DB<32> x map { $_ = 1 } "str"
Modification of a read-only value attempted at (eval 42)[c:/Perl_524/lib/perl5db.pl:737] line 2.
  DB<33> x map { $_ = 1 } 42
Modification of a read-only value attempted at (eval 43)[c:/Perl_524/lib/perl5db.pl:737] line 2.
  DB<34> x map { $_ = 1 } undef
Modification of a read-only value attempted at (eval 44)[c:/Perl_524/lib/perl5db.pl:737] line 2.