Re: Factor

Factor: the language, the theory, and the practice.


Friday, July 15, 2016


Most languages support running arbitrary commands using something like the Linux system function. Often, this support has both quick-and-easy and full-featured-but-complex versions.

In Python, you can use os.system:

>>> os.system("ls -l")

In Ruby, you can use system as well as “backticks”:

irb(main):001:0> system("ls -l")

irb(main):002:0> `ls -l`

Basically, the difference between “system” and “backticks” is:

  • “system” executes a command, returning the exit code of the process.
  • “backticks” executes a command, returning the standard output of the process.

Factor has extensive cross-platform support for launching processes, but I thought it would be fun to show how custom syntax can be created to implement “backticks”, capturing and returning standard output from the process:

    "`" parse-multiline-string '[
        _ utf8 [ contents ] with-process-reader
    ] append! ;

You can use this in a similar fashion to Ruby or Perl:

IN: scratchpad ` ls -l`

Note: This syntax currently requires a space after the leading backtick. In the future, we have plans for an improved lexer that removes this requirement.

This is available in the backticks vocabulary.