README.txt

		________________________________________

		 P2X - UNIVERSAL PARSER WITH XML OUTPUT

			   Johannes Willkomm
		________________________________________


Table of Contents
_________________

1 Introduction
2 Usage
.. 2.1 Program Configuration
..... 2.1.1 Options
..... 2.1.2 Configuration file
..... 2.1.3 Environment variables
.. 2.2 Language definition
..... 2.2.1 Class Item
..... 2.2.2 Class Binary
..... 2.2.3 Class Unary
..... 2.2.4 Class Unary_Binary
..... 2.2.5 Class Postfix
..... 2.2.6 Class Ignore
..... 2.2.7 Parentheses
..... 2.2.8 Line comments and block comments
..... 2.2.9 Ignoring tokens depending on context
..... 2.2.10 Example
3 About this document





1 Introduction
==============

  P2X is a parser, configurable by shortcut grammars, with XML
  output. The parser uses recursive descent parsing to read any kind of
  text such as program code, configuration files or even natural
  language. The input is structured as a tree according to grammar rules
  which can be specified in a very concise and simple form. The XML
  output is in a form that makes unparsing particularly simple. This
  makes P2X suitable for the integration of non-XML data into XML-based
  projects and/or for source transformation using XSLT.

  Consider the following example, were we define solely the binary
  operator PLUS and specify XML output in /merged mode/:
  ,----
  | echo -n "1+2+3" > in.txt
  | p2x -m -X -b PLUS -o out.xml in.txt
  | cat out.xml
  `----

  ,----
  | <?xml version="1.0" encoding="utf-8"?>
  | <!-- P2X version 0.6.4 (72b96eb2) -->
  | <code-xml xmlns='http://johannes-willkomm.de/xml/code-xml/' xmlns:c='http://johannes-willkomm.de/xml/code-xml/attributes/' xmlns:ci='http://johannes-willkomm.de/xml/code-xml/ignore'>
  |  <ROOT>
  |   <null/>
  |   <PLUS>
  |    <INT><c:t>1</c:t></INT>
  |    <c:t>+</c:t>
  |    <INT><c:t>2</c:t></INT>
  |    <c:t>+</c:t>
  |    <INT><c:t>3</c:t></INT>
  |   </PLUS>
  |  </ROOT>
  | </code-xml>
  `----

  One important property of the output is that all input token are
  present, and that they are present strictly in the order of the
  input. Thus the entire input text is present in the XML, structured by
  XML tags. This is even true when some token are set to be ignored. The
  ignored token are inserted into the tree by attaching them to the next
  best tree node, but otherwise they have no effect on the shape of the
  tree.

  ,----
  | echo -n "1 + 2 + 3" > in.txt
  | p2x -m -X -i SPACE -b PLUS -o out.xml in.txt
  | cat out.xml
  `----

  ,----
  | <?xml version="1.0" encoding="utf-8"?>
  | <!-- P2X version 0.6.4 (72b96eb2) -->
  | <code-xml xmlns='http://johannes-willkomm.de/xml/code-xml/' xmlns:c='http://johannes-willkomm.de/xml/code-xml/attributes/' xmlns:ci='http://johannes-willkomm.de/xml/code-xml/ignore'>
  |  <ROOT>
  |   <null/>
  |   <PLUS>
  |    <INT>
  |     <c:t>1</c:t>
  |     <ci:SPACE> </ci:SPACE>
  |    </INT>
  |    <c:t>+</c:t>
  |    <ci:SPACE> </ci:SPACE>
  |    <INT>
  |     <c:t>2</c:t>
  |     <ci:SPACE> </ci:SPACE>
  |    </INT>
  |    <c:t>+</c:t>
  |    <ci:SPACE> </ci:SPACE>
  |    <INT><c:t>3</c:t></INT>
  |   </PLUS>
  |  </ROOT>
  | </code-xml>
  `----

  Any token in the tree has exactly one special child element that
  contains the input token text, in the example called `c:t'. Ignored
  token are output as elements with namespace prefix `ci', in the
  example called `ci:SPACE'.

