RegExp domain types, PostgreSQL

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--PostgreSQL 9.6
--'\\' is a delimiter

create domain likely_regexp as text
    check (value ~ '^/([^/]*(\\/[^/]*)*[^\\])?/[a-z]*$');

create domain pg_regexp as text
    check (regexp_replace('', replace(substring(value from '^/(.*)/'), '\/', '/'), '', substring(value from '/([^/]*)$')) = '');

create table test_regexp (
    likely_regexp likely_regexp,
    pg_regexp     pg_regexp
);

create function test_likely_regexp(text)
returns void
language plpgsql
as $$
begin
    insert into test_regexp(likely_regexp) values ($1::likely_regexp);
exception
    when others then
    -- do nothing
end
$$;

create function test_pg_regexp(text)
returns void
language plpgsql
as $$
begin
    insert into test_regexp(pg_regexp) values ($1::pg_regexp);
exception
    when others then
    -- do nothing
end
$$;

select test_likely_regexp('/.*/g');
select test_likely_regexp('/\/.*/g');
select test_likely_regexp('/.*\/g');
select test_likely_regexp('/(/g');
select test_pg_regexp('/.*/g');
select test_pg_regexp('/\/.*/g');
select test_pg_regexp('/.*\/g');
select test_pg_regexp('/(/g');

select * from test_regexp;


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