Category:TXR

TXR
This programming language may be used to instruct a computer to perform a task.

Official website

See Also:	TXR on the HOPL

Listed below are all of the tasks on Rosetta Code which have been solved using TXR.

TXR is a new text extraction language implemented in C, running on Linux and Cygwin (and possibly other POSIX platforms) as well as Windows.

The source of a TXR query is literal text except for directives and variables preceded by the @ character.

Computation evolves by textual pattern matching with implicit backtracking. Non-pattern matching activities are embedded into a pattern matching paradigm. For instance, the line

Four score and seven years ago,

is a TXR directive which matches a line of that exact text, or else fails. The following is also a directive:

<lang txr>@(bind foo "abc")</lang>

which succeeds if foo has no prior binding, or already contains "abc", but fails if foo has a binding to something other than "abc".

The success of a directive means that computation proceeds to the next directive (and, if this is a pattern match, the input position advances). Failure means that the enclosing query fails, triggering back-tracking behaviors and possibly failure of the entire query.

Extremely Simple Query

Extract first matching line from the password file. Of course, TXR matches are not restricted to single line!

<lang bash>$ txr -c '@(skip) @user:@pw:@uid:@gid:@gecos:@home:@shell' /etc/passwd</lang>

user="root"
pw="x"
uid="0"
gid="0"
gecos="root"
home="/root"
shell="/bin/bash"

Now, pre-bind the user variable first to retrieve some other user. Now @(skip) kicks into action, skipping non-matching material:

<lang bash>$ txr -Duser=sshd -c '@(skip) @user:@pw:@uid:@gid:@gecos:@home:@shell' /etc/passwd</lang>

user="sshd"
pw="x"
uid="114"
gid="65534"
gecos=""
home="/var/run/sshd"
shell="/usr/sbin/nologin"

Simple Query

Re-implement the "free" utility on Linux, showing an overview of memory use:

<lang txr>#!/usr/bin/txr -f @(next "/proc/meminfo") @(define num (n))@\

 @(local numtok)@{numtok /[0-9]+/}@(bind n @(int-str numtok 10))@\

@(end) @(gather) MemTotal: @(num TOTAL) kB MemFree: @(num FREE) kB Buffers: @(num BUFS) kB Cached: @(num CACHED) kB SwapTotal: @(num SWTOT) kB SwapFree: @(num SWFRE) kB @(end) @(bind USED @(- TOTAL FREE 10)) @(bind RUSED @(- USED BUFS CACHED)) @(bind RFREE @(+ FREE BUFS CACHED)) @(bind SWUSE @(- SWTOT SWFRE)) @(output)

              TOTAL         USED         FREE      BUFFERS       CACHED

Mem: @{TOTAL -12} @{USED -12} @{FREE -12} @{BUFS -12} @{CACHED -12} +/- buffers/cache: @{RUSED -12} @{RFREE -12} Swap: @{SWTOT -12} @{SWUSE -12} @{SWFRE -12} @(end)</lang>

Sample run:

$ ./meminfo.txr
               TOTAL         USED         FREE      BUFFERS       CACHED
Mem:          769280       647752       121528       160108       286844
+/- buffers/cache:         200800       568480
Swap:        1048568        18200      1030368

Complex Query

Here is a TXR query for computing the complete dependencies of a C source file (including system and compiler headers) on a typical GNU/Linux system, demonstrating features like parallel clauses, recursion and exception handling.

<lang txr>@(define process_file (dir file already_visited visited_out)) @ (local this_file next_file header_dir next_dir next_dir2 visited_out_next) @ (bind this_file `@dir@file`) @ (none) @ (bind already_visited this_file) @ (end) @ (merge already_visited already_visited this_file) @ (next this_file) @ (collect) @ (cases)

1. include "@*header_dir/@next_file"

@ (bind next_dir `@dir@header_dir/`) @ (or)

1. include "@next_file"

@ (bind next_dir dir) @ (or)

1. @/ */include <@*header_dir/@next_file>

@ (bind next_dir `@sys_includes@header_dir/`) @ (bind next_dir2 `@gcc_includes@header_dir/`) @ (or)

1. @/ */include <@next_file>

@ (bind next_dir sys_includes) @ (bind next_dir2 gcc_includes) @ (or)

