3 files changed, 41 insertions, 0 deletions
diff --git a/lib/vcl/ast.ml b/lib/vcl/ast.ml
new file mode 100644
index 0000000..ef573c0
--- /dev/null
+++ b/lib/vcl/ast.ml
@@ -0,0 +1 @@
+type statement = Use of string
diff --git a/lib/vcl/executor.ml b/lib/vcl/executor.ml
new file mode 100644
index 0000000..5f3dd49
--- /dev/null
+++ b/lib/vcl/executor.ml
@@ -0,0 +1,21 @@
+module Make (NT : Nt.S) = struct
+  type error =
+    | ParseError of string
+    | NtError of Nt.error
+
+  let sexp_of_error e =
+    let open Sexplib.Sexp in
+    match e with
+    | ParseError s -> List [ Atom "parse-error"; Atom s ]
+    | NtError e    -> List [ Atom "nt-error"; Atom (Nt.string_of_error e) ]
+
+  let execute (ctx : Sublanguage_context.t) (stmt : Ast.statement) :
+      (Sublanguage_types.result, error) result =
+    match stmt with
+    | Ast.Use branch_name ->
+        match ctx.switch_branch branch_name with
+        | Ok delta     -> Ok (Sublanguage_types.Transition delta)
+        | Error e      -> Error (NtError e)
+
+  let _ = (module NT : Nt.S)
+end
diff --git a/lib/vcl/sublanguage.ml b/lib/vcl/sublanguage.ml
new file mode 100644
index 0000000..f9ca629
--- /dev/null
+++ b/lib/vcl/sublanguage.ml
@@ -0,0 +1,19 @@
+module Make (NT : Nt.S) = struct
+  module Exec = Executor.Make (NT)
+
+  type configuration = unit
+  type ast = Ast.statement
+  type error = Exec.error
+
+  let name = "vcl"
+  let parse _ = Ok ()
+
+  let parse_sexp = function
+    | Sexplib.Sexp.(List [ Atom "use"; Atom branch ]) -> Ok (Ast.Use branch)
+    | sexp ->
+        Error (Exec.ParseError ("unrecognized vcl command: " ^ Sexplib.Sexp.to_string sexp))
+
+  let execute = Exec.execute
+
+  let sexp_of_error = Exec.sexp_of_error
+end