Add namespacing doc

docs/namespacing.md

@@ -0,0 +1,61 @@
+# Namespacing
+
+In order to work with C's namespace limitations, I've designed the following
+system:
+
+## Namespaces
+
+In C, there is a GCC extension (also supported by clang and TCC) to allow for
+dollar signs in identifiers. This provides a way to have compiled C code which
+segments its imports into different namespaces. For example `Foo$Baz` would be
+the identifier `Baz` in the namespace `Foo`, and would be guaranteed to not
+collide with a user-chosen name like `FooBaz`.
+
+```
+// File: foo.nl
+struct Baz(x:Int)
+    member := 5
+    func frob(b:Baz)->Int
+        return b.x
+
+qux := "Loaded!"
+say(qux)
+
+// File: foo.nl.h
+...
+typedef struct foo$Baz_s foo$Baz_t;
+#define foo$Baz(...) (foo$Baz_t){__VA_ARGS__}
+struct foo$Baz_s {
+    Int_t x;
+};
+extern Int_t foo$Baz$member;
+Int_t foo$Baz$frob(foo$Baz_t b);
+...
+
+// File: foo.nl.c
+#include "foo.nl.h"
+Int_t foo$Baz$member = 5;
+
+Int_t foo$Baz$frob(foo$Baz_t b) {
+    return b.x;
+}
+
+void use$foo(void) {
+    static enum {UNLOADED, LOADING, LOADED} $state = UNLOADED;
+    if ($state == LOADING)
+        fail("Circular import");
+    else if ($state == LOADED)
+        return;
+
+    $state = LOADING;
+    { // Top-level code:
+        Str qux = "Loaded!";
+        say(qux);
+    }
+    $state = LOADED;
+}
+```
+
+And on the usage site, the code `use ./foo.tm` compiles to `#include
+"./foo.tm.h"` in the header and `use$foo()` in the code that is executed.
+