Re: Factor

A question was asked recently on the Factor mailing list about the Argument Parser that I had previously implemented in Factor:

I have been trying to hack on command-line.parser to add the ability to call it with commands.

The specific feature they want is similar to the ArgumentParser.add_subparsers function in Python’s argparse module. I spent a little bit of time thinking about a quick implementation that can get us started, and applied this patch to support commands.

Here’s their example of a MAIN with two commands with different options using with-commands:

MAIN: [
    H{
        {
            "add"
            {
                T{ option
                    { name "a" }
                    { type integer }
                    { #args 1 }
                }
            }
        }
        {
            "subtract"
            {
                T{ option
                    { name "s" }
                    { type integer }
                    { #args 1 }
                }
            }
        }
    } [ ] with-commands
]

We currently produce no output by default when no command is specified:

$ ./factor foo.factor

The default help prints the possible commands:

$ ./factor foo.factor --help
Usage:
    factor foo.factor [--help] [command]

Arguments:
    command    {add,subtract}

Options:
    --help    show this help and exit

Or get default help for a command:

$ ./factor foo.factor add --help
Usage:
    factor foo.factor add [--help] [a]

Arguments:
    a

Options:
    --help    show this help and exit

Or print an error if the argument is not a valid command:

$ ./factor foo.factor multiply
ERROR: Invalid value 'multiply' for option 'command'

There are other features we might want to add to this including per-command metadata with a brief description of the command, support for additional top-level options besides just the command, and perhaps a different way of handling the no command case rather than empty output.

This is available in the latest developer version!