add notes for executor

executor/src/lib.rs

@@ -19,5 +19,30 @@ pub fn run_program(module: Module) -> Result<()> {
     };
 
     println!("main {:?}", main);
+
+    // loop through all variables and check if
+    // runtime computation should be executed
+    // actually a big problem and should be done later
+    // this requires dependency tree (DAG) of lazy variables
+
+    // in the mean time, we can use the logic of lazy evaluation
+    // (Haskell). By only execute the variable when a computation
+    // requires. However, we might not cache the result.
+
+    // type checks, everything should be checked because this is
+    // a statically typed language. We do not tolerate any type errors.
+    // this will be implemented in another package "type"
+
+    // the whole context will be intialized and passed through each
+    // computation.
+
+    // We allow for callable objects, these include closure, partial
+    // application. This will be reflected in the runtime by replacing
+    // variable values into the Expression and when fully apply,
+    // the Expression is evaluated to get the result.
+
+    // Advanced features will be designed and implemented at a later
+    // stage into development.
+
     Ok(())
 }