn sample_input(&self, start: usize, end: usize) -> &'a str {
         &self.input[start..end]
     }
@@ -221,49 +239,40 @@ impl<'a> Parser<'a> {
         self.sample_input(token.start(), token.end())
     }
 
-    pub fn compilation_unit(&mut self) -> Result<CompilationUnit, Vec<Diagnostic>> {
+    fn compilation_unit(&mut self) -> Result<CompilationUnit, Vec<Diagnostic>> {
         let mut functions: Vec<Function> = vec![];
         let mut extern_functions: Vec<ExternFunction> = vec![];
         let mut classes: Vec<Class> = vec![];
 
         let mut diagnostics = vec![];
 
-        self.advance(); // get started
-
         while self.current.is_some() {
             let current = self.get_current();
             match current.kind() {
                 TokenKind::Fn | TokenKind::Extern | TokenKind::Class => {
-                    match self.module_level_declaration(
-                        &mut functions,
-                        &mut extern_functions,
-                        &mut classes,
-                    ) {
-                        Ok(_) => {}
-                        Err(mut declaration_diagnostics) => {
-                            diagnostics.append(&mut declaration_diagnostics)
-                        }
-                    }
+                    handle_diagnostics!(
+                        self.module_level_declaration(
+                            &mut functions,
+                            &mut extern_functions,
+                            &mut classes
+                        ),
+                        diagnostics
+                    );
                 }
                 _ => {
-                    diagnostics.push(Diagnostic::new(
-                        &format!(
-                            "Expected any of {:?}; found {:?}",
-                            [TokenKind::Fn, TokenKind::Extern, TokenKind::Class],
-                            current.kind()
-                        ),
-                        current.start(),
-                        current.end(),
+                    diagnostics.push(Self::get_expected_but_found(
+                        &[TokenKind::Fn, TokenKind::Extern, TokenKind::Class],
+                        current,
                     ));
-                    self.advance_until(&[TokenKind::Fn, TokenKind::Extern]);
+                    self.advance_until(&[TokenKind::Fn, TokenKind::Extern, TokenKind::Class]);
                 }
             }
         }
-        if diagnostics.is_empty() {
-            Ok(CompilationUnit::new(functions, extern_functions, classes))
-        } else {
-            Err(diagnostics)
-        }
+
+        ok_or_err_diagnostics!(
+            CompilationUnit::new(functions, extern_functions, classes),
+            diagnostics
+        )
     }
 
     fn module_level_declaration(
@@ -307,7 +316,7 @@ impl<'a> Parser<'a> {
 
     fn function(&mut self) -> Result<Function, Vec<Diagnostic>> {
         let is_public = if self.current.is_some() && self.peek_current(TokenKind::Public) {
-            self.advance(); // pub
+            self.advance()?; // pub
             true
         } else {
             false
@@ -356,18 +365,17 @@ impl<'a> Parser<'a> {
             _ => {}
         }
 
-        if diagnostics.is_empty() {
-            Ok(Function::new(
+        ok_or_err_diagnostics!(
+            Function::new(
                 self.token_text(&identifier_token),
                 SourceRange::new(identifier_token.start(), identifier_token.end()),
                 is_public,
                 parameters,
                 return_type,
                 statements,
-            ))
-        } else {
-            Err(diagnostics)
-        }
+            ),
+            diagnostics
+        )
     }
 
     fn extern_function(&mut self) -> Result<ExternFunction, Vec<Diagnostic>> {
@@ -399,16 +407,15 @@ impl<'a> Parser<'a> {
 
         let return_type = self.return_type()?;
 
-        if diagnostics.is_empty() {
-            Ok(ExternFunction::new(
+        ok_or_err_diagnostics!(
+            ExternFunction::new(
                 self.token_text(&identifier_token),
                 SourceRange::new(identifier_token.start(), identifier_token.end()),
                 maybe_parameters.unwrap(),
                 return_type,
-            ))
-        } else {
-            Err(diagnostics)
-        }
+            ),
+            diagnostics
+        )
     }
 
     fn class(&mut self) -> Result<Class, Vec<Diagnostic>> {
@@ -459,18 +466,17 @@ impl<'a> Parser<'a> {
 
         self.expect_advance(TokenKind::End)?;
 
