Top-level Interaction

EusLisp's standard top-level read-eval-print loop is controlled by eustop. When EusLisp is invoked, eustop tries to load the file named ".eusrc" in your home directory or the file specified by the EUSRC environment variable. It also tries to load a file named ".eusrc" in the current working directory. So, if you are in your home directory, note that .eusrc is loaded twice. Then EusLisp loads files specified in its argument list. After these loading, eustop enters normal interactive session.

When *standard-input* is connected to user's tty, eustop prints prompt generated by the toplevel-prompt function. The default toplevel-prompt prints "eus$ ". The effect of changing the definition of toplevel-prompt appears when eustop is invoked next time. One way to change the prompt from the first time is to define toplevel-prompt in your .eusrc file.

Inputs are read from *terminal-io* stream. If the input is parenthesized, it is taken as a lisp form and is evaluated by eval. Else if the first symbol of the input line has function definition, the line is automatically parenthesized and evaluated. If no function definition is found, then its special value is examined and the value is printed. If the symbol is unbound, the line is regarded as UNIX command and passed to sh (Bourn's shell). If sh cannot find corresponding unix command, ``command unrecognized" message is printed. Thus, eustop works both as a lisp interpreter and as a unix shell. If you do not wish to execute the input as UNIX command, you may escape the form by preceeding a comma ',' at the begining of the line. This is also useful to see the dynamic value binding when an error occured in the interpretive execution. Since EusLisp adopts lexical scope, we cannot examine the value of local variables outside of the scope unless they are declared special.

If the environment variable, USE_TOP_SELECTOR, is defined, the toplevel input is read in an asynchronous manner using the select library call. The input stream (*standard-input*) is registered to the *top-selector*, which is an instance of the port-selector class, together with the read-eval-print function (repsel) Therefore arrival of key inputs invokes the evaluation of the repsel. This feature is particularly useful when EusLisp is to handle multiple events, i.e., key inputs, X window events, and socket connection requests, at the same time. In order to exploit this asynchronous toplevel interaction, users should never write a code that blocks at the read operation. Instead, the input stream should be registered to the *top-selector* with its handler function by using the :add-port method. The handler function is expected to read from the stream, which is already known ready to return the input without blocking.

Note that Xwindow event handlers are defined to use the *top-selector* implicitly when USE_TOP_SELECTOR is defined, and user programs do not have to call x:window-main-loop at all to catch X events.

Using the time-out of the select call, users may define a timer handler. Each time the select call times out, the function bound to *timer-job* is invoked with no argument. The timer interval is defined by *top-selector-interval*, which is defaulted to 10.0 second. Note that the timer function invokation is not precisely periodic when there are inputs to the *top-selector*.

In the toplevel interaction, each line input is remembered in *history* vector with a sequence number. You can recall a specific input by ! function as if you were in csh. The difference from csh's history is, you need at least one white space between the exclamaition mark and the sequence number since ! is a function, and you can edit the line interactively with control keys, as in emacs.

^D (EOF) terminates EusLisp normally. To return abnormal termination code to upper level (usually a csh), use exit with an appropriate condition code.

eustop sets a signal handler only for SIGINT and SIGPIPE, and other signals are not caught. Thus, signals such as SIGTERM or SIGQUIT cause EusLisp to terminate. In order to catch these signals to avoid termination, use unix:signal function to set user-defined signal handlers.

- [variable]

current input.

+ [variable]

previous input.

++ [variable]

old input.

+++ [variable]

ancient input.

* [variable]

previous result.

** [variable]

old result.

*** [variable]

ancient result.

*prompt-string* [variable]

prompt string used by eustop.

*program-name* [variable]

the command that invoked this EusLisp, possibly eus, eusx, eusxview or user-saved euslisp.

eustop &rest argv [function]

is the default toplevel loop.

eussig sig code [function]

is the default signal hander for SIGPIPE. eussig prints signal number upon its arrival and enters another toplevel loop.

sigint-handler sig code [function]

is the default signal handler for SIGINT (control-C). It enters a new top level session.

euserror code message &rest arg [function]

the default error handler that prints message and enters a new error session.

reset [function]

quits error loop and goes back to the outermost eustop session.

exit &optional termination-code [function]

terminates EusLisp process and returns termination-code (0..255) as the process status code (0..255).

*top-selector* [variable]

The port-selector object to handle asynchronous function invocation according to inputs from multiple streams.

h [function]

prints all the inputs remembered in *history* vector with associated sequence numbers.

! &optional (seq 0) [function]

recalls the input line associated with the sequence number seq. When seq is 0, the most recent command is recalled, and if seq is negative, the line is specified relatively to the current input. The recalled line is printed and the cursor is located at the end of the line. You can go backward by control-H (backspace) or control-B, go forward by control-F or control-K, go to the beginning of line by control-A, to the end of line by control-L. control-C cancels the line editing. control-M (carriage-return) or control-J (line-feed) finishes editing the line and starts evaluation of the edited line. If seq is not a number and is a symbol or a string, the history list is searched toward old input, and a command line which include the symbol or a string as a substring is returned.

new-history depth [function]

initializes *history* vector to have depth length. Depth input lines are remembered. All the input lines recorded in the current *history* are discarded.