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B::Concise(3pm)	       Perl Programmers Reference Guide	       B::Concise(3pm)

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 displayed 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 two outputs (or 'renderings'), using the -exec and -basic (i.e.
       default) formatting conventions on the same code snippet.

	   % perl -MO=Concise,-exec -e '$a = $b + 42'
	   1  <0> enter
	   2  <;> nextstate(main 1 -e:1) v
	   3  <#> gvsv[*b] s
	   4  <$> const[IV 42] s
	*  5  <2> add[t3] sK/2
	   6  <#> gvsv[*a] s
	   7  <2> sassign vKS/2
	   8  <@> leave[1 ref] vKP/REFC

       In this -exec rendering, each opcode is executed in the order shown.
       The add opcode, marked with '*', is discussed in more detail.

       The 1st column is the op's sequence number, starting at 1, and is
       displayed in base 36 by default.	 Here they're purely linear; the
       sequences are very helpful when looking at code with loops and
       branches.

       The symbol between angle brackets indicates the op's type, for example;
       <2> is a BINOP, <@> a LISTOP, and <#> is a PADOP, which is used in
       threaded perls. (see "OP class abbreviations").

       The opname, as in 'add[t1]', may be followed by op-specific information
       in parentheses or brackets (ex '[t1]').

       The op-flags (ex 'sK/2') are described in ("OP flags abbreviations").

	   % 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

       The default rendering is top-down, so they're not in execution order.
       This form reflects the way the stack is used to parse and evaluate
       expressions; the add operates on the two terms below it in the tree.

       Nullops appear as "ex-opname", where opname is an op that has been
       optimized away by perl.	They're displayed with a sequence-number of
       '-', because they are not executed (they don't appear in previous
       example), they're printed here because they reflect the parse.

       The arrow points to the sequence number of the next op; they're not
       displayed in -exec mode, for obvious reasons.

       Note that because this rendering was done on a non-threaded perl, the
       PADOPs in the previous examples are now SVOPs, and some (but not all)
       of the square brackets have been replaced by round ones.	 This is a
       subtle feature to provide some visual distinction between renderings on
       threaded and un-threaded perls.

OPTIONS
       Arguments that don't start with a hyphen are taken to be the names of
       subroutines to render; 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 rendered.	 Passing "BEGIN", "UNITCHECK",
       "CHECK", "INIT", or "END" will cause all of the corresponding special
       blocks to be printed.  Arguments must follow options.

       Options affect how things are rendered (ie printed).  They're presented
       here by their visual effect, 1st being strongest.  They're grouped
       according to how they interrelate; within each group the options are
       mutually exclusive (unless otherwise stated).

   Options for Opcode Ordering
       These options control the 'vertical display' of opcodes.	 The display
       'order' is also called 'mode' elsewhere in this document.

       -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, and the '->' at the end of the line
	   indicates the next opcode in execution order.  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).

   Options for Line-Style
       These options select the line-style (or just style) used to render each
       opcode, and dictates what info is actually printed into each line.

       -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 reminiscent 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 reminiscent 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".

   Options for tree-specific formatting
       -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.

       These are pairwise exclusive, i.e. compact or loose, vt or ascii.

   Options controlling sequence numbering
       -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 sequence numbers with the least significant digit first.
	   This is obviously mutually exclusive with bigendian.

   Other options
       -src
	   With this option, the rendering of each statement (starting with
	   the nextstate OP) will be preceded by the 1st line of source code
	   that generates it.  For example:

	       1  <0> enter
	       # 1: my $i;
	       2  <;> nextstate(main 1 junk.pl:1) v:{
	       3  <0> padsv[$i:1,10] vM/LVINTRO
	       # 3: for $i (0..9) {
	       4  <;> nextstate(main 3 junk.pl:3) v:{
	       5  <0> pushmark s
	       6  <$> const[IV 0] s
	       7  <$> const[IV 9] s
	       8  <{> enteriter(next->j last->m redo->9)[$i:1,10] lKS
	       k  <0> iter s
	       l  <|> and(other->9) vK/1
	       # 4:	print "line ";
	       9      <;> nextstate(main 2 junk.pl:4) v
	       a      <0> pushmark s
	       b      <$> const[PV "line "] s
	       c      <@> print vK
	       # 5:	print "$i\n";
	       ...

