initial commit wip0

examples/stacked_borrows.rs

+// Stacked borrows, Proof of Concept
+use std::collections::{HashMap, VecDeque};
+
+type Id = String;
+
+type Stack = VecDeque<Item>;
+
+type Env = HashMap<Id, Tag>;
+
+type Tag = u32;
+
+#[derive(Debug)]
+enum Item {
+    Unique(Tag),
+    SharedRO(Tag),
+    SharedRW(Tag),
+}
+
+#[derive(Debug)]
+struct Store {
+    tag: Tag,
+    stack: Stack,
+    env: Env,
+}
+
+impl Store {
+    fn new() -> Store {
+        Store {
+            tag: 0,
+            stack: Stack::new(),
+            env: Env::new(),
+        }
+    }
+    fn alloc(&mut self, id: Id) {
+        self.stack.push_front(Item::Unique(self.tag));
+        self.tag += 1;
+    }
+}
+
+#[derive(Debug)]
+enum Expr {
+    Id(Id),
+    Num(i32),
+    Ref(Box<Expr>),
+    RefMut(Box<Expr>),
+    Deref(Box<Expr>),
+}
+
+#[derive(Debug)]
+enum Stmt {
+    Let(Id, Expr), // assumed mutable, e.g. let mut a = 0;
+    Assign(Expr, Expr),
+}
+
+fn left_expr(e: &Expr) -> &Id {
+    match e {
+        Expr::Id(id) => id,
+        Expr::Deref(e) => left_expr(e),
+        _ => unimplemented!("illegal left hand"),
+    }
+}
+
+fn check_stmt(s: &Stmt, store: &mut Store) {
+    match s {
+        Stmt::Let(id, e) => store.alloc(id.to_owned()),
+        Stmt::Assign(le, re) => {}
+    }
+}
+
+fn check_stmts(v: &Vec<Stmt>, store: &mut Store) {
+    for s in v {
+        check_stmt(&s, store);
+    }
+}
+
+fn main() {
+    let mut env = Env::new();
+    use {Expr::*, Stmt::*};
+    let v = vec![Let("a".to_owned(), Num(0))];
+    
+    check_stmts(&v, &mut Store::new());
+}