Define and Call a Function on a Remote Process

Question

On the server, open a connection to the client and use a synchronous request to define the following function g on the client:

g:{x+y*z}

Confirm the function was created on the client, then call it from the server with 3 arguments.

Solution

On the server:

q)\p 5001
q)clientH:hopen 5002
q)clientH(set;`g;{x+y*z})
`g

On the client (confirming):

q)g
{x+y*z}

Calling it from the server:

q)clientH(`g;2;3;4)
14

Alternative Solution

q)clientH({@[`.;`g;:;x]};{x+y*z})
`.

Explanation

clientH(set;`g;{x+y*z}) sends a sync request whose function is set, called with g and {x+y*z} as its arguments. On the client this runs `g set {x+y*z}.

Once g exists, it can be called over IPC like any built-in: clientH(`g;2;3;4) evaluates g[2;3;4] (2+3*4=14) on the client and returns it synchronously.

The alternative defines g with amend instead of set: @[`.;`g;:;x] assigns x to g in the root namespace — functionally the same.