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The Algae interpreter assembles your Algae statements into its own opcodes and then executes them. When you are working interactively, it does this one statement (or one block of statements) at a time. When its input comes from a file, the entire file is assembled before execution of it begins.
When Algae begins execution, it normally tries to read and
execute two startup files. The first one it tries is the file in
which it expects some of its standard functions to be defined. A
default name for this file is given when Algae is
compiled--usually it's something like
`/usr/local/lib/algae/4.3.6/algae.A'. That name can be
overridden with an environment variable called
Without this file, some of Algae's standard functions will be missing. For this reason, Algae will emit an error message and quit if it can't find the file. (That is, unless the `-S' option is specified on the command line.)
After Algae reads its standard functions, it looks for the file
`.algae' in your home directory and executes it if it's there. This
file's name can be overridden with the
variable. Execution of this file is inhibited by the `-s' command
line option. No startup files at all are read if the `-S' option
Algae supports command line arguments to request various actions. Arguments starting with `-' are options. Other arguments specify files to execute.
Option flags always begin with a hyphen. Algae supports both traditional single-letter options and mnemonic long option names. Long option names are indicated with `--' instead of `-'. Abbreviations for option names are allowed as long as they are unique.
Options which change Algae's behavior take effect before any files are executed. The order of the arguments is unimportant, with the following two exceptions:
Below is a list of options accepted by Algae. Both the short and long option names are indicated.
prof function to read the `algae.out' file and
summarize it by file and by line number.
You may wish to use the
strip function in conjunction with
strip removes the line and file information
from a function, any time spent in a call to that function gets charged
to the line from which it was called.
We've encountered several systems on which operating system bugs prevent the execution profiler from working correctly. These include a DECstation and a Titan, both with MIPS architectures. If you have such a system, then Algae should have been installed with the execution profiler disabled. In that case, you'll get an error message if you try to use the `-p' option.
systemfunction is disabled, as are "pipes" (i.e., file names that begin with the `!' character).
Restricted mode should be used whenever you deal with untrusted Algae code. Without it, a malicious provider of such code could cause major damage.
vistyle by typing M-C-j.
Any file names given on the command line are executed as input to Algae.
If no file names are given (and the
-x option is not present),
input comes from stdin. You can specify stdin explicitly with a single
hyphen, so a command line like
algae init.A -
has Algae execute `init.A' first and then read from standard input.
Several types of errors may be encountered when running Algae. The two most common are parse errors and run time errors. Parse errors occur while Algae is parsing its input statements. Run time errors occur while Algae is executing its code. In both cases, Algae prints a file name and line number associated with the error.
When executing interactively, Algae displays the primary prompt
when it is ready to read a command, and the secondary prompt when it
needs more input to complete a command. You can customize the prompt
simply by assigning a character vector to the global variable
$prompt. Its first two elements specify the primary and
secondary prompts. By default,
( "> ", " " ).
Assigning something other than a character vector to
not an error--Algae just won't give you a prompt. (Wouldn't it
be fun to accept a function? Hmm, maybe someday.)
If the GNU Readline facility is available (that is, linked with
Algae during installation), Algae normally uses it for
interactive command line editing and history. Readline's editing
commands are similar to emacs: C-f forward, C-b backward,
C-p up, and C-n down. You can change to
vi style by
typing M-C-j. The `-r' command line option forces
Algae to skip Readline processing.
If Algae receives an interrupt signal (because you pressed a
C-c on the keyboard, for example), it stops what it's doing and
returns to the prompt. (If it isn't running interactively, it simply
exits.) On Unix systems, you can also use the
kill command to
send a signal to a process.
The implementation of interrupt signal handling in Algae is necessarily a compromise. We want it to respond promptly, but not at the expense of our performance. As a result, it sometimes happens that Algae does not respond promptly to an interrupt signal. (If you find a case like this; please report it. Sometimes it's the result of an oversight.)
Sending Algae a quit signal causes an immediate, clean exit. There are various other signals which will cause Algae to terminate, but this is the one to use if you want your files closed properly, etc.
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