enums

TODO.md

@@ -125,7 +125,14 @@
     floats follow IEEE (`fadd`/`fsub`/`fmul`/`fdiv`, no trap)
   - constant folding (global initializers) covers `-`, `*`, `/` alongside `+`
 
-7. enums (native and c interop) (see below)
+7. enums (native and c interop) (implemented; see below)
+  - native enums are nominal value types with integer runtime representations
+  - unbacked enums are non-empty, dense, zero-based, and use the smallest fitting unsigned backing
+  - explicitly backed enums require an integer type and strictly increasing literal values
+  - enum members support `Type.member`, `package.Type.member`, and contextual `.member`
+  - enum values support storage, calls/returns, and same-type equality/inequality
+  - explicitly backed native enums use their backing ABI in `c_func` signatures and variadic promotion
+  - imported C enum types alias libclang's target-selected integer backing and enumerators import as package constants
 
 8. distinct types (implemented; see below)
   - nominal declarations preserve identity across packages and reuse the backing runtime representation
@@ -255,3 +262,19 @@ Nat :: enum(u8) {
 dog_tag1 Animal :: Animal.dog
 dog_tag2 Animal :: .dog # type inferred
 ```
+
+Unbacked enums cannot assign explicit values. Backed enum values must be decimal integer
+literals, fit the backing type, and increase strictly; gaps are allowed.
+
+Native enum types remain distinct from integers and from other enum types. They support
+`==` and `!=`, but not arithmetic, ordering, casts, or backing-value extraction.
+
+C enums follow C/Zig import semantics rather than native enum semantics:
+
+```
+native :: import "native.h"
+value native.Imported_Enum :: native.IMPORTED_ENUM_VALUE
+```
+
+The imported enum type is an alias of its target-selected C integer backing, and imported
+enumerators are package-level constants.