-        if diagnostics.is_empty() {
-            Ok(Class::new(
+        ok_or_err_diagnostics!(
+            Class::new(
                 self.token_text(&identifier_token),
                 SourceRange::new(identifier_token.start(), identifier_token.end()),
                 generic_parameters,
                 maybe_constructor,
                 fields,
                 functions,
-            ))
-        } else {
-            Err(diagnostics)
-        }
+            ),
+            diagnostics
+        )
     }
 
     fn parameter_list(&mut self) -> Result<Vec<Parameter>, Vec<Diagnostic>> {
@@ -487,14 +493,15 @@ impl<'a> Parser<'a> {
                 }
             }
             if self.current.is_some() && self.peek_current(TokenKind::Comma) {
-                self.advance();
+                match self.advance() {
+                    Ok(_) => {}
+                    Err(mut ds) => {
+                        diagnostics.append(&mut ds);
+                    }
+                };
             }
         }
-        if diagnostics.is_empty() {
-            Ok(parameters)
-        } else {
-            Err(diagnostics)
-        }
+        ok_or_err_diagnostics!(parameters, diagnostics)
     }
 
     fn parameter(&mut self) -> Result<Parameter, Vec<Diagnostic>> {
@@ -518,7 +525,7 @@ impl<'a> Parser<'a> {
             let current = self.get_current();
             return match current.kind() {
                 TokenKind::LeftSquare => {
-                    self.advance(); // [
+                    self.advance()?; // [
                     let inner_type_use = self.type_use()?;
                     self.expect_advance(TokenKind::RightSquare)?;
                     todo!()
@@ -527,7 +534,7 @@ impl<'a> Parser<'a> {
                     let identifier_token = self.expect_advance(TokenKind::Identifier)?;
                     let generic_arguments =
                         if self.current.is_some() && self.peek_current(TokenKind::Lt) {
-                            self.advance(); // <
+                            self.advance()?; // <
                             let generic_arguments = self.generic_arguments_list()?;
                             self.expect_advance(TokenKind::Gt)?; // >
                             generic_arguments
@@ -540,19 +547,14 @@ impl<'a> Parser<'a> {
                         generic_arguments,
                     ))
                 }
-                _ => Err(vec![Diagnostic::new(
-                    &format!(
-                        "Expected LeftSquare or Identifier; found: {:?}",
-                        current.kind()
-                    ),
-                    current.start(),
-                    current.end(),
+                _ => Err(vec![Self::get_expected_but_found(
+                    &[TokenKind::LeftSquare, TokenKind::Identifier],
+                    current,
                 )]),
             };
         }
-        Err(vec![Diagnostic::new(
-            "Expected LeftSquare or Identifier; found end of input.",
-            self.input.len(),
+        Err(vec![Self::get_expected_but_found_eoi(
+            &[TokenKind::LeftSquare, TokenKind::Identifier],
             self.input.len(),
         )])
     }
@@ -562,7 +564,7 @@ impl<'a> Parser<'a> {
         while self.current.is_some() && matches_type_use_first!(self.get_current().kind()) {
             generic_arguments.push(self.type_use()?);
             if self.current.is_some() && self.peek_current(TokenKind::Comma) {
-                self.advance(); // comma
+                self.advance()?; // comma
             } else {
                 break;
             }
@@ -576,7 +578,7 @@ impl<'a> Parser<'a> {
         while self.current.is_some() && self.peek_current(TokenKind::Identifier) {
             parameters.push(self.generic_parameter()?);
             if self.current.is_some() && self.peek_current(TokenKind::Plus) {
-                self.advance(); // +
+                self.advance()?; // +
             } else {
                 break;
             }
@@ -589,11 +591,11 @@ impl<'a> Parser<'a> {
         let identifier = self.expect_advance(TokenKind::Identifier)?;
         let mut extends_list: Vec<TypeUse> = vec![];
         if self.current.is_some() && self.peek_current(TokenKind::Colon) {
-            self.advance(); // :
+            self.advance()?; // :
             while self.current.is_some() && matches_type_use_first!(self.get_current().kind()) {
                 extends_list.push(self.type_use()?);
                 if self.current.is_some() && self.peek_current(TokenKind::Comma) {
-                    self.advance(); // ,
+                    self.advance()?; // ,
                 } else {
                     break;
                 }
@@ -623,34 +625,25 @@ impl<'a> Parser<'a> {
                 }
                 _ => {
                     let lookahead = self.lookahead.as_ref().unwrap();
-                    return Err(vec![Diagnostic::new(
-                        &format!(
-                            "Expected any of {:?}; found {:?}",
-                            [TokenKind::Mut, TokenKind::Identifier, TokenKind::Fn],
-                            lookahead.kind()
-                        ),
-                        lookahead.start(),
-                        lookahead.end(),
+                    return Err(vec![Self::get_expected_but_found(
+                        &[TokenKind::Mut, TokenKind::Identifier, TokenKind::Fn],
+                        lookahead,
                     )]);
                 }
             }
             Ok(())
         } else {
             let current = self.current.as_ref().unwrap();
-            Err(vec![Diagnostic::new(
-                &format!(
-                    "Expected any of {:?}; found end-of-input.",
-                    [TokenKind::Mut, TokenKind::Identifier, TokenKind::Fn]
-                ),
-                current.end(),
-                current.end(),
+            Err(vec![Self::get_expected_but_found(
+                &[TokenKind::Mut, TokenKind::Identifier, TokenKind::Fn],
+                current,
             )])
         }
     }
 
