.\"	$Id: mdoc.3,v 1.49 2010/08/20 01:02:07 schwarze Exp $
.\"
.\" Copyright (c) 2009, 2010 Kristaps Dzonsons <kristaps@bsd.lv>
.\" Copyright (c) 2010 Ingo Schwarze <schwarze@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: August 20 2010 $
.Dt MDOC 3
.Os
.Sh NAME
.Nm mdoc ,
.Nm mdoc_alloc ,
.Nm mdoc_endparse ,
.Nm mdoc_free ,
.Nm mdoc_meta ,
.Nm mdoc_node ,
.Nm mdoc_parseln ,
.Nm mdoc_reset
.Nd mdoc macro compiler library
.Sh SYNOPSIS
.In mandoc.h
.In mdoc.h
.Vt extern const char * const * mdoc_macronames;
.Vt extern const char * const * mdoc_argnames;
.Ft "struct mdoc *"
.Fo mdoc_alloc
.Fa "struct regset *regs"
.Fa "void *data"
.Fa "mandocmsg msgs"
.Fc
.Ft int
.Fn mdoc_endparse "struct mdoc *mdoc"
.Ft void
.Fn mdoc_free "struct mdoc *mdoc"
.Ft "const struct mdoc_meta *"
.Fn mdoc_meta "const struct mdoc *mdoc"
.Ft "const struct mdoc_node *"
.Fn mdoc_node "const struct mdoc *mdoc"
.Ft int
.Fo mdoc_parseln
.Fa "struct mdoc *mdoc"
.Fa "int line"
.Fa "char *buf"
.Fc
.Ft int
.Fn mdoc_reset "struct mdoc *mdoc"
.Sh DESCRIPTION
The
.Nm mdoc
library parses lines of
.Xr mdoc 7
input
into an abstract syntax tree (AST).
.Pp
In general, applications initiate a parsing sequence with
.Fn mdoc_alloc ,
parse each line in a document with
.Fn mdoc_parseln ,
close the parsing session with
.Fn mdoc_endparse ,
operate over the syntax tree returned by
.Fn mdoc_node
and
.Fn mdoc_meta ,
then free all allocated memory with
.Fn mdoc_free .
The
.Fn mdoc_reset
function may be used in order to reset the parser for another input
sequence.
See the
.Sx EXAMPLES
section for a simple example.
.Pp
This section further defines the
.Sx Types ,
.Sx Functions
and
.Sx Variables
available to programmers.
Following that, the
.Sx Abstract Syntax Tree
section documents the output tree.
.Ss Types
Both functions (see
.Sx Functions )
and variables (see
.Sx Variables )
may use the following types:
.Bl -ohang
.It Vt struct mdoc
An opaque type defined in
.Pa mdoc.c .
Its values are only used privately within the library.
.It Vt struct mdoc_node
A parsed node.
Defined in
.Pa mdoc.h .
See
.Sx Abstract Syntax Tree
for details.
.It Vt mandocmsg
A function callback type defined in
.Pa mandoc.h .
.El
.Ss Functions
Function descriptions follow:
.Bl -ohang
.It Fn mdoc_alloc
Allocates a parsing structure.
The
.Fa data
pointer is passed to
.Fa msgs .
Returns NULL on failure.
If non-NULL, the pointer must be freed with
.Fn mdoc_free .
.It Fn mdoc_reset
Reset the parser for another parse routine.
After its use,
.Fn mdoc_parseln
behaves as if invoked for the first time.
If it returns 0, memory could not be allocated.
.It Fn mdoc_free
Free all resources of a parser.
The pointer is no longer valid after invocation.
.It Fn mdoc_parseln
Parse a nil-terminated line of input.
This line should not contain the trailing newline.
Returns 0 on failure, 1 on success.
The input buffer
.Fa buf
is modified by this function.
.It Fn mdoc_endparse
Signals that the parse is complete.
Note that if
.Fn mdoc_endparse
is called subsequent to
.Fn mdoc_node ,
the resulting tree is incomplete.
Returns 0 on failure, 1 on success.
.It Fn mdoc_node
Returns the first node of the parse.
Note that if
.Fn mdoc_parseln
or
.Fn mdoc_endparse
return 0, the tree will be incomplete.
.It Fn mdoc_meta
Returns the document's parsed meta-data.
If this information has not yet been supplied or
.Fn mdoc_parseln
or
.Fn mdoc_endparse
return 0, the data will be incomplete.
.El
.Ss Variables
The following variables are also defined:
.Bl -ohang
.It Va mdoc_macronames
An array of string-ified token names.
.It Va mdoc_argnames
An array of string-ified token argument names.
.El
.Ss Abstract Syntax Tree
The
.Nm
functions produce an abstract syntax tree (AST) describing input in a
regular form.
It may be reviewed at any time with
.Fn mdoc_nodes ;
however, if called before
.Fn mdoc_endparse ,
or after
.Fn mdoc_endparse
or
.Fn mdoc_parseln
fail, it may be incomplete.
.Pp
This AST is governed by the ontological
