?, ??
,
quit, restart, Ctrl-C
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Running Yacas
This section describes the special commands for the Yacas interactive sessions (for example, to restart or to exit the interpreter).
These commands are not functions but special directives
that only apply while running Yacas interactively.
They should not be used in scripts.
Interactive session commands
?, ?? -- get online help
Internal function
Calling format:
Parameters:
function -- name of function or keyword to request help on
Description:
The directive ? is used to request online help while running an interactive session. A name of a function or a help keyword can be specified.
The corresponding reference manual section will be shown.
(There is a special glossary section that contains keywords and explains some of the Yacas terminology.)
Function names should be given without quotes.
Note that function names are case-sensitive in Yacas but the ? facility will also respond to all lowercase names.
The directive ?? displays the index to all documentation.
Documentation is displayed in a Web browser of your choice. The default choice is lynx.
An alternative browser can be set using the SetHelpBrowser function.
Examples:
Get help on a function:
The function name can be given in all lowercase:
Get help on a keyword:
Browse all documentation:
See also:
Help
,
SetHelpBrowser
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quit, restart, Ctrl-C -- basic session control
Internal function
Calling format:
Description:
Type quit or restart at the Yacas prompt to exit or to restart the interpreter.
The directives quit and restart are not reserved words or variable names.
They take effect only when typed as first characters at a prompt.
Pressing Ctrl-C will stop the currently running calculation.
If there is no currently running calculation, Ctrl-C will quit the interpreter.
When the interpreter quits, it saves the command history
(so quitting by Ctrl-C does not mean a "crash").
Examples:
To be effective, the directive must be typed immediately after the prompt:
We can use variables named quit:
There is no effect if we type some spaces first:
In> restart
Out> restart;
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See also:
Exit
.
Command-line options
The default operation of Yacas is to run in the interactive console mode. Yacas accepts several options that modify its operation.
Here is a summary of options:
- filename ... (read and execute a file or several files)
- -c (omit line prompts)
- -d (print default directory)
- -v (print version information)
- -f (execute standard input as one statement)
- -p (do not use terminal capabilities)
- -t (enable extra history features)
- --archive filename (use a given library archive file)
- --dlldir directory (specify default directory for plugins)
- --init filename (use a given initial file)
- --patchload (use PatchLoad to load files)
- --read-eval-print expression (call this expression for the read-eval-print loop)
- --rootdir directory (specify default directory for scripts)
- --server port (start Yacas as a network server on given port)
- --verbose-debug (turn on showing some additional debugging information on screen)
- --disable-compiled-plugins (disable loading of compiled plugins, loading the script versions instead)
- --stacksize size (change size of stack arguments are stored on)
- --execute expression (run expression from the command line)
Options can be combined, for example
will read and execute the file filename non-interactively without using terminal capabilities and without printing prompts.
Here is a more detailed description of the command-line options.
Inhibit printing of prompts In> and Out>. Useful for non-interactive sessions.
Reads standard input as one file, but executes only the first statement in it. (You may want to use a statement block to have several statements executed.)
Does not use terminal capabilities, no fancy editing on the command line and no escape sequences printed. Useful for non-interactive sessions.
Enable some extra history recall functionality in console mode: after executing a command from the history list, the next unmodified command from the history list will be automatically entered on the command line.
yacas [options] {filename}
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Reads and executes commands in the filename and exits. Equivalent to Load().
Prints version information and exits.
(This is the same information as returned by Version().)
Prints the path to the Yacas default library directory (this information is compiled into the Yacas executable) and exits.
Will load every file on the command line with the PatchLoad command instead of the normal Load command,
This is useful for generating HTML pages for a
web site using the Yacas scripting language, much like you can do with
the PHP scripting language.
Tells the system to load file as the initialization file. By default
it loads the file yacasinit.ys from the scripts directory. Thus for
customization one has two options: write a ~/.yacasrc file
with initialization code (as it is loaded after the initialization
script is loaded), or write a custom initialization script that first
uses yacasinit.ys and adds some extra custom code.
yacas --read-eval-print [expression]
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Call expression for the read-eval-print loop. The default
read-eval-print loop is implemented in the initialization
script yacasinit.ys as the function REP.
The default behavior is therefore equivalent to --read-eval-print REP().
There is also a fallback read-eval-print
loop in the kernel; it can be invoked by passing an empty
string to this command line option, as --read-eval-print "".
An alternative way to replace the default read-eval-print
loop is to write a custom initialization script that implements
the read-eval-print loop function REP() instead of yacasinit.ys.