  Since the token text and ignored elements are in separate namespaces,
  they do not affect the structure of the tree made up of the elements
  of the code namespace. Still, the input can be recovered exactly by
  concatenating the token text and ignored elements in document
  order. This is done for example by the XSL stylesheet
  [file:src/xsl/reproduce.xsl]:

  ,----
  | xsltproc src/xsl/reproduce.xsl out.xml
  `----

  ,----
  | 1 + 2 + 3
  `----

  The parsed tree structure can also be represented in MATLAB output:
  ,----
  | p2x -M -i SPACE -b PLUS in.txt
  `----

  ,----
  | struct('n','rt','i','','c',{...
  |  struct('n',{'','op'}, 't',{'','+'}, 'i',{'',' '}, 'c',{[],...
  |   struct('n',{'op','num'}, 't',{'+','3'}, 'i',{' ',''}, 'c',{...
  |    struct('n','num', 't',{'1','2'}, 'i',' '),[]})})});
  `----

  or JSON:
  ,----
  | p2x -J -i SPACE -b PLUS in.txt
  `----

  ,----
  | {"n":"rt","i":"","c":[
  |  {"n":["","op"], "t":["","+"], "i":[""," "], "c":[{},
  |   {"n":["op","num"], "t":["+","3"], "i":[" ",""], "c":[
  |    {"n":"num", "t":["1","2"], "i":" "},{}]}]}]}
  `----

  In both MATLAB and JSON format it is not possible to represent all
  ignored items when using the merged output mode.


2 Usage
=======

  P2X works as a stream filter, it reads from standard input and writes
  to standard output. For example, to read input from file `in.txt' and
  write the XML file `out.xml', invoke P2X as follows
  ,----
  | p2x < in.txt > out.xml
  `----
  P2X can also read from a file given as the first command line argument
  ,----
  | p2x in.txt > out.xml
  `----
  or write its output to a file given by command line option `-o'
  ,----
  | p2x in.txt -o out.xml
  `----

  There are currently four different output modes:

  - with option `-X' or `--xml' the tree is output in XML format
  - with option `-M' or `--matlab' the tree is output in MATLAB format,
    as a single large `struct' expression
  - with option `-J' or `--json' the tree is output in JSON format
  - the default is to output an older version of the XML format, which
    is more verbose

  In XML the output tree is as described in this document. In MATLAB and
  JSON each node has the three fields `n', `t' and `c', for the node
  name, the node text and the node children, respectively.


