


ext::B::B::ConcisPerl)Programmers Referenceext::B::B::Concise(3p)


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]').




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       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.



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       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.



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       -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 seqence 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



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           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.



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       -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)




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       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



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           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.





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       #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
               i integers
               l locale
               b bytes
               [ arybase
               { 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.





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       #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.




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       #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.





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       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().




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   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



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       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 v5.10.1                2009-10-12                         14


