feat(parser): add parser

added a basic ast parser that is likely riddled with bugs

src/math/mod.rs

@@ -1,8 +1,12 @@
+use crate::math::types::Expression;
+
 mod lexer;
+mod parser;
 
 pub mod types;
 
-pub fn parse(source: &str) -> Vec<lexer::Token> {
+pub fn parse(source: &str) -> Expression {
     let lexer = lexer::from(source);
-    lexer.collect()
+    let mut parser = parser::from(lexer.collect());
+    parser.parse()
 }