2.1 Program Configuration
~~~~~~~~~~~~~~~~~~~~~~~~~

  P2X can be configured either by options on the command line or from a
  configuration file, usually `$HOME/.p2x/p2x-options'.


2.1.1 Options
-------------



  Each option has a long name and some also have a short name. The most
  important options are the following:

  -o, --output
        specify name of output file
  -p, --prec-list
        specify name of language definition file
  -m, --merged
        set merged output mode
  -X, -M, or -J
        set XML, MATLAB, or JSON output mode
  -S
        specify scanner (lexer)
  -g
        add debug information such as line numbers

  The configuration options are listed in entirety in the following
  table:

   Short  Long Option               Description                                                                                 
  ------------------------------------------------------------------------------------------------------------------------------
   -h     --help                    Print help and exit                                                                         
          --full-help               Print help, including hidden options, and exit                                              
          --version                 Print version and exit                                                                      
   -V     --verbose=<number>        Control messages by bit mask (default=`error,warning')                                      
          --debug                   Enable debugging  (default=off)                                                             
   -p     --prec-list=filename      Precedence file list                                                                        
   -i     --ignore=TokenList        Add an item to ignore                                                                       
   -b     --binary=TokenList        Add a binary operator                                                                       
   -r     --right=TokenList         Add a right associative operator                                                            
   -u     --unary=TokenList         Add a unary operator                                                                        
          --postfix=TokenList       Add a postfix operator                                                                      
   -I     --item=TokenList          Add an item                                                                                 
   -B     --brace=TokenPair         Scope start and end token                                                                   
   -L     --list-token              List token types  (default=off)                                                             
   -T     --list-classes            List token classes  (default=off)                                                           
   -s     --scan-only               Scan only, do not parse  (default=off)                                                      
   -S     --scanner=name            Select scanner class  (default=`strings')                                                   
   -e     --input-encoding=Charset  Input encoding  (default=`utf-8')                                                           
          --stdin-tty               Read from stdin, even if it is a TTY (default=off)                                          
  ------------------------------------------------------------------------------------------------------------------------------
   -o     --outfile=Filename        Write output to file `Filename'                                                             
          --indent                  Indent  (default=on)                                                                        
          --indent-unit=String      Indentation unit  (default=` ')                                                             
          --newline-as-br           Emit newline text as ca:br element of ca:text (default=on)                                  
          --newline-as-entity       Emit newline text as &#xa; character entity (default=off)                                   
   -m     --merged                  Merge same operator chains, tree will not be binary (default=off)                           
   -n     --noignore                Skip ignored token  (default=off)                                                           
   -l     --loose                   Write null elements more loosely (default=off)                                              
          --strict                  Write null elements more strictly (default=off)                                             
   -O     --output-mode=Mode        Write output as normal (x) or alternative (y) XML, or (J)SON or (M)ATLAB code (default=`y') 
   -M     --matlab                  Write output as MATLAB  (default=off)                                                       
   -J     --json                    Write output as JSON  (default=off)                                                         
   -X     --xml                     Write output as XML  (default=off)                                                          
          --write-recursive         Recursive output writing  (default=off)                                                     
   -g     --src-info                Emit source location attributes line, column, and character  (default=off)                  
          --attribute-line          Emit attribute line with source line (default=on)                                           
          --attribute-column        Emit attribute column with source column (default=on)                                       
          --attribute-char          Emit attribute column with source char (default=off)                                        
          --attribute-precedence    Emit attribute precedence with token precedence (default=off)                               
          --attribute-mode          Emit attribute mode with token mode (default=off)                                           
          --attribute-type          Emit attribute type with token type (default=on)                                            
          --attribute-id            Emit attribute id with token id  (default=off)                                              


2.1.2 Configuration file
------------------------

  The same options (see previous Section 2.1.1) as on the command line
  can also be given in a configuration file, which by default searched
  as `~/.p2x/p2x-options'. In that file there may be one option per
  line, short or long, but without the leading `-' or `--'. For example,
  the following three lines all enable the verbosity level `debug':

  ,----
  | V debug
  | verbose debug
  | verbose=debug
  `----

  See also environment variable P2X_USER_DIR in Section [Environment
  variables].


[Environment variables] See figure (2 1 3)


2.1.3 Environment variables
---------------------------



  - HOME: Linux only: determine home directory of current user

  - HOMEDRIVE, HOMEPATH, APPDATA: Windows only: determine home directory
    of current user

  - P2X_USER_DIR: Set the directory where the configuration file
    `p2x-options' is found. Default is $HOME/.p2x

  - P2X_CONFIG_DIR: If set, this directory is also searched for language
    definition files

  - P2X_DEBUG_INIT: set to non-empty string to turn on debugging of the
    initialization of P2X


2.2 Language definition
~~~~~~~~~~~~~~~~~~~~~~~

  The equivalent of a grammar is called language definition in P2X. It
  consists of an assignment of /token/ to /token classes/. Token are
  those listed by the option `--list-token' or `-L'.

  Which token are returned for a given character input depends on the
  scanner selected with option `--scanner' or `-S'. Since the scanners
  are defined with Flex there currently is only limited set of scanners
  to chose from: `c', `r', `strings', `no-strings'. For example, the
  `no-strings' scanner reports each single quote `'' as a token APOS and
  each double quote `"' character as a token QUOTE, and it will never
  return a token STRING.

  The available token classes are the following:

  - Item
  - Binary
  - Unary
  - Binary_unary
  - Postfix
  - Ignore
  - Line_comment
  - Block_comment

  Identifiers play a special role, that is, while IDENTIFIER is listed
  as one of the token types, each identifier such as `x', `sin' or
  `times' may individually be assigned to a token class. For example
  `sin' might be assigned to class Unary and `times' might be assigned
  to class Binary. The set of legal identifiers also depends on the
  selected scanner, but as of now all scanners have the same definition.

  The basic definition of an identifier is based on the C
  model. Identifiers may also contain any of the upper Unicode
  characters. Currently the hyphen character may not occur in an
  identifier, for example, "a-b" will be scanned as three tokens.

  The token ROOT and JUXTA are special: ROOT is always in class Unary
  with precedence 0 and JUXTA is always in class Binary, and the
  precedence and associativity of this operator may be set by the
  user. Both ROOT and JUXTA do not represent any input. The ROOT token
  is always present as the root of the parse tree. The JUXTA token is
  automatically inserted in the parse tree as a binary operator whenever
  two consecutive items are encountered.

  By default all other token are in class Item.

  Also, a pair of token may be declared as /parentheses/. This pair of
  token encapsulates some subexpression and will be inserted into the
  parse tree as a whole. The content of a parentheses is itself a parse
  tree.

  A parentheses element can also be assigned to a token class. For
  example, the parentheses `(' and `)' may be declared as a postfix
  operator.

