SketchyLISP Reference Manual - Copyright (C) 2005 Nils M Holm

8 Meta Commands

8.1 Entering Meta Commands

A meta command is entered by typing a colon (:) followed by the command itself on an empty line and without any parentheses left open. Meta commands are specific to SketchyLISP and have no counterparts in R5RS Scheme.

8.2 :C - Load Conditionally

:c file

Load the content of the given file in the same way as :l, but only if the Symbol file is not bound. If a path name is specified in file, only the base name will be used to look up the associated Symbol, so both of the following examples will work:

:c x.l
:c path/x.l

This command is intended for loading mutally recursive definitions.

8.3 :D - Dump Image

:d file

Dump the complete workspace of the interpreter to the given file. The image can be re-loaded by passing the name of the image file to the interpreter at startup time:

sketchy image-file-name

8.4 :G - Garbage Collection

:g

Run garbage collection and print some statistics.

8.5 :K - Closure Print Level

:k 0|1|2 (default: 0)

The closure print level determines how much of a closure will print when the normal form of a reduction is a closure. By default, only the argument list of a closure will be included:

(letrec ((x 'foo))
    (lambda (y) (cons y x)))
=> #<closure (y)>

With :k 1 set, the body of the closure will be included, too, so the normal form of above expression would print as:

#<closure (y) (cons x y)>

Using the :k 2, the lexical context of the closure is included as well:

#<closure (y) (cons x y) ((x.foo) (cons.cons))>

Setting :k 1 or :k 0 is normally a good idea, because closures may contain self-referential structures that take infinite time to print.

8.6 :L - Load Program

:l file

Load the content of file as if typed in at the command line. Reduced expressions will not be echoed. The file name will be converted to all lower case.

8.7 :Q - Quit

:q

Quit.

8.8 :S - Statistics

:s on|off (default: off)

Switch statistics mode on or off. In statistics mode, the total number of calls to eval and the number of nodes allocated during the reduction will print after each evaluation. Here is an example:

(cons 'a 'b)
=> '(a.b)
6 calls to eval
25 nodes allocated

These statistics are not easy to interpret and do not provide much more than a rough basis for comparing algorithms. In the above example the six calls to eval are the following:

(cons (quote a) (quote b))
cons
(quote a)
quote
(quote b)
quote

The process allocates 25 nodes (which are roughly equivalent to atoms), because the interpreter itself allocates temporary storage during reduction.

8.9 :T - Trace Mode

:t [name]

Turn trace mode on/off. In trace mode, the interpreter will print each application of the specified function after reducing the arguments but before reducing the function Symbol. Each trace line will be prefixed with a plus sign (+). To turn off tracing, use :t without any argument.

8.10 :V - Version and License

:v[l]

Print version info. :Vl prints the conditions of use (license).

8.11 :W - Wrap Column

:w col (default: 0)

Set the wrap column for output lines to col (1...255). The special col value 0 disables wrap-around.