Runtime library interfaces for command-line applications
========================================================

See also `environment_variables.txt`


Maybe the aspects of command-line libraries should be some injected objects.

Low level interface:

    CommandMain "mycommand"

    inject CommandEnvironment env
    inject CommandParameters params
    inject CommandExitStatus exitstatus

    entry main
        
    end

High level interface:

    CommandMain "mycommand"

    # XXX should it be possible to inject environment variables
    # into classes? maybe it's safer/clearer to not allow that?
    inject String target = from_environment "TARGET"
    inject ?Dir sourcedir = from_commandparam "--srcdir" "-s"

    # shorter syntax:
    inject
        ?String target = from_environment "TARGET"
        ?Dir sourcedir = from_commandparam "--srcdir" "-s"
        OutStream stdout = from_stdout
        OutStream stderr = from_stderr
        CommandExiter exiter = from_system
    end

    # even shorter syntax, with implied "constructor" names:
    # could even only allow one `inject` block to prevent obfuscated code.
    inject
        ?String target environ "TARGET"
        ?Dir sourcedir cmdparam "--srcdir" "-s"
        # using default "constructor"
        OutStream stdout
        OutStream stderr
        CmdExiter exiter
        # capabilities can be specified here, too
        NativeBinary somebinary with
            # scoping rules could make this possible
            stderr = stderr
            # multi-valued parameters?
            filesystem = read "/"
            filesystem = writeonly_tempdir
            exec = "somebinary"  # looked up in PATH
        end
    end

    entry main
        CapabilityWrapper cw = new
        cw.add "stderr" stderr
        cw.add "somebinary" somebinary
        SomeOperation op = new cw
        op.run sourcedir target
    end


Alternative name of the `inject` keyword?

    inject
    require
    demand
    environment
    env
    system
    request
    params
    parameters
    parametric
    config
    configuration
    unbound
    free
    dynamic
    hosted
    from_host
    provided    (ok)
    need        (ok)
    needed
    giveme      (best?)

Handling injection errors
-------------------------

    giveme
        String name httpparam
        File data resource_directory "data" 
    else
        # these are specific implementations of services
        MyMissingHttpParam new "this_page"
        MyMissingFile new "this_page"
    end