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B::Concise(3)          Perl Programmers Reference Guide          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 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 an example of 2 outputs (aka 'renderings'), using the -exec and -basic (i.e. default) formatting conven-
       tions 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

       Each line corresponds to an opcode. The opcode marked with '*' is used in a few examples below.

       The 1st column is the op's sequence number, starting at 1, and is displayed in base 36 by default.  This ren-
       dering is in -exec (i.e.  execution) order.

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

       The op-flags (ex 'sK/2') follow, and 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 fea-
       ture 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 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 rendered.  Passing "BEGIN", "CHECK", "INIT", or "END" will cause all of the corresponding
       special blocks to be printed.

       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 inden-
           tation 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 actu-
       ally 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 repre-
           sented 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 charac-
           ter 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 char-
           acters, 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 cur-
           rently 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.  This is obviously mutually exclusive with
           bigendian.

       Other options

       These are pairwise exclusive.

       -main
           Include the main program in the output, even if subroutines were also specified.  This rendering is nor-
           mally 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 sup-
           presses 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 substi-
       tuted 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 inden-
           tation 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 prop-
           erties '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 condi-
           tional-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.

       #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.

       #static
           Whether or not the op is statically defined.  This flag is used by the B::C compiler backend and indicates
           that the op should not be freed.

           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.

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 EXAM-
       PLE.  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::Con-
       cise::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 subrou-
       tine 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 subrou-
       tine 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 com-
       pile 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, <smccATCSUA.EDU>.



perl v5.8.8                       2001-09-21                     B::Concise(3)