cmd

README

cmd - an example interactive shell to experiment with s-expressions

This package contains some example code that shows how to work with the packages defined in this repository. All predefined callable and syntax functions are available.

The shell produces some kind of verbose logging when it is evaluating symbolic expression. To control this logging, some additional functions are available:

• (log-reader): toggles the logging of the result of the sxreader.Read() call. The log output is prefixed with the string ";r ".
• (log-parser): toggles the logging of the result of the sxeval.Parse() call. The log output is prefixed with the string ";p ". In addition, the internal parsing steps are aslo logged. The symbolic expression to be parsed is logged with the prefix ";P ", the resulting parsed expression with the prefix ";Q ".
• (log-expr): enables logging of the result of calls to sxeval.Rework. Further processing is stopped, the resulting expression is not computed. This is to inspect the output of a (quasiquote ...) expression.
• (log-executor): toggles the logging of the computing execution. The expression to be computed is logged with the prefix ";X ", the resulting value with the prefix ";O ".
• (log-off): All loggings, except the rework log, are enabled. This command disables all logging.
• (panic EXPR): produces an internal panic (a hard error within the Go environment). The optional expression is the argument. If not given, the string "common panic" is used instead.

Some symbols are bound to specific objects:

• root-binding is bound to the root binding, where most predefined functions are defined.
• repl-binding is bound to the binding that is used in the shell. The root binding is a (possible indirect) parent binding.
• UNDEFINED is bound to the undefined value.

When the shell starts, the content of the file "prelude.sxn" is evaluated before any input is read from the user (via the reader).