     fn constructor(&mut self) -> Result<Constructor, Vec<Diagnostic>> {
         let is_public = if self.current.is_some() && self.peek_current(TokenKind::Public) {
-            self.advance();
+            self.advance()?;
             true
         } else {
             false
@@ -700,14 +693,14 @@ impl<'a> Parser<'a> {
 
     fn field(&mut self) -> Result<Field, Vec<Diagnostic>> {
         let is_public = if self.current.is_some() && self.peek_current(TokenKind::Public) {
-            self.advance();
+            self.advance()?;
             true
         } else {
             false
         };
 
         let is_mut = if self.current.is_some() && self.peek_current(TokenKind::Mut) {
-            self.advance();
+            self.advance()?;
             true
         } else {
             false
@@ -716,14 +709,14 @@ impl<'a> Parser<'a> {
         let identifier = self.expect_advance(TokenKind::Identifier)?;
 
         let declared_type = if self.current.is_some() && self.peek_current(TokenKind::Colon) {
-            self.advance(); // colon
+            self.advance()?; // colon
             Some(self.type_use()?)
         } else {
             None
         };
 
         let initializer = if self.current.is_some() && self.peek_current(TokenKind::Equals) {
-            self.advance(); // equals
+            self.advance()?; // equals
             Some(self.expression()?)
         } else {
             None
@@ -751,7 +744,7 @@ impl<'a> Parser<'a> {
         self.expect_advance(TokenKind::Let)?;
 
