Hi Adrian, > On 10 Oct 2011, at 19:56, Ralph Corderoy wrote: > > A nice description of Lua 5's implementation, including its hybrid > > hash-table/array implementation, and using a register-based VM > > compared to its earlier stack-based VM as Python and Perl still use. > > http://www.jucs.org/jucs_11_7/the_implementation_of_lua/jucs_11_7_1159_1176_defigueiredo.html > > Niggle ;-)
You're among pedants here. :-) > Perl 4/5 doesn't really have a VM per se. The code is turned into a > syntax tree that's then walked at runtime. See > http://perldoc.perl.org/perlcompile.html. Yes, you're right, it does walk the syntax tree and not turn it into bytecode that's then run on the VM, like Python, I should have been more precise. But the operations carried out are at the level of bytecode instructions, and they operate on a data stack, e.g. `multiply' pops the top two items and pushes the result so I still think the evaluation is stack-based rather than Lua's registers or Parrot. Here's the stack contents and the operation from perl's -D option that I've then annotated on the right. $ perl -Dst -e 'sub f() {my($a, $b) = @_; $a * 42 + $b} &f(9, 13)' 2>&1 | > expand | > awk '/=>/ {printf "%-44s", $0; next} 1' | > sed -n '/=>/s/(-e:.) *//p' => enter => nextstate => pushmark => * const(IV(9)) => * IV(9) const(IV(13)) => * IV(9) IV(13) gv(main::f) => * IV(9) IV(13) GV() entersub # &f(9, 13) => IV(9) IV(13) nextstate => pushmark => * gv(main::_) => * GV() rv2av => * IV(9) IV(13) pushmark => * IV(9) IV(13) * padsv($a) => * IV(9) IV(13) * UNDEF padsv($b) => * IV(9) IV(13) * UNDEF UNDEF aassign # my($a, $b) = @_ => nextstate => padsv($a) => IV(9) const(IV(42)) => IV(9) IV(42) multiply # $a * 42 => IV(378) padsv($b) => IV(378) IV(13) add # ... + $b => IV(391) leavesub => IV(391) leave $ And for completeness, Python's bytecode. >>> from dis import dis >>> def f(a, b): return a * 42 + b ... >>> def g(): f(9, 13) ... >>> dis(f) 1 0 LOAD_FAST 0 (a) 3 LOAD_CONST 1 (42) 6 BINARY_MULTIPLY 7 LOAD_FAST 1 (b) 10 BINARY_ADD 11 RETURN_VALUE >>> dis(g) 1 0 LOAD_GLOBAL 0 (f) 3 LOAD_CONST 1 (9) 6 LOAD_CONST 2 (13) 9 CALL_FUNCTION 2 12 POP_TOP 13 LOAD_CONST 0 (None) 16 RETURN_VALUE >>> Cheers, Ralph. -- Next meeting: Bournemouth, Tuesday 2011-11-01 20:00 Meets, Mailing list, IRC, LinkedIn, ... http://dorset.lug.org.uk/ How to Report Bugs Effectively: http://goo.gl/4Xue
