feat: Add Expression definition and parsing logic.

src/ast.rs

@@ -0,0 +1,60 @@
+use crate::token::Span;
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct Expression {
+    pub kind: ExpressionKind,
+    pub span: Span,
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum ExpressionKind {
+    Integer(u64),
+    Boolean(bool),
+    Identifier(Box<str>),
+
+    Unary {
+        op: UnaryOp,
+        op_span: Span,
+        expr: Box<Expression>,
+    },
+
+    Binary {
+        op: BinaryOp,
+        op_span: Span,
+        left: Box<Expression>,
+        right: Box<Expression>,
+    },
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum UnaryOp {
+    LogicalNot,
+    BitwiseNot,
+    Negate,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum BinaryOp {
+    Add,
+    Subtract,
+    Multiply,
+    Divide,
+    Remainder,
+
+    BitwiseAnd,
+    BitwiseOr,
+    BitwiseXor,
+
+    LogicalAnd,
+    LogicalOr,
+
+    Equal,
+    Unequal,
+    LessThan,
+    LessThanOrEqual,
+    GreaterThan,
+    GreaterThanOrEqual,
+
+    Assign,
+    Member,
+}