       -stash="somepackage"
	   With this, "somepackage" will be required, then the stash is
	   inspected, and each function is rendered.

       The following options are pairwise exclusive.

       -main
	   Include the main program in the output, even if subroutines were
	   also specified.  This rendering is normally suppressed when a
	   subroutine name or reference is given.

       -nomain
	   This restores the default behavior after you've changed it with
	   '-main' (it's not normally needed).	If no subroutine name/ref is
	   given, main is rendered, regardless of this flag.

       -nobanner
	   Renderings usually include a banner line identifying the function
	   name or stringified subref.	This suppresses the printing of the
	   banner.

	   TBC: Remove the stringified coderef; while it provides a 'cookie'
	   for each function rendered, the cookies used should be 1,2,3.. not
	   a random hex-address.  It also complicates string comparison of two
	   different trees.

       -banner
	   restores default banner behavior.

       -banneris => subref
	   TBC: a hookpoint (and an option to set it) for a user-supplied
	   function to produce a banner appropriate for users needs.  It's not
	   ideal, because the rendering-state variables, which are a natural
	   candidate for use in concise.t, are unavailable to the user.

   Option Stickiness
       If you invoke Concise more than once in a program, you should know that
       the options are 'sticky'.  This means that the options you provide in
       the first call will be remembered for the 2nd call, unless you re-
       specify or change them.

ABBREVIATIONS
       The concise style uses symbols to convey maximum info with minimal
       clutter (like hex addresses).  With just a little practice, you can
       start to see the flowers, not just the branches, in the trees.

   OP class abbreviations
       These symbols appear before the op-name, and indicate the B:: namespace
       that represents the ops in your Perl code.

	   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

   OP flags abbreviations
       OP flags are either public or private.  The public flags alter the
       behavior of each opcode in consistent ways, and are represented by 0 or
       more single characters.

	   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)
				   Want is unknown
	   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)

       Private flags, if any are set for an opcode, are displayed after a '/'

	   8  <@> leave[1 ref] vKP/REFC ->(end)
	   7	 <2> sassign vKS/2 ->8

       They're opcode specific, and occur less often than the public ones, so
       they're represented by short mnemonics instead of single-chars; see
       op.h for gory details, or try this quick 2-liner:

	 $> perl -MB::Concise -de 1
	 DB<1> |x \%B::Concise::priv

FORMATTING SPECIFICATIONS
       For each line-style ('concise', 'terse', 'linenoise', etc.) there are 3
       format-specs which control how OPs are rendered.

       The first is the 'default' format, which is used in both basic and exec
       modes to print all opcodes.  The 2nd, goto-format, is used in exec mode
       when branches are encountered.  They're not real opcodes, and are
       inserted to look like a closing curly brace.  The tree-format is tree
       specific.

       When a line is rendered, the correct format-spec is copied and scanned
       for the following items; data is substituted in, and other
       manipulations like basic indenting are done, for each opcode rendered.

       There are 3 kinds of items that may be populated; special patterns,
       #vars, and literal text, which is copied verbatim.  (Yes, it's a set of
       s///g steps.)

   Special Patterns
       These items are the primitives used to perform indenting, and to select
       text from amongst alternatives.

       (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.

       ~   Any number of tildes and surrounding whitespace will be collapsed
	   to a single space.

   # Variables
       These #vars represent opcode properties that you may want as part of
       your rendering.	The '#' is intended as a private sigil; a #var's value
       is interpolated into the style-line, much like "read $this".

       These vars take 3 forms:

       #var
	   A property named 'var' is assumed to exist for the opcodes, and is
	   interpolated into the rendering.

