feat: Add parsing for expressions.

This commit adds support for parsing expression using the pratt parsing
approach.

src/main.rs

@@ -2,11 +2,14 @@ use std::fs;
 
 use crate::{
     cli::{fatal, parse_args},
-    lexer::Lexer,
+    parser::Parser,
 };
 
+mod ast;
 mod cli;
+mod diagnostic;
 mod lexer;
+mod parser;
 mod token;
 
 fn main() {
@@ -25,8 +28,11 @@ fn main() {
         };
 
         println!("-- {} --", file.display());
-        for token in Lexer::new(&content) {
-            println!("{}", token);
+        let mut parser = Parser::new(&content);
+
+        match parser.parse_expression(0) {
+            Ok(ast) => println!("{ast:#?}"),
+            Err(diag) => diag.report(file, &content),
         }
     }
 }