Crash is a minimalistic command language for Crack programs. It is inspired by TCL, but diverges from the TCL language in some respects.
This repository also includes several somewhat unrelated variations on the Crash concept, including the second-generation parser and the javascript implementation of something vaguely similar.
You'll need to build and install Crack first.
After doing so, you can build the minimal command-line interface as follows:
$ crackc crash
This will create a crash.bin file that can be run directly. You may also
simply run the crash script itself, it will JIT compile itself using
crack.
Hello world:
$ print 'hello world\n' # Text after a pound sign is a comment.
hello world
null
The trailing "null" is the return value from the print command, printed by the command line evaluator.
Strings are single-quote delimited, all C escape sequences are supported. Curly-bracket enclosed text is also treated as a string, but newline escape sequences are ignored:
$ print {hello world\n}
hello world\nnull
Curly bracketed strings also allow nested (but balanced) curly brackets:
$ print {hello {world}}
hello {world}null
Other commands can be used as sub-expressions by enclosing them in square brackets:
$ print [+ 1 2]
3null
Variables are declared in a given context using the var command and accessed
with the dollar-sign prefix:
$ var three 'help comment for the three variable' [+ 1 2]
$ var x [+ 1]
$ print $three
3null
The value of a variable declared in the current context or a nested context
may be changed with the set command:
$ set x [+ $x 1] # increment x.
You can get help on all of the commands and variables in a context with the help command from "stdlib":
$ import [stdlib] help
$ help
... this would show all commands ...
$ help stdlib
... shows the help of the standard library comand ...
Arrays and fancy iteration are supported in the collections package:
$ import [collections] array arrayOf
$ var numbers [array 1 2 3 4] # These are actually strings.
You can then use an iterator, the map command and the arrayOf command to
convert them to an array of integers:
$ set numbers [arrayOf [[numbers iter] map x {+ $x}]]
We can also use filter and each methods to print only the odd values:
$ [[numbers iter] filter x {% $x 2}] each x { print $x '\n' }
See the tests and the output of the help command for more information. The
javascript implementation is undocumented, if you're interested in it see
crash_test.js.
This is not an officially supported Google product.