Handle parsing errors

scoper.mli

 open Parsetree
 
+exception Unknown_type_variable of cid
+exception Unknown_variable of id
+
 type sty =
 | Stcid of cid * sty
 | Stlist of (label * sty) list

sigmaid.ml

@@ -24,7 +24,13 @@ let main () =
     let lexbuf = Lexing.from_channel input in
     let out_fmter = Format.std_formatter in
     let prog = lex_prog lexbuf in
-    let scoped_prog = Scoper.scope prog in
+    let scoped_prog =
+      try Scoper.scope prog
+      with Scoper.Unknown_variable id ->
+        Format.eprintf "Scope error: unknown variable %s@."
+          (Scoper.string_of_id id);
+        exit 1
+    in
     let typed_prog = Typer.type_check scoped_prog in
     Format.fprintf out_fmter "#NAME %s.@\n" (Filename.chop_extension file);
     Printer.declare_labels out_fmter !Base.labels;