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sx/examples/packs/0534-packs-pack-type-projection.sx
agra 66bdc70bf1 test: group examples into per-category folders
Move examples/*.sx and their expected/ snapshots into per-category
subfolders (examples/<category>/...). Folder = leading filename token,
with ffi-objc/ffi-jni kept whole; filenames are unchanged. The corpus
runner and LSP sweep now discover each category's expected/ dir, while
issues/ stays flat. Example 1058's repo-root-relative companion import
is made file-relative. Path strings embedded in 164 snapshots were
regenerated (path-only changes). Test-layout docs in CLAUDE.md updated.
2026-06-21 14:41:34 +03:00

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// Feature 1 — TYPE-position pack projection `xs.T`. The per-element protocol
// type-arg `T` projects into a Pack of types, usable in type/signature
// positions: a tuple type `(..xs.T)` and a closure signature
// `Closure(..xs.T) -> R`. (`T` of each element comes from its
// `impl Box(T) for <elem>`.)
#import "modules/std.sx";
Box :: protocol(T: Type) {
get :: (self: *Self) -> T;
}
IntCell :: struct { v: i64; }
StrCell :: struct { s: string; }
Dbl :: struct { n: i64; }
impl Box(i64) for IntCell { get :: (self: *IntCell) -> i64 => self.v; }
impl Box(string) for StrCell { get :: (self: *StrCell) -> string => self.s; }
impl Box(i64) for Dbl { get :: (self: *Dbl) -> i64 => self.n * 2; }
// Tuple type `(..xs.T)` — heterogeneous (i64, string), matched by the
// value-projection `(..xs.get)`.
snap :: (..xs: Box) -> void {
t : (..xs.T) = (..xs.get);
print("0={} 1={}\n", t.0, t.1);
}
// Closure signature `Closure(..xs.T) -> i64` — here `Closure(i64, i64) -> i64`.
// The closure literal's params are contextually typed from the projection.
fold :: (..xs: Box) -> i64 {
cb : Closure(..xs.T) -> i64 = (a, b) => a + b;
return cb(xs[0].get(), xs[1].get());
}
main :: () -> i32 {
snap(IntCell.{ v = 42 }, StrCell.{ s = "hi" }); // (i64, string)
print("fold={}\n", fold(IntCell.{ v = 10 }, Dbl.{ n = 5 })); // 10 + 10 = 20
0
}