A static typing, i.e. at compilation time, is nearly impossible.

Otherwise you'd need to type everything, including the result of functions. Even then....¹

A check at runtime is costly, that's why dynamically typed languages are slower, but easier to code.

As I already said, you could tie the variable with a self-made STORE (This, Value) function which does your checks on Value before storing it.

Attribute::Handlers has an example for Syntactic sugar to "hide" the tie-ing procedure behind an attribute.

I'm not aware of any CPAN modules already providing that, especially because there are certainly different models how to react on wrong types ( die , warn , transform, combine)

I already gave you all the links, you'd need to do it yourself for your own needs.

For instance 1E0 is a whole number in float notation, opinions will differ.

I'm saying all of this for completeness, because it's a total overkill for your problem.

There is no magic wand which can do the heavy lifting for you...

¹) Perl, like other dynamic languages, does a lot of DWIM typecasting of variables. This doesn't translate well if you want to keep it fast.

As I already said, you could tie the variable with a self-made STORE (
+This, Value) function which does your checks on Value before storing 
+it.
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allow me to clarify the above, in reference to what you said before that:

You could use Tie::Scalar to make sure that a var $x will always stay 
+an integer, by declaring STORE. But that will slow down every operati
+on on $x.
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, just use the slow Tie::Scalar to only do the validation, then store the validated integer into a "normal" variable.

Tie::Scalar whatever it can do,it's overkill to declare an integer, I do not know how to implement it, I seldom use class in my scripts.

It may be either-or, I can not have both, regex is a much general define method, I'm learning to appreciate it, since 'every perl script use regex'