Problem

You have a text input that should look like an email address. You want a bool answer: is it valid?

Solution 

module validation;

pub fn is_email(s: text) -> bool {
    return re::matches(s, /^[\w.+-]+@[\w-]+\.[\w.-]+$/);
}

re::matches returns bool. The pattern anchors with ^...$ so the entire input has to match — partial matches don’t count.

How it lowers 

CREATE OR REPLACE PACKAGE validation AS
  FUNCTION is_email(p_s IN VARCHAR2) RETURN BOOLEAN;
END validation;
/

CREATE OR REPLACE PACKAGE BODY validation AS
  FUNCTION is_email(p_s IN VARCHAR2) RETURN BOOLEAN IS
  BEGIN
    RETURN pell_re.matches(p_s, '^[\w.+-]+@[\w-]+\.[\w.-]+$');
  END is_email;
END validation;
/

Use it 

if is_email("alice@example.com") {
    log::info("looks good");
}

if !is_email("not-an-email") {
    log::info("nope");
}

A more honest email regex

RFC 5322 is a tar pit. For most applications, the pattern above is sufficient. If you want to match the spec more closely (at the cost of complexity), use a richer pattern:

pub fn is_email_strict(s: text) -> bool {
    return re::matches(s, /^[\w!#$%&'*+\/=?^`{|}~.-]+@[\w-]+(\.[\w-]+)+$/);
}

For production, prefer structural validation (presence of @, exactly one of them, domain has a .) over regex perfection — and do the real validation by sending a confirmation email.

Returning Option instead

If you want to keep the validated value:

pub fn parse_email(s: text) -> Option<text> {
    if re::matches(s, /^[\w.+-]+@[\w-]+\.[\w.-]+$/) {
        return Some(lower(s));      // normalize to lowercase
    }
    return None;
}

See also