mu: sexp-parser: add support for negative numbers

We need those too!

lib/utils/mu-sexp-parser.cc

@@ -106,10 +106,15 @@ parse_string (const std::string& expr, size_t& pos)
 static Node
 parse_integer (const std::string& expr, size_t& pos)
 {
-        if (!isdigit(expr[pos])) // sanity check.
+        if (!isdigit(expr[pos]) && expr[pos] != '-') // sanity check.
                 throw parsing_error(pos, "expected: <digit> but got '%c", expr[pos]);
 
-        std::string num;
+        std::string num; // negative number?
+        if (expr[pos] == '-') {
+                num = "-";
+                ++pos;
+        }
+
         for (; isdigit(expr[pos]); ++pos)
                 num += expr[pos];
 
@@ -144,7 +149,7 @@ parse (const std::string& expr, size_t& pos)
                         return parse_list (expr, pos);
                 else if (kar == '"')
                         return parse_string(expr, pos);
-                else if (isdigit(kar))
+                else if (isdigit(kar) || kar == '-')
                         return parse_integer(expr, pos);
                 else if (isalpha(kar) ||  kar == ':')
                         return parse_symbol(expr, pos);

lib/utils/test-sexp-parser.cc

@@ -48,6 +48,7 @@ test_parser()
         check_parse(R"(:foo-123)", "<symbol>{:foo-123}");
         check_parse(R"("foo")",    "<string>{foo}");
         check_parse(R"(12345)",    "<integer>{12345}");
+        check_parse(R"(-12345)",   "<integer>{-12345}");
         check_parse(R"((123 bar "cuux"))",    "<list>(<integer>{123}<symbol>{bar}<string>{cuux})");
 
         check_parse(R"("\"")", "<string>{\"}");