1. @/ */include_next <@*header_dir/@next_file>

@ (bind next_dir `@gcc_includes@header_dir/`) @ (or)

1. @/ */include_next <@next_file>

@ (bind next_dir gcc_includes) @ (end) @ (try) @ (process_file next_dir next_file already_visited visited_out_next) @ (merge already_visited already_visited visited_out_next) @ (catch file_error) @ (try) @ (process_file next_dir2 next_file already_visited visited_out_next) @ (merge already_visited already_visited visited_out_next) @ (catch file_error) @ (end) @ (end) @ (end) @ (bind visited_out this_file) @ (try) @ (flatten visited_out_next) @ (merge visited_out visited_out visited_out_next) @ (catch) @ (end) @(end) @(next :args) @(cases) @*dir/@*file.@suffix @ (bind directory `@dir/`) @(or) @*file.@suffix @ (bind directory "") @(end) @(next `!gcc -print-search-dirs`) install: @gcc_install @(bind gcc_includes `@{gcc_install}include/`) @(bind sys_includes "/usr/include/") @(process_file directory `@file.@suffix` nil list_out) @(output) @(rep) @list_out@(first)@file.o:@(end) @(end)</lang>

Sample run:

$ txr dep.txr match.c
match.o: /usr/include/stdio.h /usr/include/features.h /usr/include/sys/cdefs.h /usr/include/bits/wordsize.h /usr/include/gnu/stubs.h /usr/include/gnu/stubs-32.h /usr/lib/gcc/i586-redhat-linux/4.4.1/include/stddef.h /usr/include/bits/types.h /usr/include/libio.h /usr/include/_G_config.h /usr/include/wchar.h /usr/lib/gcc/i586-redhat-linux/4.4.1/include/stdarg.h /usr/include/bits/wchar.h /usr/include/wctype.h /usr/include/endian.h /usr/include/bits/endian.h /usr/include/bits/byteswap.h /usr/include/xlocale.h /usr/include/bits/wchar2.h /usr/include/bits/wchar-ldbl.h /usr/include/gconv.h /usr/include/bits/stdio-lock.h /usr/include/bits/libc-lock.h /usr/include/pthread.h /usr/include/sched.h /usr/include/time.h /usr/include/bits/time.h /usr/include/bits/sched.h /usr/include/signal.h /usr/include/bits/signum.h /usr/include/bits/siginfo.h /usr/include/bits/sigaction.h /usr/include/bits/sigcontext.h /usr/include/asm/sigcontext.h /usr/include/linux/types.h /usr/include/linux/posix_types.h /usr/include/linux/stddef.h /usr/include/asm/posix_types.h /usr/include/asm/types.h /usr/include/asm-generic/int-ll64.h /usr/include/bits/sigstack.h /usr/include/sys/ucontext.h /usr/include/bits/pthreadtypes.h /usr/include/bits/sigthread.h /usr/include/bits/setjmp.h /usr/include/bits/libio-ldbl.h /usr/include/bits/stdio_lim.h /usr/include/bits/sys_errlist.h /usr/include/getopt.h /usr/include/ctype.h /usr/include/bits/stdio.h /usr/include/bits/stdio2.h /usr/include/bits/stdio-ldbl.h /usr/include/stdlib.h /usr/include/bits/waitflags.h /usr/include/bits/waitstatus.h /usr/include/alloca.h /usr/include/bits/stdlib.h /usr/include/bits/stdlib-ldbl.h /usr/include/string.h /usr/include/bits/string.h /usr/include/bits/string2.h /usr/include/bits/string3.h /usr/include/assert.h /usr/include/errno.h /usr/include/bits/errno.h /usr/include/linux/errno.h /usr/include/asm/errno.h /usr/include/asm-generic/errno.h /usr/include/asm-generic/errno-base.h /usr/include/dirent.h /usr/include/bits/dirent.h /usr/include/bits/posix1_lim.h /usr/include/bits/local_lim.h /usr/include/linux/limits.h /usr/include/setjmp.h config.h lib.h gc.h unwind.h regex.h /usr/include/limits.h /usr/lib/gcc/i586-redhat-linux/4.4.1/include/limits.h /usr/lib/gcc/i586-redhat-linux/4.4.1/include/syslimits.h /usr/include/bits/posix2_lim.h /usr/include/bits/xopen_lim.h stream.h parser.h txr.h utf8.h filter.h match.h