.z.ps:f

Where f is a nary function, .z.ps is evaluated with the object that is passed to this kdb+ session via an asynchronous request. The return value is discarded.

.z.ps can be unset with \x .z.ps, which restores the default behavior.

The default behavior is equivalent to setting .z.ps to value.

Note that .z.ps is used in preference to .z.pg when messages are sent to the local process using handle 0.

q).z.ps:{[x]0N!(`zps;x);value x}
q).z.pg:{[x]0N!(`zpg;x);value x}
q)0 "2+2"
(`zps;"2+2")
4