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(** Envelope parser for tagged S-expressions.
Parses commands of the form (tag payload...) where the tag selects which
sublanguage handles the payload. The tag set is open — future sublanguages
(tcl, ppl, acl) just add new tags. *)
type tagged = { tag : string; payload : Sexplib.Sexp.t }
let parse (input : Sexplib.Sexp.t) : (tagged, Error.t) Result.t =
match input with
| Sexplib.Sexp.List (Sexplib.Sexp.Atom tag :: rest) ->
let payload = match rest with
| [single] -> single
| many -> Sexplib.Sexp.List many
in
Ok { tag; payload }
| s -> Error (Error.MalformedExpression s)
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