  The effect of the configuration can be inspected by using the option
  `-T'.
  ,----
  | p2x -T -p examples/configs-special/cfuncs.p2c
  `----

  Generally token can either by referred to by the name of the token
  class as listed by the option `-L' or they can be referred to
  literally, in quotes. For example, the following two lines are
  equivalent:

  ,----
  | MULT    binary 1002
  | "*"     binary 1002
  `----

  Currently there is no way to see the regular expression used by the
  scanner for each token type, and no way to see which set of input
  words is represented by a given token. Also there is currently no
  documentation telling you that the token returned by the scanner for
  the input `*' is called MULT. Hence it is probably preferably to use
  the second form. For individual identifiers the only option is of
  course to use the quoted form.

  Example configuration files can be found in the directory
  `examples/configs'. The file [./examples/configs/default] is used by
  the P2X test suite and showcases all available declarations and
  options.


2.2.1 Class Item
----------------

  All token types, except JUXTA and ROOT, are by default in class
  Item. Items are represented as tree nodes without children, also
  called leafs. Two consecutive items are joined automatically by
  artificial binary JUXTA nodes.


2.2.2 Class Binary
------------------

  Token types in class Binary represent binary operators, which become
  binary nodes in the tree, that is, they will usually have two
  children. A Binary token type has the associated fields /associativiy/
  and /precedence/.

  The class Binary is typically used for mathematical binary operators
  such as +, -, *, / etc. One might also declare identifiers such as
  `and' or `or' as Binary. Binary token play a crucial role in
  structuring the tree. For example, to parse a text file into the
  individual lines, put token NEWLINE in class Binary, presumably with a
  rather low precedence.

  A token from class Binary has a /precedence/, which is a positive
  integer, to order the binding strength of two adjacent operators. The
  typical case is plus + and multiply *, where * has the higher
  precedence. This way a+b*c is the same as a+(b*c) and a*b+c is the
  same as (a*b)+c.

  A token from class Binary also has an /associativity/ which is either
  /left/ or /right/ to order two adjacent operators of the same
  precedence. Usually, arithmetic operators like + and * are
  left-associative, which means that a*b*c is the same as (a*b)*c. An
  example for a right-associative operator is the assignment = in C,
  where x=y=z is the same as x=(y=z).

  A token is added to class Binary by one of two ways: first, by using
  the option `-b' or `--binary', where you can use token names or
  identifiers. The token will be given increasing precedences in the
  order they appear in the command line, from the left to the right,
  beginning with 1000:
  ,----
  | p2x -b NEWLINE -b PLUS -bMULT,DIV -btimes,divide
  `----

  The other way is by a `binary' declaration in the laguage definition
  file, which has the form `token' `binary' followed by one to four
  further fields: two integer precedences, an associativity (`left' or
  `right') and an output mode (`nested' or `merged').
  ,----
  | newline binary 1000 merged
  | "="     binary 1001 right nested
  | "*"     binary 1002 merged left
  `----

  In the output tree the binary operators are represented as binary
  nodes with two children, their left and right operands. This can lead
  to deeply nested trees. To mitigate this P2X can also output the
  binary nodes in /merged/ mode. Then $n$ consecutive operators made of
  the same token are collapsed into a single node with $n+1$
  children. The option `-m' or `--merged' activates the merged output
  globally and the `merged' keyword in a language definition declaration
  can activate merged mode for individual operators in class Binary.


2.2.3 Class Unary
-----------------

  Token types in class Unary represent unary prefix operators, which
  become unary nodes in the tree, that is, they will at most have a
  single child. The child will always be the right child, that is, the
  left pointer is always null. A Unary token type has the associated
  field /precedence/.

  The class Unary is typically used for mathematical unary operators
  such as +, -. One might also declare identifiers such as `sin' or
  `cos' as Unary. Another use might be for a line comment delimiter such
  as `#'.

  A token is added to class Unary by one of two ways: first, by using
  the option `-u' or `--unary', where you can use token names or
  identifiers. The token will be given increasing precedences in the
  order they appear in the command line, from the left to the right,
  beginning with 2000:
  ,----
  | p2x  -u 'sin,cos'
  `----

  The other way is by a `unary' declaration in the laguage definition
  file, which has the form `token' `unary' followed by an integer
  precedence field. The command line settings above are equivalent to
  the following entries in the language definition file:
  ,----
  | "sin" unary 2000
  | "cos" unary 2001
  `----

  In the output tree Unary operators are output as a node with a two
  child nodes, as they can be seen as a binary operator with the left
  operand missing. The missing left operand is marked with a special
  `null' element, so that the single operand is the second child
  element.


