btparse::doc::bt_post_processing(3)				      btparse				       btparse::doc::bt_post_processing(3)

NAME

       bt_post_processing - post-processing of BibTeX strings, values, and entries

SYNOPSIS

	  void bt_postprocess_string (char * s,
				      btshort options)

	  char * bt_postprocess_value (AST *   value,
				       btshort	options,
				       boolean replace);

	  char * bt_postprocess_field (AST *   field,
				       btshort	options,
				       boolean replace);

	  void bt_postprocess_entry (AST *  entry,
				     btshort options);

DESCRIPTION

       When btparse parses a BibTeX entry, it initially stores the results in an abstract syntax tree (AST), in a form exactly mirroring the
       parsed data.  For example, the entry

	  @Article{Jones:1997a,
	    AuThOr = "Bob   Jones" # and # "Jim Smith ",
	    TITLE = "Feeding Habits of
		     the Common Cockroach",
	    JoUrNaL = j_ent,
	    YEAR = 1997
	  }

       would parse to an AST that could be represented as follows:

	  (entry,"Article")
	    (key,"Jones:1997a")
	    (field,"AuThOr")
	      (string,"Bob   Jones")
	      (macro,"and")
	      (string,"Jim Smith ")
	    (field,"TITLE")
	      (string,"Feeding Habits of	       the Common Cockroach")
	    (field,"JoUrNaL")
	      (macro,"j_ent")
	    (field,"YEAR")
	      (number,"1997")

       The advantage of this form is that all the important information in the entry is readily available by traversing the tree using the
       functions described in bt_traversal.  This obvious problem is that the data is a little too raw to be immediately useful: entry types and
       field names are inconsistently capitalized, strings are full of unwanted whitespace, field values not reduced to single strings, and so
       forth.

       All of these problems are addressed by btparse's post-processing functions, described here.  Normally, you won't have to call these
       functions---the library does the Right Thing for you after parsing each entry, and you can customize what exactly the Right Thing is for
       your application.  (For instance, you can tell it to expand macros, but not to concatenate substrings together.)  However, it's conceivable
       that you might wish to move the post-processing into your own code and out of the library's control.  More likely, you could have strings
       that come from something other than BibTeX files that you would like to have treated as BibTeX strings; for that situation, the post-
       processing functions are essential.  Finally, you might just be curious about what exactly happens to your data after it's parsed.  If so,
       you've come to the right place for excruciatingly detailed explanations.

FUNCTIONS

       btparse offers four points of entry to its post-processing code.  Of these, probably only the first and last---for processing individual
       strings and whole entries---will be commonly used.

   Post-processing entry points
       To understand why four entry points are offered, an explanation of the sample AST shown above will help.  First of all, the whole entry is
       represented by the "(entry,"Article")" node; this node has the entry key and all its field/value pairs as children.  Entry nodes are
       returned by "bt_parse_entry()" and "bt_parse_entry_s()" (see bt_input) as well as "bt_next_entry()" (which traverses a list of entries
       returned from "bt_parse_file()"---see bt_traversal).  Whole entries may be post-processed with "bt_postprocess_entry()".

       You may also need to post-process a single field, or just the value associated with it.	(The difference is that processing the field can
       change the field name---e.g. to lowercase---in addition to the field value.)  The "(field,"AuThOr")" node above is an example of a field
       sub-AST, and "(string,"Bob   Jones")" is the first node in the list of simple values representing that field's value.  (Recall that a field
       value is, in general, a list of simple values.)	Field nodes are returned by "bt_next_field()", value nodes by "bt_next_value()".  The
       former may be passed to "bt_postprocess_field()" for post-processing, the latter to "bt_postprocess_value()".

       Finally, individual strings may wander into your program from many places other than a btparse AST.  For that reason,
       "bt_postprocess_string()" is available for post-processing arbitrary strings.

   Post-processing options
       All of the post-processing routines have an "options" parameter, which you can use to fine-tune the post-processing.  (This is just like
       the per-metatype string-processing options that you can set before parsing entries; see "bt_set_stringopts()" in bt_input.)  Like elsewhere
       in the library, "options" is a bitmap constructed by or'ing together various predefined constants.  These constants and their effects are
       documented in "String processing option macros" in btparse.

       bt_postprocess_string ()
	      void bt_postprocess_string (char * s,
					  btshort options)

	   Post-processes an individual string, "s", which is modified in place.  The only post-processing option that makes sense on individual
	   strings is whether to collapse whitespace according to the BibTeX rules; thus, if "options & BTO_COLLAPSE" is false, this function has
	   no effect.  (Although it makes a complete pass over the string anyways.  This is for future expansion.)

