9.23 gauche.parameter - Parameters (extra)

Module: gauche.parameter

Parameters are now built-in, so you no longer need to use this module for basic parameter functionalities. This module is provided mainly so that the existing code with (use gauche.parameter) won’t get an error.

It also provides a less-frequenlty used parameter observer interface.

Function: parameter-observer-add! p proc :optional when where

{gauche.parameter} Adds proc to "observer" procedures of a parameter p. Observer procedures are called either (1) just before a new value is set to the parameter, or (2) just after the new value is set to the parameter. In case of (1), a filter procedure is already applied before a callback is called. In either case, observer procedures are called with two arguments, the old value and the new value. The return value(s) of observer procedures are discarded.

The optional when argument must be either a symbol before or after, to specify whether proc should be called before or after the value is changed. If omitted, after is assumed.

The optional where argument must be either a symbol append or prepend, to specify whether proc should be prepended or appended to the existing observer procedure list. If omitted, append is assumed.

Note: Although the parameter value itself is thread-local, the observer list is shared by all threads.

Function: parameter-observer-delete! p proc :optional when

{gauche.parameter} Deletes proc from observer procedure list of a parameter p. If proc is not in the list, nothing happens. You can give either a symbol before or after to when argument to specify from which list proc should be deleted. If when argument is omitted, proc is deleted from both lists.

Function: parameter-pre-observers p

Function: parameter-post-observers p

{gauche.parameter} Returns a hook object (see Hooks) that keeps "before" or "after" observers, respectively.

Note: Although the parameter value itself is thread-local, these hook objects are shared by all threads.