ack/util/LLgen/LLgen.1

.\" $Header$
.TH LLGEN 1ACK
.ad
.SH NAME
LLgen, an extended LL(1) parser generator
.SH SYNOPSIS
\fBLLgen\fP
[
\fB\-vxw\fP
]
[
\fB\-j\fP[\fInum\fP]
]
[
\fB\-l\fP\fInum\fP
]
[
\fB\-h\fP\fInum\fP
]
file ...
.SH DESCRIPTION
\fILLgen\fP
converts a context-free grammar into a set of
functions which form a recursive descent parser with no backtrack.
The grammar may be ambiguous;
ambiguities can be broken by user specifications.
.PP
\fILLgen\fP
reads each
\fIfile\fP
in sequence.
Together, these files must constitute a context-free grammar.
For each file,
\fILLgen\fP
generates an output file, which must be compiled by the
C-compiler.
In addition, it generates the files
\fILpars.c\fP
and
\fILpars.h.\fP
\fILpars.h\fP
contains the
\fIdefine\fP
statements that associate the
\fILLgen\fP-assigned `token-codes' with user declared `token-names'.
This allows other source files, for instance the source file
containing the lexical analyzer,
to access the token-codes by
using the token-names.
\fILpars.c\fP
contains the error recovery routines and tables. It must also
be compiled by the C-compiler.
.PP
\fILLgen\fP
will only update those output files that differ from their previous
version.
This allows
\fILLgen\fP
to be used with
\fImake\fP
(I) convieniently.
.PP
To obtain a working program, the user must also supply a
lexical analyzer, as well as
\fImain\fP
and
\fILLmessage\fP,
an error reporting routine;
\fILex\fP
(I) is a useful program for creating lexical analysers usable
by
\fILLgen\fP.
.PP
\fILLgen\fP accepts the following flags:
.IP \fB\-v\fP
create a file called
\fILL.output\fP,
which contains a description of the conflicts that
were not resolved.
If the flag is given more than once,
\fILLgen\fP
will be more "verbose".
If it is given three times, a complete description of the
grammar will be supplied.
.IP \fB\-x\fP
the sets that are computed are extended with the nonterminal
symbols and these extended sets are also included in the
\fILL.output\fP
file.
.IP \fB\-w\fP
no warnings are given.
.IP \fB\-j\fP[\fInum\fP]
when this flag is given, \fILLgen\fP will generate dense switches,
so that the compiler can generate a jump table for it. This will only be
done for switches that have density between
\fIlow_percentage\fP and \fIhigh_percentage\fP, as explained below.
Usually, compilers generate a jumptable when the density of the switch
is above a certain threshold. If you want jump tables in more cases,
set \fIhigh_percentage\fP to this threshold, and \fIlow_percentage\fP to
a minimum threshold. There is a time-space trade-off here.
.I num
is the minimum number of cases in a switch for the \fB\-j\fP option to be
effective. The default value (if
.I num
is not given) is 8.
.IP \fB\-l\fP\fInum\fP
The \fIlow_percentage\fP, as described above. Default value is 10.
.IP \fB\-h\fP\fInum\fP
The \fIhigh_percentage\fP, as described above. Default value is 30.
.SH FILES
LL.output                 verbose output file
.br
Lpars.c                   the error recovery routines
.br
Lpars.h                   defines for token names
.SH "SEE ALSO"
\fIlex\fP (I)
.br
\fImake\fP (I)
.br
\fILLgen, an Extended LL(1) Parser Generator\fP
by C.J.H. Jacobs.
.SH DIAGNOSTICS
Are intended to be self-explanatory. They are reported
on standard error. A more detailed report is found in the
\fILL.output\fP
file.
.SH BUGS
Because some file names are fixed, at most one
\fILLgen\fP
process can be active in a given directory at
a time.
.SH AUTHOR
Ceriel J. H. Jacobs