Handle negative numbers in JSONParse::parse_number

- fix issue #334, where negative numbers loaded from JSON were being
  parsed as 0.
- add unit tests to cover these cases.

include/chaiscript/utility/json.hpp

@@ -567,10 +567,13 @@ struct JSONParser {
     std::string val, exp_str;
     char c = '\0';
     bool isDouble = false;
+    bool isNegative = false;
     long exp = 0;
     for (; offset < str.size() ;) {
       c = str[offset++];
-      if( (c == '-') || (c >= '0' && c <= '9') ) {
+      if( c == '-' ) {
+        isNegative = true;
+      } else if( c >= '0' && c <= '9' ) {
         val += c;
       } else if( c == '.' ) {
         val += c; 
@@ -608,12 +611,12 @@ struct JSONParser {
     --offset;
 
     if( isDouble ) {
-      return JSON(chaiscript::parse_num<double>( val ) * std::pow( 10, exp ));
+      return JSON((isNegative?-1:1) * chaiscript::parse_num<double>( val ) * std::pow( 10, exp ));
     } else {
       if( !exp_str.empty() ) {
-        return JSON(static_cast<double>(chaiscript::parse_num<long>( val )) * std::pow( 10, exp ));
+        return JSON((isNegative?-1:1) * static_cast<double>(chaiscript::parse_num<long>( val )) * std::pow( 10, exp ));
       } else {
-        return JSON(chaiscript::parse_num<long>( val ));
+        return JSON((isNegative?-1:1) * chaiscript::parse_num<long>( val ));
       }
     }
   }

unittests/json_3.chai

@@ -1 +1,2 @@
 assert_equal(from_json("100"), 100)
+assert_equal(from_json("-100"), -100)

unittests/json_4.chai

@@ -1 +1,2 @@
 assert_equal(from_json("1.234"), 1.234)
+assert_equal(from_json("-1.234"), -1.234)

unittests/json_9.chai

@@ -1,2 +1,2 @@
-assert_equal(from_json("[1,2,3]"), [1,2,3])
+assert_equal(from_json("[1,-2,3]"), [1,-2,3])