cvec ← ##.exit code                         ⍝ Return to calling environment.

Some "closed workspaces" like to call ⎕OFF when their task is complete. This can
can  be  irritating during testing or if the workspace was executed as part of a
continuing interactive session. [exit] infers if this is the case by determining
whether there is a six-space input prompt in the session log following the init-
ial Dyalog APL banner.

The  result is the character vector format of [exit]'s argument, preceded by the
vector '⎕OFF ' only if it decides there is no session to which to return. [code]
is typically a small integer "exit code" with 0 meaning success.

[exit] _returns_ a character vector, rather than _executing_ it, to  reduce  the
probability of accidental termination of APL during testing.

So, with a closed workspace, instead of:

    ⎕LX←'main ⋄ ⎕OFF 0'

we might prefer:

    ⎕LX←'main ⋄ ⍎ exit 0'

With the latter coding, the ⎕LX expression will exit to the session, rather than
terminating the process, if there has been any prior session interaction.


[exit] will incorrectly assume a non-interactive session to be interactive if:

1. The session output contains a line with six or more explicit leading blanks.

2. The session output has been sufficiently voluminous to cause the log to over-
   flow, losing the line with the "Dyalog APL" banner.

In both of these cases, [exit] fails safe by omitting the '⎕OFF' vector from its
result and thus prescribing a return to the session  (rather than termination of
the APL process).


        ' 0' ≡ exit 0   ⍝ in an interactive session.

    '⎕OFF 0' ≡ exit 0   ⍝ in a runtime application.

See also: refws

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