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.TH TWIG 1
.SH NAME
twig \- tree-manipulation language
.SH SYNOPSIS
.B twig
[
.B -sASC
]
[
.BI -w " suffix"
]
.I file.mt
.SH DESCRIPTION
.I Twig
converts a tree-specification scheme consisting of pattern-action
rules with associated costs into C functions that can be called
to manipulate input trees.
The C functions first find a minimum-cost covering of an input tree
using a dynamic programming algorithm and then execute
the actions associated with the patterns used in the covering.
The tree-specification scheme may allow several coverings for an input tree,
but the dynamic programming algorithm resolves any ambiguities
by selecting a cheapest covering.
.PP
The input file containing the tree-specification scheme
must have the suffix
.LR .mt .
.I Twig
produces two output files:
.BR walker.c ,
which becomes the source file for the tree matcher, and
.BR symbols.h ,
which contains the definitions for the node and label symbols used
in the source file.
.PP
To build
.BR walker.c ,
.I twig
uses an internal template file,
by default one appropriate for use with
.IR fprintf (2).
.PP
The options are
.TP "\w'\fL-w \fIsuffix\fLXX'u"
.B -A
Use a template file for ANSI/POSIX source files.
.TP
.B -C
Use a template file for files that use libc's
.IR print (2)
routines.
.TP
.B -S
Use a template file for files that use
.IR fprintf (2).
.TP
.B -s
Do not produce a
.B symbols.h
file.
.TP
.BI -w " suffix"
Use the template file
.BI /sys/lib/twig/walker. suffix\f1.
.SH FILES
.TF /sys/lib/twig
.TP
.B /sys/lib/twig
System area for template files.
.SH SOURCE
.B /sys/src/cmd/twig
.SH "SEE ALSO"
.IR yacc (1)
.br
S. W. K. Tjiang,
``The Twig Reference Manual'',
.I
Computing Science Technical Report No. 120,
AT&T Bell Laboratories,
Murray Hill, N.J.
.br
A. V. Aho, M. Ganapathi, and S. W. K. Tjiang,
``Code generation using tree matching and dynamic programming.''
.SH BUGS
When tree matching fails, the debugging output is cryptic.

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