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B::Concise(3)
NAME
B::Concise - Walk Perl syntax tree, printing concise info about ops
SYNOPSIS
perl -MO=Concise[,OPTIONS] foo.pl
use B::Concise qw(set_style add_callback);
DESCRIPTION
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.
EXAMPLE
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.
OPTIONS
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.
-basic
Print OPs in the order they appear in the OP tree (a preorder
traversal, starting at the root). The indentation of each OP shows its
level in the tree. This mode is the default, so the flag is included
simply for completeness.
-exec
Print OPs in the order they would normally execute (for the majority of
constructs this is a postorder traversal of the tree, ending at the
root). In most cases the OP that usually follows a given OP will appear
directly below it; alternate paths are shown by indentation. In cases
like loops when control jumps out of a linear path, a 'goto' line is
generated.
-tree
Print OPs in a text approximation of a tree, with the root of the tree
at the left and 'left-to-right' order of children transformed into
'top-to-bottom'. Because this mode grows both to the right and down, it
isn't suitable for large programs (unless you have a very wide
terminal).
-compact
Use a tree format in which the minimum amount of space is used for the
lines connecting nodes (one character in most cases). This squeezes out
a few precious columns of screen real estate.
-loose
Use a tree format that uses longer edges to separate OP nodes. This
format tends to look better than the compact one, especially in ASCII,
and is the default.
-vt Use tree connecting characters drawn from the VT100 line-drawing set.
This looks better if your terminal supports it.
-ascii
Draw the tree with standard ASCII characters like "+" 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.
-main
Include the main program in the output, even if subroutines were also
specified.
-basen
Print OP sequence numbers in base n. If n is greater than 10, the digit
for 11 will be 'a', and so on. If n is greater than 36, the digit for
37 will be 'A', and so on until 62. Values greater than 62 are not
currently supported. The default is 36.
-bigendian
Print sequence numbers with the most significant digit first. This is
the usual convention for Arabic numerals, and the default.
-littleendian
Print seqence numbers with the least significant digit first.
-concise
Use the author's favorite set of formatting conventions. This is the
default, of course.
-terse
Use formatting conventions that emulate the output of B::Terse. The
basic mode is almost indistinguishable from the real B::Terse, and the
exec mode looks very similar, but is in a more logical order and lacks
curly brackets. B::Terse doesn't have a tree mode, so the tree mode is
only vaguely reminiscient of B::Terse.
-linenoise
Use formatting conventions in which the name of each OP, rather than
being written out in full, is represented by a one- or two-character
abbreviation. This is mainly a joke.
-debug
Use formatting conventions reminiscient of B::Debug; these aren't very
concise at all.
-env
Use formatting conventions read from the environment variables
"B_CONCISE_FORMAT", "B_CONCISE_GOTO_FORMAT", and
"B_CONCISE_TREE_FORMAT".
FORMATTING SPECIFICATIONS
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.
(x(exec_text;basic_text)x)
Generates exec_text in exec mode, or basic_text in basic mode.
(*(text)*)
Generates one copy of text for each indentation level.
(*(text1;text2)*)
Generates one fewer copies of text1 than the indentation level,
followed by one copy of text2 if the indentation level is more than 0.
(?(text1#varText2)?)
If the value of var is true (not empty or zero), generates the value of
var surrounded by text1 and Text2, otherwise nothing.
#var
Generates the value of the variable var.
#varN
Generates the value of var, left jutified to fill N spaces.
~ Any number of tildes and surrounding whitespace will be collapsed to a
single space.
The following variables are recognized:
#addr
The address of the OP, in hexidecimal.
#arg
The OP-specific information of the OP (such as the SV for an SVOP, the
non-local exit pointers for a LOOP, etc.) enclosed in paretheses.
#class
The B-determined class of the OP, in all caps.
#classsym
A single symbol abbreviating the class of the OP.
#coplabel
The label of the statement or block the OP is the start of, if any.
#exname
The name of the OP, or 'ex-foo' if the OP is a null that used to be a
foo.
#extarg
The target of the OP, or nothing for a nulled OP.
#firstaddr
The address of the OP's first child, in hexidecimal.
#flags
The OP's flags, abbreviated as a series of symbols.
#flagval
The numeric value of the OP's flags.
#hyphseq
The sequence number of the OP, or a hyphen if it doesn't have one.
#label
'NEXT', 'LAST', or 'REDO' if the OP is a target of one of those in exec
mode, or empty otherwise.
#lastaddr
The address of the OP's last child, in hexidecimal.
#name
The OP's name.
#NAME
The OP's name, in all caps.
#next
The sequence number of the OP's next OP.
#nextaddr
The address of the OP's next OP, in hexidecimal.
#noise
A one- or two-character abbreviation for the OP's name.
#private
The OP's private flags, rendered with abbreviated names if possible.
#privval
The numeric value of the OP's private flags.
#seq
The sequence number of the OP. Note that this is now a sequence number
generated by B::Concise, rather than the real op_seq value (for which
see #seqnum).
#seqnum
The real sequence number of the OP, as a regular number and not
adjusted to be relative to the start of the real program. (This will
generally be a fairly large number because all of B::Concise is
compiled before your program is).
#sibaddr
The address of the OP's next youngest sibling, in hexidecimal.
#svaddr
The address of the OP's SV, if it has an SV, in hexidecimal.
#svclass
The class of the OP's SV, if it has one, in all caps (e.g., 'IV').
#svval
The value of the OP's SV, if it has one, in a short human-readable
format.
#targ
The numeric value of the OP's targ.
#targarg
The name of the variable the OP's targ refers to, if any, otherwise the
letter t followed by the OP's targ in decimal.
#targarglife
Same as #targarg, but followed by the COP sequence numbers that delimit
the variable's lifetime (or 'end' for a variable in an open scope) for
a variable.
#typenum
The numeric value of the OP's type, in decimal.
ABBREVIATIONS
OP flags abbreviations
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)
OP class abbreviations
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
Using B::Concise outside of the O framework
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.
AUTHOR
Stephen McCamant, <smcc@CSUA.Berkeley.EDU>.
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Index for
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Alphabetical
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