         let is_mut = if self.current.is_some() && self.peek_current(TokenKind::Mut) {
-            self.advance();
+            self.advance()?;
             true
         } else {
             false
@@ -790,7 +783,7 @@ impl<'a> Parser<'a> {
     fn bitwise_or_expression(&mut self) -> Result<Expression, Vec<Diagnostic>> {
         let mut result = self.bitwise_xor_expression()?;
         while self.current.is_some() && self.peek_current(TokenKind::Bar) {
-            self.advance(); // |
+            self.advance()?; // |
             let rhs = self.bitwise_xor_expression()?;
             let source_range =
                 SourceRange::new(result.source_range().start(), rhs.source_range().end());
@@ -807,7 +800,7 @@ impl<'a> Parser<'a> {
     fn bitwise_xor_expression(&mut self) -> Result<Expression, Vec<Diagnostic>> {
         let mut result = self.bitwise_and_expression()?;
         while self.current.is_some() && self.peek_current(TokenKind::Caret) {
-            self.advance(); // ^
+            self.advance()?; // ^
             let rhs = self.bitwise_and_expression()?;
             let source_range =
                 SourceRange::new(result.source_range().start(), rhs.source_range().end());
@@ -824,7 +817,7 @@ impl<'a> Parser<'a> {
     fn bitwise_and_expression(&mut self) -> Result<Expression, Vec<Diagnostic>> {
         let mut result = self.shift_expression()?;
         while self.current.is_some() && self.peek_current(TokenKind::Ampersand) {
-            self.advance(); // &
+            self.advance()?; // &
             let rhs = self.shift_expression()?;
             let source_range =
                 SourceRange::new(result.source_range().start(), rhs.source_range().end());
@@ -844,9 +837,9 @@ impl<'a> Parser<'a> {
             let current = self.get_current();
             match current.kind() {
                 TokenKind::Lt => {
-                    let second_lt_start = current.start() + 1;
-                    self.advance(); // first <
-                    self.expect_position_advance(TokenKind::Lt, second_lt_start)?; // second <
+                    let previous_cloned = current.clone();
+                    self.advance()?; // first <
+                    self.expect_immediately_after_advance(TokenKind::Lt, &previous_cloned)?; // second <
                     let rhs = self.additive_expression()?;
                     let source_range =
                         SourceRange::new(result.source_range().start(), rhs.source_range().end());
@@ -858,9 +851,9 @@ impl<'a> Parser<'a> {
                     ));
                 }
                 TokenKind::Gt => {
-                    let second_gt_start = current.start() + 1;
-                    self.advance(); // first >
-                    self.expect_position_advance(TokenKind::Gt, second_gt_start)?; // second gt
+                    let previous_cloned = current.clone();
+                    self.advance()?; // first >
+                    self.expect_immediately_after_advance(TokenKind::Gt, &previous_cloned)?; // second gt
                     let rhs = self.additive_expression()?;
                     let source_range =
                         SourceRange::new(result.source_range().start(), rhs.source_range().end());
@@ -883,7 +876,7 @@ impl<'a> Parser<'a> {
             let current = self.get_current();
             match current.kind() {
                 TokenKind::Plus => {
-                    self.advance(); // plus
+                    self.advance()?; // plus
                     let rhs = self.multiplicative_expression()?;
                     let source_range =
                         SourceRange::new(result.source_range().start(), rhs.source_range().end());
@@ -895,7 +888,7 @@ impl<'a> Parser<'a> {
                     ));
                 }
                 TokenKind::Minus => {
-                    self.advance(); // minus
+                    self.advance()?; // minus
                     let rhs = self.multiplicative_expression()?;
                     let source_range =
                         SourceRange::new(result.source_range().start(), rhs.source_range().end());
@@ -918,7 +911,7 @@ impl<'a> Parser<'a> {
             let current = self.get_current();
             match current.kind() {
                 TokenKind::Star => {
-                    self.advance(); // multiply
+                    self.advance()?; // multiply
                     let rhs = self.prefix_expression()?;
                     let source_range =
                         SourceRange::new(result.source_range().start(), rhs.source_range().end());
@@ -930,7 +923,7 @@ impl<'a> Parser<'a> {
                     ));
                 }
                 TokenKind::Slash => {
-                    self.advance(); // slash
+                    self.advance()?; // slash
                     let rhs = self.prefix_expression()?;
                     let source_range =
                         SourceRange::new(result.source_range().start(), rhs.source_range().end());
@@ -942,7 +935,7 @@ impl<'a> Parser<'a> {
                     ))
                 }
                 TokenKind::Modulo => {
-                    self.advance(); // modulo
+                    self.advance()?; // modulo
                     let rhs = self.prefix_expression()?;
                     let source_range =
                         SourceRange::new(result.source_range().start(), rhs.source_range().end());
@@ -967,7 +960,7 @@ impl<'a> Parser<'a> {
             match current.kind() {
                 TokenKind::Minus => {
                     operator_tokens.push(current.clone()); // unfortunately necessary
-                    self.advance();
+                    self.advance()?;
                 }
                 _ => break,
             }
@@ -1010,7 +1003,7 @@ impl<'a> Parser<'a> {
             TokenKind::IntegerLiteral => {
                 let raw = self.token_text(&current);
                 let source_range = SourceRange::new(current.start(), current.end());
-                self.advance();
+                self.advance()?;
                 Ok(Expression::Integer(IntegerLiteral::new(
                     i32::from_str(raw).unwrap(),
                     source_range,
@@ -1019,7 +1012,7 @@ impl<'a> Parser<'a> {
             TokenKind::DoubleLiteral => {
                 let raw = self.token_text(&current);
                 let source_range = SourceRange::new(current.start(), current.end());
-                self.advance();
+                self.advance()?;
                 Ok(Expression::Double(DoubleLiteral::new(
                     f64::from_str(raw).unwrap(),
                     source_range,
@@ -1028,7 +1021,7 @@ impl<'a> Parser<'a> {
             TokenKind::String => {
                 let with_quotes = self.token_text(&current);
                 let source_range = SourceRange::new(current.start(), current.end());
-                self.advance();
+                self.advance()?;
                 Ok(Expression::String(StringLiteral::new(
                     &with_quotes[1..with_quotes.len() - 1],
                     source_range,
@@ -1037,7 +1030,7 @@ impl<'a> Parser<'a> {
             TokenKind::Identifier => {
                 let declared_name = self.token_text(&current);
                 let source_range = SourceRange::new(current.start(), current.end());
-                self.advance();
+                self.advance()?;
                 Ok(Expression::Identifier(Identifier::new(
                     declared_name,
                     source_range,
@@ -1065,7 +1058,7 @@ impl<'a> Parser<'a> {
         let mut expressions = vec![];
         expressions.push(self.expression()?);
         while self.current.is_some() && self.peek_current(TokenKind::Comma) {
-            self.advance(); // comma
+            self.advance()?; // comma
             expressions.push(self.expression()?);
         }
         Ok(expressions)