Care has to be taken with this option because a Yacas session may
become unusable if the read-eval-print expression doesn't function correctly.
On some platforms server mode can be enabled at build time by passing the
flag --enable-server to the ./configure script. Yacas
then allows you to pass the flag --server with a port number
behind it, and the Yacas executable will listen to the socket
behind that port instead of waiting for user input on the console.
Commands can be sent to the server by sending a text line as
one block of data, and the server will respond back with another text block.
One can test this function by using telnet. First, set up
the server by calling
and then invoke telnet in another window, for example:
Then type a line of Yacas input and hit Enter.
The result will be one line that you will get back from the Yacas server.
Some security measures and resource management measures have been
taken. No more than 10 connections can be alive at any time,
a calculation cannot take more than 30 seconds, and Yacas
operates in the secure mode, much like calling an expression
by passing it as an argument to the Secure function.
This means that no system calls are allowed, and no writing to
local files, amongst other things. Something that has not been
taken care of yet is memory use. A calculation could take up all
memory, but not for longer than 30 seconds.
The server is single-threaded, but has persistent sessions for
at most 10 users at a time, from which it can service requests
in a sequenial order. To make the service multi-threaded, a
solution might be to have a proxy in front of the service listening
to the port, redirecting it to different processes which get
started up for users (this has not been tried yet).
yacas --rootdir [directory]
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Tells the system where to find the library scripts. Here, directory is a
path that is passed to DefaultDirectory. It is also possible to give a
list of directories, separated by a colon, e.g.
yacas --rootdir scripts/:morescripts/.
Note that it is not necessary to append a trailing slash to the directory names.
yacas --dlldir [directory]
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Tells the system where to find the plugins. Here directory is a
path that is passed to DllDirectory. It is also possible to give a
list of directories separated by a colon.
The default value is specified at compile time, usually /usr/local/lib/yacas.
Use a compressed archive instead of the script library.
Yacas has an experimental system where files can be compressed into
one file, and accessed through this command line option. The advantages
are:
- Smaller disk/memory use (useful if Yacas is used on small hand-held computers).
- No problems with directory path separators: "path/file" will always
resolve to the right file, no matter what platform (read: Windows) it runs on.
- The start-up time of the program might improve a little, since
a smaller file is loaded from disk (disk access being slow), and then decompressed
in memory, which might be a lot faster than loading from disk.
An additional savings is due to the fact that the script files are
stripped from white spaces and comments, making them smaller and faster loading.
To prepare the compressed library archive, run ./configure
with the command line option --enable-archive.
The result should be the archive file scripts.dat.
Then launch Yacas with the command line option --archive scripts.dat,
with the file scripts.dat in the current directory.
The reason that the scripts.dat file is not built automatically is
that it is not tested, at this time, that the build process works on all
platforms.
(Right now it works on Unix, MacOSX, and Win32.)
Alternatively, configure Yacas with
./configure --enable-archive
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and the archive file scripts.dat will be created in the ramscripts/
subdirectory.
When an archive is present, Yacas will try to load it before it looks for scripts from the library directories.
Typing
make archivetest -f makefile.compressor
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in the ramscripts/ directory runs all the test scripts using the archived
files.
The currently supported compression schemes are uncompressed
and compressed with minilzo. Script file stripping (removing whitespace
and comments) may be disabled by editing compressor.cpp (variable strip_script).
yacas --disable-compiled-plugins
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Disable loading of compiled scripts, in favor of scripts themselves.
This is useful when developing the scripts that need to be compiled
in the end, or when the scripts have not been compiled yet.
Yacas maintains an internal stack for arguments. For nested function calls, all arguments currently used are on this stack. The size of this stack is
50000 be default.
For a function that would take 4 arguments and has one return value, there would be 5 places reserved on this stack, and the function could call itself recursively 10000 steps deep.
This differs from the MaxEvalDepth mechanism. The MaxEvalDepth mechanism
allows one to specify the number of separate stack frames (number of calls,
nested), instead of the number of arguments pushed on the stack. MaxEvalDepth
was introduced to protect the normal C++ stack.
yacas --execute <expression>
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This instructs Yacas to run a certain expression, passed in over the command line, before dropping to the read-eval-print loop. This can be used to load a file before dropping to the command line without exiting (if there are files to run specified on the command line, Yacas will exit after running these scripts). Alternatively, the expression can exit the interpreter immediately by calling Exit();. When used in combination with -pc, the Yacas interpreter can be used to calculate something and print the result to standard output. Example:
user% ./yacas -pc --execute '[Echo("answer ",D(x)Sin(x));Exit();]'
answer Cos(x)
user%
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