2.2.4 Class Unary_Binary
------------------------

  Class Unary_Binary is for token which may either occur as unary
  operators or as binary operators. A typical example are plus `+' and
  minus `-' in mathematical notation. For that, token may be assigned to
  class Unary_Binary, which accepts two integer options, the first of
  which is the binary precedence and the second the unary precedence. An
  associativity may also be specified. For example, the following
  configuration
  ,----
  | "-" unary_binary 1000 2200 left
  `----

  The same input `-3' can now result in either a unary node or a binary
  node in the output tree, depending on the preceding token. When an
  Item is pending because the preceding token was of class Unary or
  Binary the minus `-' will result in a unary operator node, otherwise
  as a binary node.


2.2.5 Class Postfix
-------------------

  The class Postfix is complementary of the Unary class. It defines a
  unary postfix operator. Typical examples are the operators `'' and
  `.'' in MATLAB. Another example would be to define units as postfix
  operators:

  ,----
  | "kg" postfix 10000
  | "m" postfix 10000
  | "s" postfix 10000
  `----

  Another important application are the typical function call and array
  access expressions in may languages, such as `f(x)' or `x[2]'. These
  are most conveniently treated as postfix operators, which is possible
  with P2X because each pair of parentheses can also be given a token
  class, see section 2.2.7.

  ,----
  | "(" PAREN ")" postfix 10000
  | "[" PAREN "]"  postfix 10000
  `----

  In the output tree Postfix operators are output as a node with a
  single child, as they can be seen as a binary operator with the right
  operand missing.


2.2.6 Class Ignore
------------------

  A token in class Ignore is not used in the construction of the parse
  tree. However it is not simply discarded. Instead, it is inserted into
  the tree at the next best convenient location. Thus the text that
  constituted it is not lost but may be found in the tree as a sort of
  side information.

  In the language definition file, a token is assigned to class Ignore
  with the keyword `ignore', but a precedence is also required (it is
  ignored):
  ,----
  | NEWLINE ignore 1
  `----

  In the XML output token in class Ignore are represented using a
  separate namespace, so for many intents and purposes they are as good
  as invisible. However, for input reconstruction it is of course
  crucial that they are kept.

  Keeping the Ignore token one can reconstruct input identically even if
  its structure is unknown. P2X guarantees that all input characters,
  including those from token in class Ignore also occur in the output
  XML document, in the same order as they occured in the input.

  In the MATLAB and JSON output formats it is not possible to represent
  the token in class Ignore, so they are truly ignored and discared
  then.


2.2.7 Parentheses
-----------------



  A pair of token which is declared as Parentheses encapsulates a
  subexpression, such that on the outside it appears as a single item,
  and in fact it is handled by default in the same way as a token from
  class Item. A Parenthesis definition has a /closing list/, which is a
  list of token that may close the subexpression. For example, one could
  declare the left parenthesis token `(' and the right parenthesis `)'
  as being a Parenthesis. For each opening token, the Parenthesis
  declarations are merged together, merging the closing lists. For
  example, one might declare `while' and `end' and `while' and
  `endwhile' as Parentheses, then there will be internally just one
  Parenthesis definition for `while' with the closing list set to the
  tupel (`end', `endwhile').

  A token may be added to class Parentheses using the command line
  option `-B' or `--brace', which requires as an argument a pair of
  token separated by `,' or `:'., for example like this:
  ,----
  | p2x -B '(:)' -B 'while:end' -B 'while:endwhile' -
  `----
  or using a `paren' declaration in the language definition file:
  ,----
  | "(" paren ")"
  | "while" paren "end"
  | "while" paren "endwhile"
  `----

  A parenthesis expression is be default handled as being in token class
  Item. However, parentheses declarations may also be assigned to any
  other token class. This can be done for each parentheses declaration
  individually. For example, the parentheses `(' and `)' may be declared
  as being a postfix operator, to represent the typical function call
  expression like `f(x)'. This is done by adding the class keyword on
  the line together with an integer specifying the precedence:
  ,----
  | "(" paren ")" postfix 10000
  `----

  Another way to parse a function call expression is to leave the
  parentheses definition in token class Item and rely on the JUXTA
  operator which will be inserted between the function name -- provided
  that is parsed as an Item -- and the parentheses. One will probably
  give a rather high precedence to the JUXTA operator then.

