1 files changed, 19 insertions, 0 deletions
diff --git a/lib/label.ml b/lib/label.ml
new file mode 100644
index 0000000..acc3e49
--- /dev/null
+++ b/lib/label.ml
@@ -0,0 +1,19 @@
+type t = string
+
+let is_lower c = c >= 'a' && c <= 'z'
+
+let is_body c =
+  is_lower c || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') || c = '_'
+
+let well_formed s =
+  String.length s > 0
+  && is_lower s.[0]
+  && String.for_all is_body s
+
+let of_string s = if well_formed s then Ok s else Error (`Invalid_label s)
+let to_string t = t
+let equal = String.equal
+let compare = String.compare
+let pp fmt t = Format.fprintf fmt "%s:" t
+
+module Map = Map.Make (String)