| B::Concise - Walk Perl syntax tree, printing concise info about ops |
B::Concise - Walk Perl syntax tree, printing concise info about ops
perl -MO=Concise[,OPTIONS] foo.pl
use B::Concise qw(set_style add_callback);
This compiler backend prints the internal OPs of a Perl program's syntax tree in one of several space-efficient text formats suitable for debugging the inner workings of perl or other compiler backends. It can print OPs in the order they appear in the OP tree, in the order they will execute, or in a text approximation to their tree structure, and the format of the information displyed is customizable. Its function is similar to that of perl's -Dx debugging flag or the B::Terse module, but it is more sophisticated and flexible.
Here's is a short example of output, using the default formatting conventions :
% perl -MO=Concise -e '$a = $b + 42'
8 <@> leave[1 ref] vKP/REFC ->(end)
1 <0> enter ->2
2 <;> nextstate(main 1 -e:1) v ->3
7 <2> sassign vKS/2 ->8
5 <2> add[t1] sK/2 ->6
- <1> ex-rv2sv sK/1 ->4
3 <$> gvsv(*b) s ->4
4 <$> const(IV 42) s ->5
- <1> ex-rv2sv sKRM*/1 ->7
6 <$> gvsv(*a) s ->7
Each line corresponds to an operator. Null ops appear as ex-opname,
where opname is the op that has been optimized away by perl.
The number on the first row indicates the op's sequence number. It's given in base 36 by default.
The symbol between angle brackets indicates the op's type : for example, <2> is a BINOP, <@> a LISTOP, etc. (see OP class abbreviations).
The opname may be followed by op-specific information in parentheses
(e.g. gvsv(*b)), and by targ information in brackets (e.g.
leave[t1]).
Next come the op flags. The common flags are listed below
(OP flags abbreviations). The private flags follow, separated
by a slash. For example, vKP/REFC means that the leave op has
public flags OPf_WANT_VOID, OPf_KIDS, and OPf_PARENS, and the private
flag OPpREFCOUNTED.
Finally an arrow points to the sequence number of the next op.
Arguments that don't start with a hyphen are taken to be the names of
subroutines to print the OPs of; if no such functions are specified,
the main body of the program (outside any subroutines, and not
including use'd or require'd files) is printed. Passing BEGIN,
CHECK, INIT, or END will cause all of the corresponding
special blocks to be printed.
+ and |. These don't
look as clean as the VT100 characters, but they'll work with almost any
terminal (or the horizontal scrolling mode of less(1)) and are suitable
for text documentation or email. This is the default.
B_CONCISE_FORMAT, B_CONCISE_GOTO_FORMAT, and B_CONCISE_TREE_FORMAT.
For each general style ('concise', 'terse', 'linenoise', etc.) there are three specifications: one of how OPs should appear in the basic or exec modes, one of how 'goto' lines should appear (these occur in the exec mode only), and one of how nodes should appear in tree mode. Each has the same format, described below. Any text that doesn't match a special pattern is copied verbatim.
The following variables are recognized:
v OPf_WANT_VOID Want nothing (void context)
s OPf_WANT_SCALAR Want single value (scalar context)
l OPf_WANT_LIST Want list of any length (list context)
K OPf_KIDS There is a firstborn child.
P OPf_PARENS This operator was parenthesized.
(Or block needs explicit scope entry.)
R OPf_REF Certified reference.
(Return container, not containee).
M OPf_MOD Will modify (lvalue).
S OPf_STACKED Some arg is arriving on the stack.
* OPf_SPECIAL Do something weird for this op (see op.h)
0 OP (aka BASEOP) An OP with no children
1 UNOP An OP with one child
2 BINOP An OP with two children
| LOGOP A control branch OP
@ LISTOP An OP that could have lots of children
/ PMOP An OP with a regular expression
$ SVOP An OP with an SV
" PVOP An OP with a string
{ LOOP An OP that holds pointers for a loop
; COP An OP that marks the start of a statement
# PADOP An OP with a GV on the pad
It is possible to extend B::Concise by using it outside of the O framework and providing new styles and new variables.
use B::Concise qw(set_style add_callback);
set_style($format, $gotofmt, $treefmt);
add_callback
(
sub
{
my ($h, $op, $level, $format) = @_;
$h->{variable} = some_func($op);
}
);
B::Concise::compile(@options)->();
You can specify a style by calling the set_style subroutine. If you have a new variable in your style, or you want to change the value of an existing variable, you will need to add a callback to specify the value for that variable.
This is done by calling add_callback passing references to any callback subroutines. The subroutines are called in the same order as they are added. Each subroutine is passed four parameters. These are a reference to a hash, the keys of which are the names of the variables and the values of which are their values, the op, the level and the format.
To define your own variables, simply add them to the hash, or change existing values if you need to. The level and format are passed in as references to scalars, but it is unlikely that they will need to be changed or even used.
To switch back to one of the standard styles like concise or
terse, use set_style_standard.
To see the output, call the subroutine returned by compile in the same way that O does.
Stephen McCamant, <smcc@CSUA.Berkeley.EDU>.
| B::Concise - Walk Perl syntax tree, printing concise info about ops |