  ,----
  | "(" paren ")"
  | JUXTA binary 2000
  `----


2.2.8 Line comments and block comments
--------------------------------------

  Line comments and block comments can be used to escape from the normal
  parsing parse comment text sections. Line comments start with a
  certain token and continue until the next NEWLINE token. Block
  comments work like parentheses and have start and end tokens.

  All the text belonging to a comment is collected and inserted as a
  single Ignore item into the parse tree. In the case of the line
  comment the terminating NEWLINE is inserted individually, according to
  the rules defined for it.

  For example, the two modes of comments used in the C++ language can be
  configured in P2X as follows:

  ,----
  | "//" line_comment 1
  | "/*" block_comment "*/"
  `----


2.2.9 Ignoring tokens depending on context
------------------------------------------

  There are two special rules that can override the normally configured
  mode for certain token classes depending on the context. The first is
  the flag `ignoreIfStray' that can be used with Binary token. The
  effect is that a token from that class is treated as an Ignore token
  when there is an open operator (Unary or Binary) in the tree already.

  The other special rule is `A ignoreAfter B', which means that a token
  A is treated as Ignore whenever it occurs after a B token.

  For example, a special token to escape a NEWLINE, as in MATLAB, can be
  configured in P2X as follows:

  ,----
  | NEWLINE    BINARY 1000
  | "..."      IGNORE 1
  | NEWLINE    ignoreAfter "..."
  `----


2.2.10 Example
--------------

  As an example consider the configuration file
  [file:examples/configs-special/cfuncs.p2c] and the input text file
  [file:examples/in/cexpr.exp]:
  ,----
  | cat examples/configs-special/cfuncs.p2c
  `----

  ,----
  | #
  | # Operator definitions
  | #
  | # Token  Class         Precedence  Unary Prec.  Associativity  Options
  | ","      binary        3                                       merged
  | ";"      binary        3                                       merged
  | "return" unary         4
  | JUXTA    binary        5
  | "="      binary        6                        right
  | "=="     binary        7
  | 
  | "+"      unary_binary  10          110
  | "-"      unary_binary  10          110
  | 
  | "*"      unary_binary  20          120
  | 
  | "/"      binary        30
  | "%"      binary        30
  | 
  | "if"     unary        100
  | "while"  unary        100
  | 
  | #
  | # Parentheses definitions
  | #
  | # Start  "paren" End  Class    Precedence  Unary Prec.  Associativity
  | "("      paren   ")"  postfix  101
  | "["      paren   "]"  postfix  102
  | "{"      paren   "}"
  | 
  | " "      ignore        1
  | NEWLINE  ignore        1
  | TAB      ignore        1
  `----

  ,----
  | cat examples/in/cexpr.exp
  `----

  ,----
  | f( a +	1)*2
  `----

  ,----
  | p2x -S c -lnX -p examples/configs-special/cfuncs.p2c examples/in/cexpr.exp
  `----

  ,----
  | <?xml version="1.0" encoding="utf-8"?>
  | <!-- P2X version 0.6.4 (72b96eb2) -->
  | <code-xml xmlns='http://johannes-willkomm.de/xml/code-xml/' xmlns:c='http://johannes-willkomm.de/xml/code-xml/attributes/' xmlns:ci='http://johannes-willkomm.de/xml/code-xml/ignore'>
  |  <ROOT>
  |   <MULT>
  |    <L_PAREN>
  |     <ID><c:t>f</c:t></ID>
  |     <c:t>(</c:t>
  |     <R_PAREN>
  |      <PLUS>
  |       <ID><c:t>a</c:t></ID>
  |       <c:t>+</c:t>
  |       <INT><c:t>1</c:t></INT>
  |      </PLUS>
  |      <c:t>)</c:t>
  |     </R_PAREN>
  |    </L_PAREN>
  |    <c:t>*</c:t>
  |    <INT><c:t>2</c:t></INT>
  |   </MULT>
  |  </ROOT>
  | </code-xml>
  `----

  As a more complex example try parsing an entire program:

  ,----
  | p2x -lnX -S c -p examples/configs-special/cfuncs.p2c examples/in/cfunc.exp
  `----


3 About this document
=====================

  This file is part of P2X. See the file p2x.cc for copying conditions.

  Copyright © 2014,2016,2018 Johannes Willkomm