STL rework

- fixed lots of bugs
- overlay libraries work correctly and reliably
- the STL is an overlay library
- examples updated

src/utils/substack.rs

@@ -41,17 +41,13 @@ impl<'a, T> Substack<'a, T> {
   }
   /// Create a new frame on top of this substack
   pub fn new_frame(&'a self, item: T) -> Stackframe<'a, T> {
-    Stackframe { item, prev: self, len: self.opt().map_or(1, |s| s.len) }
+    Stackframe { item, prev: self, len: self.opt().map_or(1, |s| s.len + 1) }
   }
   /// obtain the previous stackframe if one exists
   /// TODO: this should return a [Substack]
   pub fn pop(&'a self, count: usize) -> Option<&'a Stackframe<'a, T>> {
     if let Self::Frame(p) = self {
-      if count == 0 {
-        Some(p)
-      } else {
-        p.prev.pop(count - 1)
-      }
+      if count == 0 { Some(p) } else { p.prev.pop(count - 1) }
     } else {
       None
     }