rules dictated in
.Xr mdoc 7
and derives its terminology accordingly.
.Qq In-line
elements described in
.Xr mdoc 7
are described simply as
.Qq elements .
.Pp
The AST is composed of
.Vt struct mdoc_node
nodes with block, head, body, element, root and text types as declared
by the
.Va type
field.
Each node also provides its parse point (the
.Va line ,
.Va sec ,
and
.Va pos
fields), its position in the tree (the
.Va parent ,
.Va child ,
.Va nchild ,
.Va next
and
.Va prev
fields) and some type-specific data, in particular, for nodes generated
from macros, the generating macro in the
.Va tok
field.
.Pp
The tree itself is arranged according to the following normal form,
where capitalised non-terminals represent nodes.
.Pp
.Bl -tag -width "ELEMENTXX" -compact
.It ROOT
\(<- mnode+
.It mnode
\(<- BLOCK | ELEMENT | TEXT
.It BLOCK
\(<- HEAD [TEXT] (BODY [TEXT])+ [TAIL [TEXT]]
.It ELEMENT
\(<- TEXT*
.It HEAD
\(<- mnode*
.It BODY
\(<- mnode* [ENDBODY mnode*]
.It TAIL
\(<- mnode*
.It TEXT
\(<- [[:printable:],0x1e]*
.El
.Pp
Of note are the TEXT nodes following the HEAD, BODY and TAIL nodes of
the BLOCK production: these refer to punctuation marks.
Furthermore, although a TEXT node will generally have a non-zero-length
string, in the specific case of
.Sq \&.Bd \-literal ,
an empty line will produce a zero-length string.
Multiple body parts are only found in invocations of
.Sq \&Bl \-column ,
where a new body introduces a new phrase.
.Ss Badly-nested Blocks
The ENDBODY node is available to end the formatting associated
with a given block before the physical end of that block.
It has a non-null
.Va end
field, is of the BODY
.Va type ,
has the same
.Va tok
as the BLOCK it is ending, and has a
.Va pending
field pointing to that BLOCK's BODY node.
It is an indirect child of that BODY node
and has no children of its own.
.Pp
An ENDBODY node is generated when a block ends while one of its child
blocks is still open, like in the following example:
.Bd -literal -offset indent
\&.Ao ao
\&.Bo bo ac
\&.Ac bc
\&.Bc end
.Ed
.Pp
This example results in the following block structure:
.Bd -literal -offset indent
BLOCK Ao
	HEAD Ao
	BODY Ao
		TEXT ao
		BLOCK Bo, pending -> Ao
			HEAD Bo
			BODY Bo
				TEXT bo
				TEXT ac
				ENDBODY Ao, pending -> Ao
				TEXT bc
TEXT end
.Ed
.Pp
Here, the formatting of the
.Sq \&Ao
block extends from TEXT ao to TEXT ac,
while the formatting of the
.Sq \&Bo
block extends from TEXT bo to TEXT bc.
It renders as follows in
.Fl T Ns Cm ascii
mode:
.Pp
.Dl <ao [bo ac> bc] end
.Pp
Support for badly-nested blocks is only provided for backward
compatibility with some older
.Xr mdoc 7
implementations.
Using badly-nested blocks is
.Em strongly discouraged :
the
.Fl T Ns Cm html
and
.Fl T Ns Cm xhtml
front-ends are unable to render them in any meaningful way.
Furthermore, behaviour when encountering badly-nested blocks is not
consistent across troff implementations, especially when using  multiple
levels of badly-nested blocks.
.Sh EXAMPLES
The following example reads lines from stdin and parses them, operating
on the finished parse tree with
.Fn parsed .
This example does not error-check nor free memory upon failure.
.Bd -literal -offset indent
struct regset regs;
struct mdoc *mdoc;
const struct mdoc_node *node;
char *buf;
size_t len;
int line;

bzero(&regs, sizeof(struct regset));
line = 1;
mdoc = mdoc_alloc(&regs, NULL, NULL);
buf = NULL;
alloc_len = 0;

while ((len = getline(&buf, &alloc_len, stdin)) >= 0) {
    if (len && buflen[len - 1] = '\en')
        buf[len - 1] = '\e0';
    if ( ! mdoc_parseln(mdoc, line, buf))
        errx(1, "mdoc_parseln");
    line++;
}

if ( ! mdoc_endparse(mdoc))
    errx(1, "mdoc_endparse");
if (NULL == (node = mdoc_node(mdoc)))
    errx(1, "mdoc_node");

parsed(mdoc, node);
mdoc_free(mdoc);
.Ed
.Pp
Please see
.Pa main.c
in the source archive for a rigorous reference.
.Sh SEE ALSO
.Xr mandoc 1 ,
.Xr mdoc 7
.Sh AUTHORS
The
.Nm
library was written by
.An Kristaps Dzonsons Aq kristaps@bsd.lv .