function pointers and callbacks

README.md

@@ -40,11 +40,38 @@ main :: func() void {
 }
 ```
 
-Header imports expose supported external functions, typedefs, C scalars, and
-pointers to opaque records. They never add linker inputs; implementations must
-still be supplied explicitly with the C-prefixed linking options. Set
+Header imports expose supported external functions, typedefs, C scalars, fixed
+arrays, complete plain structs and unions, function pointer typedefs, and
+pointers to opaque records. Plain records can be constructed with keyed
+literals, accessed by field, and passed or returned by value through fixed C
+signatures on `aarch64-macos`. Unsupported or incomplete records remain
+pointer-only. Header imports never add linker inputs; implementations must still
+be supplied explicitly with the C-prefixed linking options. Set
 `BROLANG_LIBCLANG_PATH` when libclang is not installed in a standard location.
 
+```bro
+native :: import "../include/native.h"
+
+pair native.Pair :: native.echo_pair(native.Pair { left = 20, right = 22 })
+choice native.Choice :: native.Choice { integer = 42 }
+```
+
+Concrete `c_func` declarations and definitions can be passed to C function
+pointer parameters. Imported C callback typedefs are nullable, so calling one
+from Brolang requires an explicit unwrap:
+
+```bro
+native :: import "../include/native.h"
+
+double :: c_func(value c_int) c_int {
+	return value + value
+}
+
+call_mapper :: func(mapper native.Imported_Mapper) c_int {
+	return mapper?(21)
+}
+```
+
 Bodyless manual and imported C functions may be variadic:
 
 ```bro
@@ -97,13 +124,14 @@ Current prototype features:
 - `#` comments
 - Immutable `::` bindings, mutable function-local `=` bindings, and `_` sinks
 - Exact-width signed/unsigned integers, `f32`, `f64`, `isize`, `usize`, and loose integer-constrained `int`
-- Target-dependent atomic `c_*` primitive types, `c_func`, and pointer-only `c_struct`
+- Target-dependent atomic `c_*` primitive types, `c_func`, and defined or opaque `c_struct`
 - Arrays, sentinel arrays, single-item pointers, many-item pointers, sentinel many-item pointers, slices, sentinel slices, strings, character literals, optionals, and native structs
 - String literals as immutable pointers to static zero-terminated byte arrays
 - Pointer-preserving `.ptr`/`.len`, pointer-to-array indexing and slicing, postfix pointer dereference and optional unwrap, and keyed struct literals
 - Contextual integer constants and compile-time folding of addition and unary negation trees
 - Directory packages with merged declarations and file-local relative imports
 - Relative C header imports as synthetic package namespaces
+- Plain imported C structs/unions, fixed arrays, and C function pointer typedefs, including keyed literals, field access, callbacks, and Apple Silicon by-value ABI lowering
 - Qualified imported globals and functions with package-aware symbol mangling
 - Demand-monomorphized Brolang and C-ABI functions
 - Bodyless concrete C function declarations with exact external symbol names