diff --git a/crates/fuse-parser/src/parsers/expressions.rs b/crates/fuse-parser/src/parsers/expressions.rs
index a5d7a62..7f72855 100644
--- a/crates/fuse-parser/src/parsers/expressions.rs
+++ b/crates/fuse-parser/src/parsers/expressions.rs
@@ -43,6 +43,7 @@ impl<'a> Parser<'a> {
     }
 
     pub(crate) fn parse_identifier(&mut self) -> ParserResult<Identifier> {
+        debug_assert!(self.at(TokenKind::Identifier));
         let token = self.consume();
         let view = self.view_token(*token);
         Ok(Identifier {
@@ -61,6 +62,7 @@ impl<'a> Parser<'a> {
     }
 
     fn parse_if(&mut self) -> ParserResult<If> {
+        debug_assert!(matches!(self.cur_kind(), TokenKind::If | TokenKind::ElseIf));
         let start = self.start_span();
         // Consume the keyword
         self.consume();
@@ -96,4 +98,9 @@ impl<'a> Parser<'a> {
             r#else,
         })
     }
+
+    pub(crate) fn parse_unary_operator_expression(&mut self) -> ParserResult<Expression> {
+        self.parse_unary_operator()
+            .map(|op| self.ast.unary_operator_expression(op))
+    }
 }
diff --git a/crates/fuse-parser/src/parsers/mod.rs b/crates/fuse-parser/src/parsers/mod.rs
index 51f0e7e..858e7a8 100644
--- a/crates/fuse-parser/src/parsers/mod.rs
+++ b/crates/fuse-parser/src/parsers/mod.rs
@@ -3,6 +3,7 @@ mod declarations;
 mod expressions;
 mod functions;
 mod numbers;
+mod operators;
 mod statements;
 mod strings;
 mod types;
diff --git a/crates/fuse-parser/src/parsers/operators.rs b/crates/fuse-parser/src/parsers/operators.rs
new file mode 100644
index 0000000..1ddcf87
--- /dev/null
+++ b/crates/fuse-parser/src/parsers/operators.rs
@@ -0,0 +1,31 @@
+use fuse_ast::UnaryOperator;
+
+use crate::{lexer::TokenKind, Parser, ParserResult};
+
+impl<'a> Parser<'a> {
+    pub(crate) fn parse_unary_operator(&mut self) -> ParserResult<UnaryOperator> {
+        match self.cur_kind() {
+            TokenKind::Not => self.parse_unary_not_operator(),
+            TokenKind::Plus => self.parse_unary_plus_operator(),
+            TokenKind::Minus => self.parse_unary_minus_operator(),
+            _ => Err(Self::unexpected_error(self.cur_token())),
+        }
+    }
+
+    fn parse_unary_not_operator(&mut self) -> ParserResult<UnaryOperator> {
+        debug_assert!(self.at(TokenKind::Not));
+        // Consume the keyword.
+        self.consume();
+        todo!()
+    }
+
+    fn parse_unary_plus_operator(&mut self) -> ParserResult<UnaryOperator> {
+        debug_assert!(self.at(TokenKind::Plus));
+        todo!()
+    }
+
+    fn parse_unary_minus_operator(&mut self) -> ParserResult<UnaryOperator> {
+        debug_assert!(self.at(TokenKind::Minus));
+        todo!()
+    }
+}
diff --git a/crates/fuse-parser/src/parsers/statements.rs b/crates/fuse-parser/src/parsers/statements.rs
index 31b58b2..bcf9930 100644
--- a/crates/fuse-parser/src/parsers/statements.rs
+++ b/crates/fuse-parser/src/parsers/statements.rs
@@ -62,6 +62,10 @@ impl<'a> Parser<'a> {
                 .parse_expression()
                 .map(|expr| self.ast.expression_statement(expr)),
 
+            TokenKind::Not | TokenKind::Plus | TokenKind::Minus => self
+                .parse_unary_operator_expression()
+                .map(|expr| self.ast.expression_statement(expr)),
+
             TokenKind::Function | TokenKind::Fn => {
                 if self.nth_kind(1) == TokenKind::Identifier {
                     // function declaration