Always check out the latest perl5-porters discussions on these subjects
before embarking on an implementation tour.

Tie Modules
	VecArray		Implement array using vec()
	SubstrArray		Implement array using substr()
	VirtualArray		Implement array using a file
	ShiftSplice		Defines shift et al in terms of splice method

Would be nice to have
	pack "(stuff)*", "(stuff)?", "(stuff)+", "(stuff)4", ...
	contiguous bitfields in pack/unpack
	lexperl
	bundled perl preprocessor/macro facility
	    this would solve many of the syntactic nice-to-haves
	use posix calls internally where possible
	gettimeofday (possibly best left for a module?)
	format BOTTOM
	-i rename file only when successfully changed
	all ARGV input should act like <>
	report HANDLE [formats].
	support in perlmain to rerun debugger
	regression tests using __DIE__ hook
	lexically scoped functions: my sub foo { ... }
        wantlvalue?  more generalized want()/caller()?
	named prototypes: sub foo ($foo, @bar) { ... } ?
	regression/sanity tests for suidperl
	iterators/lazy evaluation/continuations/first/
	    first_defined/short-circuiting grep/??
	    This is a very thorny and hotly debated subject,
	    tread carefully and do your homework first
	generalise Errno way of extracting cpp symbols and use that in
	    Errno, Fcntl, POSIX (ExtUtils::CppSymbol?)
	the _r-problem: for all the {set,get,end}*() system database
	     calls (and a couple more: readdir, *rand*, crypt, *time,
	     tmpnam) there are in many systems the _r versions
	     to be used in re-entrant (=multithreaded) code
	     Icky things: the _r API is not standardized and
	     the _r-forms require per-thread data to store their state
	memory profiler: turn malloc.c:Perl_get_mstats() into
	    an extension (Devel::MProf?) that would return the malloc
	    stats in a nice Perl datastructure (also a simple interface
	    to return just the grand total would be good)
	a way to make << and >> to shift bitvectors instead of numbers

Possible pragmas
	debugger
	optimize (use less qw[memory cpu])

Optimizations
	constant function cache
	switch structures
	foreach(reverse...)
	cache eval tree (unless lexical outer scope used (mark in &compiling?))
	rcatmaybe
	shrink opcode tables via multiple implementations selected in peep
	cache hash value?  (Not a win, according to Guido)
	optimize away @_ where possible
	tail recursion removal
	"one pass" global destruction
	rewrite regexp parser for better integrated optimization
	LRU cache of regexp: foreach $pat (@pats) { foo() if /$pat/ }

Vague possibilities
	ref function in list context?
	make tr/// return histogram in list context?
	loop control on do{} et al
	explicit switch statements
	built-in globbing
	compile to real threaded code
	structured types
	autocroak?
	modifiable $1 et al
