implement type checking and constand folding for simple example

src/main.rs

@@ -1,11 +1,17 @@
 mod parser;
 mod ast;
+mod typecheck;
+mod constfold;
 
 fn main() {
     let input = include_str!("../test.hw");
     let result = parser::parse(input);
     match result {
-        Ok(script) => {dbg!(script);},
+        Ok(mut script) => {
+            constfold::fold_script(&mut script);
+            typecheck::tc_script(&mut script).unwrap();
+            dbg!(script);
+        },
         Err(err) => println!("error: {}", nom::error::convert_error(input, err))
     }
 }