Send {expr} over {handle}. The {expr} is encoded according to the type of channel. The function cannot be used with a raw channel. See |channel-use|. {handle} can be a Channel or a Job that has a Channel. When using the "lsp" channel mode, {expr} must be a |Dict|. {options} must be a Dictionary. It must not have a "callback" entry. It can have a "timeout" entry to specify the timeout for this specific request. ch_evalexpr() waits for a response and returns the decoded expression. When there is an error or timeout it returns an empty |String| or, when using the "lsp" channel mode, returns an empty |Dict|. Note that while waiting for the response, Vim handles other messages. You need to make sure this doesn't cause trouble. Can also be used as a |method|: GetChannel()->ch_evalexpr(expr)