1 files changed, 81 insertions, 0 deletions
diff --git a/Notes/MacroHygine.md b/Notes/MacroHygine.md
new file mode 100644
index 00000000..e0f5c99b
--- /dev/null
+++ b/Notes/MacroHygine.md
@@ -0,0 +1,81 @@
+% Macro Hygine rules and notes
+
+Usecases
+=========
+
+A variable defined within the macro won't collide with one in a capture
+```rust
+macro_rules! foo {
+    ($v:expr) => {{ let a = 123; a + $v }};
+}
+
+fn bar(a: usize) -> usize {
+    // `a` here must resolve to the argument, not the macro parameter
+    foo!(a)
+}
+```
+
+Macros within functions can access values defined before the invocation
+```rust
+fn bar(a: usize) -> usize {
+    let b = 1;
+    macro_rules! foo {
+        ($v:expr) => {{ a + b + $v }};
+    }
+    let a = 123;
+    // `a` here must resolve to the local above, while the one in the macro resolves to the argument
+    foo!(a)
+}
+```
+
+
+Macros in outer scope can access any outer-scope name
+
+Identifiers introduced within macros are inaccessible outside
+```rust
+fn bar() {
+    macro_rules! foo {
+        ($v:expr) => {let a = $v;};
+    }
+
+    foo!(123);
+    //let b = a;    // ERROR
+}
+```
+
+Implementaton Notes
+===================
+
+Idea 1: Index list
+-------------------
+
+Lexer maintains a stack of counts - incremented after every TT end (closing bracket) and for every IDENT lexed. The stack grows into each TT.
+
+This stack is the hygine information for an identifier. During lookup a symbol is only usable if its hygine information is a superset or before yours.
+```
+if( item_hygine[..-1].is_subset_of(my_hygine) && item_hygine[-1] < my_hygine[item_hygine.len] ) {
+    /* allowed */
+}
+```
+
+Hygine storage points:
+- Relative paths (of the leading node)
+- Pattern bindings (variable definitions)
+- _TODO: Where else?_
+- ?Generic definitions
+- Items? (when would that be checked? They're "globally" addressable)
+
+
+Problem: Destructuring patterns end up with an incorrect hygine using this system.
+
+Idea 2: Hygine is directly related to the parser state
+--------------------------
+
+- Each lexer has a hygine tag
+- Token trees carry with them the hygine tag for the contained tokens
+- :ident captures Ident as TOK_INTERPOLATED_IDENT
+
+
+<!-- vim: ft=markdown
+-->
+