kernel: Slug and Lang validated private strings

Both parse through a smart constructor returning result, and both hand-write
t_of_sexp so a malformed value in a data file is rejected at load rather than
silently accepted -- deriving the converter would have bypassed validation.

1 files changed, 11 insertions, 0 deletions

diff --git a/lib/kernel/lang.mli b/lib/kernel/lang.mli
new file mode 100644
index 0000000..6d26a1d
--- /dev/null
+++ b/lib/kernel/lang.mli
@@ -0,0 +1,11 @@
+(** Two-letter lowercase ISO-639-1 language codes. The set is deliberately open:
+    overlays add languages as data, never as code. *)
+type t = private string
+
+val of_string : string -> (t, string) result
+val of_string_exn : string -> t
+val to_string : t -> string
+val compare : t -> t -> int
+val equal : t -> t -> bool
+val t_of_sexp : Sexplib0.Sexp.t -> t
+val sexp_of_t : t -> Sexplib0.Sexp.t