Your use of uc is what is causing your problem I think:

#! perl -slw
use strict;

my @types = qw(
  date
  integer
  text
  timestamp
);

foreach my $type (@types) {
    my $function = uc $type;
    no strict 'refs';
    *$function = sub {
        # line 1 "$type.anon"
        if ( looks_like_number( $_[0] ) ) {
            die "Datatype '$type' does not require a numeric length '$
+_[0]'";
        }
        return { type => $type, @_ };
    };
    print *$function;
}
__END__
C:\test>junk6
*main::DATE
*main::INTEGER
*main::TEXT
*main::TIMESTAMP
[download]

Remove it and you get:

C:\test>junk6
*main::date
*main::integer
*main::text
*main::timestamp
[download]

Is that what you are after?