add helper functions chars

planet/System.ocg/String.c

@@ -19,4 +19,34 @@ global func TakeString(string str, int begin, int end)
 	for (var index = begin; index < end; index++)
 		reduced_str = Format("%s%c", reduced_str, GetChar(str, index));
 	return reduced_str;
-}
+}
+
+// Converts a char into a string.
+global func CharToString(int char)
+{
+	return Format("%c", char);
+}
+
+// Returns whether a char is a digit [0-9].
+global func CharIsDigit(int char)
+{
+	return Inside(char, 48, 57);
+}
+
+// Returns whether a char is a letter [A-Za-z].
+global func CharIsLetter(int char)
+{
+	return CharIsLowerCase(char) || CharIsUpperCase(char);
+}
+
+// Returns whether a char is a lower-case letter [a-z].
+global func CharIsLowerCase(int char)
+{
+	return Inside(char, 97, 122);
+}
+
+// Returns whether a char is an upper-case letter [A-Z].
+global func CharIsUpperCase(int char)
+{
+	return Inside(char, 65, 90);
+}