_e: throw error when vspace does not exist

shell/e.cpp

@@ -1,6 +1,7 @@
 #include "shell.h"
 #include "parser.h"
 #include "commands.h"
+#include "errors.h"
 
 #include <fmt/core.h>
 #include <optional>
@@ -18,15 +19,25 @@ struct _e_args
 static _e_args parse_e(Session &session, Parser &parser)
 {
     _e_args args {};
+
     parser.option("vspace",
         [&args](std::string const &value) { args.space_name = value; });
 
-    VirtualSpace *space = session.get_space(args.space_name);
-    if(space) {
-        while(!parser.at_end()) {
+    parser.accept_options();
+
+    VirtualSpace *space;
+    if (!args.space_name.empty())
+        space = session.get_space(args.space_name);
+    else
+        space = session.current_space;
+
+    if (space)
+        while(!parser.at_end())
             args.values.push_back(parser.expr(space));
-        }
-    }
+    else
+        throw CommandError("virtual space {} does not exist",
+                           args.space_name);
+
     // TODO: Error message when session specified in _e does not exist
 
     parser.end();