Isnum()
isnum(<string>)
This function will return 1 (TRUE) if the argument is a valid number and 0 (FALSE) otherwise. This definition of a number includes scientific notation as well as a certain case-insensitive 'special words': NaN, -Inf, +Inf, and Ind.
You can test more restrictively with israt() or isint().
Example
> say isnum(22223.0000)
You say "1"
> say isnum(10E-20)
You say "1"
> say isnum(+77)
You say "1"
>say isnum(+Inf)
You say "1"
> say isnum(22 L)
You say "0"
>say isnum(Bad Numbers!)
You say "0"