I know that perl6 has / will have lazy strings, since (in S32::Containers) the List role defines a cat method, which returns a Cat object, which "does the Str interface, but generates the string lazily."
First, are Cat objects documented anywhere else? Secondly, if a regular expression match is done on a lazy string, is that lazy string turned into a normal string? If we can efficiently match against a lazy string, and if this doesn't turn the lazy string into a (large) normal string, then the best way to process a file might be something similar to: my $fh = open ... err die; my $contents = cat($fh.lines); , followed by matching on $contents. Better still would be to provide a way for filehandles to be directly asked to produce a lazy Str which reflects the file.