       #varN
	   Generates the value of var, left justified to fill N spaces.	 Note
	   that this means while you can have properties 'foo' and 'foo2', you
	   cannot render 'foo2', but you could with 'foo2a'.  You would be
	   wise not to rely on this behavior going forward ;-)

       #Var
	   This ucfirst form of #var generates a tag-value form of itself for
	   display; it converts '#Var' into a 'Var => #var' style, which is
	   then handled as described above.  (Imp-note: #Vars cannot be used
	   for conditional-fills, because the => #var transform is done after
	   the check for #Var's value).

       The following variables are 'defined' by B::Concise; when they are used
       in a style, their respective values are plugged into the rendering of
       each opcode.

       Only some of these are used by the standard styles, the others are
       provided for you to delve into optree mechanics, should you wish to add
       a new style (see "add_style" below) that uses them.  You can also add
       new ones using "add_callback".

       #addr
	   The address of the OP, in hexadecimal.

       #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
	   parentheses.

       #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 hexadecimal.

       #flags
	   The OP's flags, abbreviated as a series of symbols.

       #flagval
	   The numeric value of the OP's flags.

       #hints
	   The COP's hint flags, rendered with abbreviated names if possible.
	   An empty string if this is not a COP. Here are the symbols used:

	       $ strict refs
	       & strict subs
	       * strict vars
	      x$ explicit use/no strict refs
	      x& explicit use/no strict subs
	      x* explicit use/no strict vars
	       i integers
	       l locale
	       b bytes
	       { block scope
	       % localise %^H
	       < open in
	       > open out
	       I overload int
	       F overload float
	       B overload binary
	       S overload string
	       R overload re
	       T taint
	       E eval
	       X filetest access
	       U utf-8

       #hintsval
	   The numeric value of the COP's hint flags, or an empty string if
	   this is not a COP.

       #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 hexadecimal.

       #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 hexadecimal.

       #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 a sequence number
	   generated by B::Concise.

       #seqnum
	   5.8.x and earlier only. 5.9 and later do not provide this.

	   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).

       #opt
	   Whether or not the op has been optimised by the peephole optimiser.

	   Only available in 5.9 and later.

       #sibaddr
	   The address of the OP's next youngest sibling, in hexadecimal.

       #svaddr
	   The address of the OP's SV, if it has an SV, in hexadecimal.

       #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.

One-Liner Command tips
       perl -MO=Concise,bar foo.pl
	   Renders only bar() from foo.pl.  To see main, drop the ',bar'.  To
	   see both, add ',-main'

       perl -MDigest::MD5=md5 -MO=Concise,md5 -e1
	   Identifies md5 as an XS function.  The export is needed so that BC
	   can find it in main.

       perl -MPOSIX -MO=Concise,_POSIX_ARG_MAX -e1
	   Identifies _POSIX_ARG_MAX as a constant sub, optimized to an IV.
	   Although POSIX isn't entirely consistent across platforms, this is
	   likely to be present in virtually all of them.

       perl -MPOSIX -MO=Concise,a -e 'print _POSIX_SAVED_IDS'
	   This renders a print statement, which includes a call to the
	   function.  It's identical to rendering a file with a use call and
	   that single statement, except for the filename which appears in the
	   nextstate ops.

       perl -MPOSIX -MO=Concise,a -e 'sub a{_POSIX_SAVED_IDS}'
	   This is very similar to previous, only the first two ops differ.
	   This subroutine rendering is more representative, insofar as a
	   single main program will have many subs.

       perl -MB::Concise -e 'B::Concise::compile("-exec","-src",
       \%B::Concise::)->()'
	   This renders all functions in the B::Concise package with the
	   source lines.  It eschews the O framework so that the stashref can
	   be passed directly to B::Concise::compile().	 See -stash option for
	   a more convenient way to render a package.

Using B::Concise outside of the O framework
       The common (and original) usage of B::Concise was for command-line
       renderings of simple code, as given in EXAMPLE.	But you can also use
       B::Concise from your code, and call compile() directly, and repeatedly.
       By doing so, you can avoid the compile-time only operation of O.pm, and
       even use the debugger to step through B::Concise::compile() itself.

       Once you're doing this, you may alter Concise output by adding new
       rendering styles, and by optionally adding callback routines which
       populate new variables, if such were referenced from those (just added)
       styles.

