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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 struc-
       ture, and the format of the information displyed is cus-
       tomizable. 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 (aka 'rendering'),
       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 opcode. Null ops appear as
       "ex-opname", where opname is the op that has been opti-
       mized 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,



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       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 spe-
       cial 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 interre-
       late; 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.  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).






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       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 conven-
           tions. 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 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



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           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 cur-
           rently supported. The default is 36.

       -bigendian
           Print sequence numbers with the most significant digit
           first. This is the usual convention for Arabic numer-
           als, and the default.

       -littleendian
           Print seqence numbers with the least significant digit
           first.  This is obviously mutually exclusive with
           bigendian.

       Other options


       -main
           Include the main program in the output, even if sub-
           routines were also specified.  This is the only option
           that is not sticky (see below)

       -banner
           B::Concise::compile normally prints a banner line
           identifying the function name, or in case of a subref,
           a generic message including (unfortunately) the
           stringified coderef.  This option suppresses the
           printing of the banner.

       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.

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



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       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 string is
       scanned for the following items, and data is substituted
       in, or other manipulations, like basic indenting.  Any
       text that doesn't match a special pattern (the items
       below) is copied verbatim.  (Yes, it's a set of s///g
       steps.)

       (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 indenta-
           tion 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), gen-
           erates 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.





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       #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.





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       #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 num-
           ber 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 hex-
           idecimal.

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

       #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





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       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
       You can use B::Concise, and call compile() directly, and
       repeatedly.  By doing so, you can avoid the compile-time
       only operation of 'perl -MO=Concise ..'.  For example, you
       can use the debugger to step through B::Concise::compile()
       itself.

       When doing so, you can alter Concise output by providing
       new output styles, and optionally by adding callback rou-
       tines which populate new variables that may be rendered as
       part of those styles.  For all following sections, please
       review "FORMATTING SPECIFICATIONS".

       Example: Altering Concise Renderings

           use B::Concise qw(set_style add_callback);
           set_style($your_format, $your_gotofmt, $your_treefmt);
           add_callback
             ( sub {
                   my ($h, $op, $format, $level, $stylename) = @_;
                   $h->{variable} = some_func($op);
               }
             );
           B::Concise::compile(@options)->();





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       set_style()

       set_style accepts 3 arguments, and updates the three for-
       mat-specs comprising a line-style (basic-exec, goto,
       tree).  It has one minor drawback though; it doesn't reg-
       ister 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 #variables,
       you'll need to define a callback subroutine that will pop-
       ulate (or modify) those variables.  They are then avail-
       able for use in the style you've chosen.

       The callbacks are called for each opcode visited by Con-
       cise, 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 subroutine
       names.




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       compile() constructs and returns a coderef, which when
       invoked, scans the optree, and prints the results to STD-
       OUT.  Once you have the coderef, you may change the output
       style; 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.

           walk_output(\my $buf);
           my $walker = B::Concise::compile('-concise','funcName', \&aSubRef);
           print "Concise Banner for Functions: $buf\n";
           $walker->();
           print "Concise Rendering(s)?: $buf\n";

       For each subroutine visited by Concise, the $buf will con-
       tain a banner naming the function or coderef about to be
       traversed.  Once $walker is invoked, it prints the actual
       renderings for each.

       To switch back to one of the standard styles like "con-
       cise" or "terse", call "set_style_standard", or pass the
       style name into B::Concise::compile() (as done above).

       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

       All detected errors, (invalid arguments, internal errors,
       etc.) are resolved with a die($message). Use an eval if
       you wish to catch these errors and continue processing.

       In particular, compile will die if you've asked for a non-
       existent function-name, a non-existent coderef, or a non-
       CODE reference.

AUTHOR
       Stephen McCamant, <smccATCSUA.EDU>.










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