Check if variable is number: Applescript

Question

How can I check if a variable is a number?

I'm trying this:

set a to 5
if a is a number
display dialog "Yes! It's a number!"
end if

I've also tried this code:

set a to 5
if a is integer
display dialog "Yes! It's a number!"
end if

But unfortunately it doesn't work as expected.

Answer 1

class of a is integer will fail if you use

set a to "5"

This will work if even if the variable is a number but was entered as text.

set a to "5"
try
    set a to a as number
    display dialog "Yes! It's a number!"
end try

Answer 2

set a to 5
if class of a is integer then
    display dialog "Yes! It's a number!"
end if

Answer 3

This is my solution:

on is_number(number_string)
    try
        set number_string to number_string as number
        return true
    on error
        return false
    end try
end is_number