NAME

twig - tree-manipulation language

SYNOPSIS

twig [ -sASC ] [ -w suffix ] file.mt

DESCRIPTION

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.

The input file containing the tree-specification scheme must have the suffix .mt. Twig produces two output files: walker.c, which becomes the source file for the tree matcher, and symbols.h, which contains the definitions for the node and label symbols used in the source file.

To build walker.c, twig uses an internal template file, by default one appropriate for use with fprintf(2).

The options are

-A

Use a template file for ANSI/POSIX source files.

-C

Use a template file for files that use libc's print(2) routines.

-S

Use a template file for files that use fprintf(2).

-s

Do not produce a symbols.h file.

-w suffix

Use the template file /sys/lib/twig/walker.suffix.

FILES

/sys/lib/twig

System area for template files.

SOURCE

/sys/src/cmd/twig

SEE ALSO

yacc(1)
S. W. K. Tjiang, ``The Twig Reference Manual'', Computing Science Technical Report No. 120, AT&T Bell Laboratories, Murray Hill, N.J.
A. V. Aho, M. Ganapathi, and S. W. K. Tjiang, ``Code generation using tree matching and dynamic programming.''

BUGS

When tree matching fails, the debugging output is cryptic.