Use this macro to decide that a string contains integer value or not. This can beuseful implementing operators that work with doubles as well as longs. When one of the operators is a string hopefully containing the decimal form of a number you have to convert the string to a long or double. This macro calls a function that decides whether the string contains an integer number convertible to long or contains a double.
For an example how to use it see the source file commands/mathops.c