   Example: Altering Concise Renderings
	   use B::Concise qw(set_style add_callback);
	   add_style($yourStyleName => $defaultfmt, $gotofmt, $treefmt);
	   add_callback
	     ( sub {
		   my ($h, $op, $format, $level, $stylename) = @_;
		   $h->{variable} = some_func($op);
	       });
	   $walker = B::Concise::compile(@options,@subnames,@subrefs);
	   $walker->();

   set_style()
       set_style accepts 3 arguments, and updates the three format-specs
       comprising a line-style (basic-exec, goto, tree).  It has one minor
       drawback though; it doesn't register the style under a new name.	 This
       can become an issue if you render more than once and switch styles.
       Thus you may prefer to use add_style() and/or set_style_standard()
       instead.

   set_style_standard($name)
       This restores one of the standard line-styles: "terse", "concise",
       "linenoise", "debug", "env", into effect.  It also accepts style names
       previously defined with add_style().

   add_style ()
       This subroutine accepts a new style name and three style arguments as
       above, and creates, registers, and selects the newly named style.  It
       is an error to re-add a style; call set_style_standard() to switch
       between several styles.

   add_callback ()
       If your newly minted styles refer to any new #variables, you'll need to
       define a callback subroutine that will populate (or modify) those
       variables.  They are then available for use in the style you've chosen.

       The callbacks are called for each opcode visited by Concise, in the
       same order as they are added.  Each subroutine is passed five
       parameters.

	 1. A hashref, containing the variable names and values which are
	    populated into the report-line for the op
	 2. the op, as a B<B::OP> object
	 3. a reference to the format string
	 4. the formatting (indent) level
	 5. the selected stylename

       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.

   Running B::Concise::compile()
       compile accepts options as described above in "OPTIONS", and arguments,
       which are either coderefs, or subroutine names.

       It constructs and returns a $treewalker coderef, which when invoked,
       traverses, or walks, and renders the optrees of the given arguments to
       STDOUT.	You can reuse this, and can change the rendering style used
       each time; thereafter the coderef renders in the new style.

       walk_output lets you change the print destination from STDOUT to
       another open filehandle, or into a string passed as a ref (unless
       you've built perl with -Uuseperlio).

	   my $walker = B::Concise::compile('-terse','aFuncName', \&aSubRef);  # 1
	   walk_output(\my $buf);
	   $walker->();			       # 1 renders -terse
	   set_style_standard('concise');      # 2
	   $walker->();			       # 2 renders -concise
	   $walker->(@new);		       # 3 renders whatever
	   print "3 different renderings: terse, concise, and @new: $buf\n";

       When $walker is called, it traverses the subroutines supplied when it
       was created, and renders them using the current style.  You can change
       the style afterwards in several different ways:

	 1. call C<compile>, altering style or mode/order
	 2. call C<set_style_standard>
	 3. call $walker, passing @new options

       Passing new options to the $walker is the easiest way to change amongst
       any pre-defined styles (the ones you add are automatically recognized
       as options), and is the only way to alter rendering order without
       calling compile again.  Note however that rendering state is still
       shared amongst multiple $walker objects, so they must still be used in
       a coordinated manner.

   B::Concise::reset_sequence()
       This function (not exported) lets you reset the sequence numbers (note
       that they're numbered arbitrarily, their goal being to be human
       readable).  Its purpose is mostly to support testing, i.e. to compare
       the concise output from two identical anonymous subroutines (but
       different instances).  Without the reset, B::Concise, seeing that
       they're separate optrees, generates different sequence numbers in the
       output.

   Errors
       Errors in rendering (non-existent function-name, non-existent coderef)
       are written to the STDOUT, or wherever you've set it via walk_output().

       Errors using the various *style* calls, and bad args to walk_output(),
       result in die().	 Use an eval if you wish to catch these errors and
       continue processing.

AUTHOR
       Stephen McCamant, <smcc@CSUA.Berkeley.EDU>.

perl v5.16.2			  2012-10-25		       B::Concise(3pm)
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Polarhome, production since 1999.
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Based on Fawad Halim's script.
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