implement compound and designated literals support

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@@ -175,6 +175,38 @@ e.g. for checking output for other platform:
 sexc example/sdl3-triangle.sex -C --no-platform-features --features=linux,unix,x86-64
 #+end_src
 
+** Aggregate initializers and compound literals
+~#(...)~ is a brace initializer. On its own it has no type and takes one
+from where it is written:
+
+#+begin_src scheme
+(var p (struct point) #(1 2))
+#+end_src
+
+A ~:~ inside one ends a type and makes the whole thing a compound
+literal --- an unnamed object of that type, usable anywhere an
+expression is:
+
+#+begin_src scheme
+(var q (struct point) #(struct point : 3 4))
+(var a (* int) #([int 3] : 10 20 30))
+(draw-line ui #(struct point : 0 0) end)
+(var p (* struct point) (& #(struct point : 9 9)))  ; an lvalue, so `&' works
+#+end_src
+
+The type is written as bare words, the way it is everywhere else in the
+language; ~:~ is what ends it.
+
+A leading ~.~ names a field, so initializers may be designated, given in
+any order, and mixed with positional ones:
+
+#+begin_src scheme
+(var r (struct named) #(struct named : .n 7 .first-name "zoe"))
+#+end_src
+
+A compound literal written inside a block lives until the end of that
+block and no longer, so returning its address is a dangling pointer.
+
 ** Syntactic macros
 Sex has support for syntactic macros. Macro definitions look like
 functions: they have a name, an argument list and a body. Macro should