[Info-vax] defining a symbol as an action invoked when entered as command

[Jim]

On Saturday, March 28, 2020 at 4:45:30 PM UTC-4, hb wrote:
> On 3/28/20 5:15 PM, Phillip Helbig (undress to reply) wrote:
> > In article <r5nqfq$7va$1 at dont-email.me>, Stephen Hoffman
> > <seaohveh at hoffmanlabs.invalid> writes:
> > 
> >> As for your DCL question, the usual solution is to write part of the
> >> DCL procedure at run-time, and then execute it.
> > 
> > Yes, but considering that a one-line procedure can be called to do the
> > job, I can write it once and just define a symbol to call it.  It's not
> > a big deal; I was just wondering whether it could be done ("define a
> > symbol which when executed defines a logical name with the value of the
> > current path as the value").
> > 
> 
>  From the fine manuals ...
> 
> DCL evaluates symbols and lexical functions preceded by apostrophes in 
> phase one (of command processing). DCL evaluates a symbol if it is used 
> as a command in phase two. Also in phase two symbols preceded by 
> ampersands are evaluated. Ampersand only applies to symbols, not to 
> lexical functions. Then in phase three there is expression evaluation.
> 
> As you probably noticed, what you want to do works for "write":
> 
> $ t = "write sys$output f$time()"
> $ t
> 28-MAR-2020 16:10:09.44
> $ t
> 28-MAR-2020 16:10:10.62
> $
> 
> As you also may have noticed, here is no substitution character at all. 
> This works because write accepts as second parameter an "$expression" 
> and expressions are evaluated by DCL as explained above, where an 
> expression can consist of symbols and lexical functions.
> 
> Have a look at sys$update:dclint.cld, where "define" is defined. 
> "parameter p2" is of type "$old_file". Change the type to "$expression" 
> and do a set command. Now you can set up your (global) symbol as "define 
> here f$env(""procedure"")" and use the symbol as a command.
> 
> If you can live with the implications of the different type, you have a 
> solution.

Very nice... and, rather than modify the current definition of DEFINE maybe just create a new one, say DEFHERE, using a modified extraction of the command definition in that file to create a new DCL verb.

If I didn't make any typos this should work...

$ create defhere.cld
$deck
define type tran_attr
        keyword concealed
        keyword terminal

define type name_attr
        keyword confine
        keyword no_alias

! order of quals must be maintained
define verb defxxx
        cliroutine define
        prefix cli$k_defi_
        parameter p1,prompt="Log name",value(required,type=$outlog)
        parameter p2,prompt="Equ name",value(required,type=$expression,list)
        qualifier system
        qualifier group
        qualifier job
        qualifier process
        qualifier user_mode
        qualifier supervisor_mode
        qualifier executive_mode
        qualifier table,value(required)
        qualifier log
        qualifier name_attributes,
                value(type=name_attr,list)
        qualifier translation_attributes,.
                  placement=positional,
                  value(type=tran_attr,list)
        qualifier cluster_system
        qualifier reserved
$eod
$ set command/replace defhere.cld
$ x = "defxxx here f$environment(""default"")"
$ x