	   The exact rules for collapsing whitespace are simple: non-space whitespace characters (tabs and newlines mainly) are converted to
	   space, any strings of more than one space within are collapsed to a single space, and any leading or trailing spaces are deleted.
	   (Ensuring that all whitespace is spaces is actually done by btparse's lexical scanner, so strings in btparse ASTs will never have
	   whitespace apart from space.  Likewise, any strings passed to bt_postprocess_string() should not contain non-space whitespace
	   characters.)

       bt_postprocess_value ()
	      char * bt_postprocess_value (AST *   value,
					   btshort  options,
					   boolean replace);

	   Post-processes a single field value, which is the head of a list of simple values as returned by "bt_next_value()".	All of the
	   relevant string-processing options come into play here: conversion of numbers to strings ("BTO_CONVERT"), macro expansion
	   ("BTO_EXPAND"), collapsing of whitespace ("BTO_COLLAPSE"), and string pasting ("BTO_PASTE").  Since pasting substrings together without
	   first expanding macros and converting numbers would be nonsensical, attempting to do so is a fatal error.

	   If "replace" is true, then the list headed by "value" will be replaced by a list representing the processed value.  That is, if string
	   pasting is turned on ("options & BTO_PASTE" is true), then this list will be collapsed to a single node containing the single string
	   that results from pasting together all the substrings.  If string pasting is not on, then each node in the list will be left intact,
	   but will have its text replaced by processed text.

	   If "replace" is false, then a new string will be built on the fly and returned by the function.  Note that if pasting is not on in this
	   case, you will only get the last string in the list.  (It doesn't really make a lot of sense to post-process a value without pasting
	   unless you're replacing it with the new value, though.)

	   Returns the string that resulted from processing the whole value, which only makes sense if pasting was on or there was only one value
	   in the list.  If a multiple-value list was processed without pasting, the last string in the list is returned (after processing).

	   Consider what might be done to the value of the "author" field in the above example, which is the concatenation of a string, a macro,
	   and another string.	Assume that the macro "and" expands to " and ", and that the variable "value" points to the sub-AST for this
	   value.  The original sub-AST corresponding to this value is

	      (string,"Bob   Jones")
	      (macro,"and")
	      (string,"Jim Smith ")

	   To fully process this value in-place, you would call

	      bt_postprocess_value (value, BTO_FULL, TRUE);

	   ("BTO_FULL" is just the combination of all possible string-processing options: "BTO_CONVERT|BTO_EXPAND|BTO_PASTE|BTO_COLLAPSE".)  This
	   would convert the value to a single-element list,

	      (string,"Bob Jones and Jim Smith")

	   and return the fully-processed string "Bob Jones and Jim Smith".  Note that the "and" macro has been expanded, interpolated between the
	   two literal strings, everything pasted together, and finally whitespace collapsed.  (Collapsing whitespace before concatenating the
	   strings would be a bad idea.)

	   Let's say you'd rather preserve the list nature of the value, while expanding macros and converting any numbers to strings.	(This
	   conversion is trivial: it just changes the type of the node from "BTAST_NUMBER" to "BTAST_STRING".  "Number" values are always stored
	   as a string of digits, just as they appear in the file.)  This would be done with the call

	      bt_postprocess_value
		 (value, BTO_CONVERT|BTO_EXPAND|BTO_COLLAPSE,TRUE);

	   which would change the list to

	      (string,"Bob Jones")
	      (string,"and")
	      (string,"Jim Smith")

	   Note that whitespace is collapsed here before any concatenation can be done; this is probably a bad idea.  But you can do it if you
	   wish.  (If you get any ideas about cooking up your own value post-processing scheme by doing it in little steps like this, take a look
	   at the source to "bt_postprocess_value()"; it should dissuade you from such a venture.)

       bt_postprocess_field ()
	      char * bt_postprocess_field (AST *   field,
					   btshort  options,
					   boolean replace);

	   This is little more than a front-end to "bt_postprocess_value()"; the only difference is that you pass it a "field" AST node (eg. the
	   "(field,"AuThOr")" in the above example), and that it transforms the field name in addition to its value.  In particular, the field
	   name is forced to lowercase; this behaviour is (currently) not optional.

	   Returns the string returned by "bt_postprocess_value()".

       bt_postprocess_entry ()
	      void bt_postprocess_entry (AST *	entry,
					 btshort options);

	   Post-processes all values in an entry.  If "entry" points to the AST for a "regular" or "macro definition" entry, then the values are
	   just what you'd expect: everything on the right-hand side of a field or macro "assignment."	You can also post-process comment and
	   preamble entries, though.  Comment entries are essentially one big string, so only whitespace collapsing makes sense on them.
	   Preambles may have multiple strings pasted together, so all the string-processing options apply to them.  (And there's nothing to
	   prevent you from using macros in a preamble.)

btparse, version 0.63						    2012-05-12				       btparse::doc::bt_post_processing(3)