Improve exception output of SCAN_Name on bad input

1 files changed, 5 insertions, 3 deletions

diff --git a/src/libstate/scan_name.cpp b/src/libstate/scan_name.cpp
index 9e046e8ea..ded1e97b7 100644
--- a/src/libstate/scan_name.cpp
+++ b/src/libstate/scan_name.cpp
@@ -71,6 +71,8 @@ SCAN_Name::SCAN_Name(const std::string& algo_spec)
    u32bit level = 0;
    std::pair<u32bit, std::string> accum = std::make_pair(level, "");
 
+   std::string decoding_error = "Bad SCAN name '" + algo_spec + "': ";
+
    for(u32bit i = 0; i != algo_spec.size(); ++i)
       {
       char c = algo_spec[i];
@@ -82,7 +84,7 @@ SCAN_Name::SCAN_Name(const std::string& algo_spec)
          else if(c == ')')
             {
             if(level == 0)
-               throw Decoding_Error("Bad SCAN name " + algo_spec);
+               throw Decoding_Error(decoding_error + "Mismatched parens");
             --level;
             }
 
@@ -103,7 +105,7 @@ SCAN_Name::SCAN_Name(const std::string& algo_spec)
       name.push_back(deref_aliases(accum));
 
    if(level != 0 || name.size() == 0)
-      throw Decoding_Error("Bad SCAN name " + algo_spec);
+      throw Decoding_Error(decoding_error + "Empty name");
 
    alg_name = name[0].second;
 
@@ -146,7 +148,7 @@ std::string SCAN_Name::algo_name_and_args() const
 std::string SCAN_Name::arg(u32bit i) const
    {
    if(i >= arg_count())
-      throw std::range_error("SCAN_Name::argument");
+      throw std::range_error("SCAN_Name::argument - i out of range");
    return args[i];
    }