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This library describes a mechanism known as hooks. Hooks are a certain kind of extension point in a program that allows interleaving the execution of arbitrary code with the execution of the program without introducing any coupling between the two.
The use of hooks is pervasive in GNU Emacs and many other programs that offer some “plugin” mechanism that is built on top a facility similar to what this library offers.
While building programs, there is a need to offer extension points to allow the user to extend and customize the execution of the program in way that avoids coupling. This library wants to help with that.
This specification describes one disjoint type called
hook.
(make-hook arity)Create a hook object for storing procedures of
ARITY. The return value is a hook
object.
(hook? obj)Return #t if obj is a hook.
Otherwise, it returns #f.
(list->hook arity lst)Create a hook with the given procedures LST
that must have an arity equal to ARITY. The return value
is a hook object.
(list->hook! hook lst)Replace procedures in HOOK by the procedures in LST.
The return value is unspecified
(hook-add! hook proc)Add the procedure PROC to the HOOK
object. The return value is not specified. An implementation may
check that the arity of PROC is equal to the arity
of the HOOK.
(hook-delete! hook proc)Delete the procedure PROC from the
HOOK object. The return value is not specified.
(hook-reset! hook)Remove all procedures from the HOOK object. The
return value is not specified.
(hook->list hook)Convert the list of procedures of HOOK object to
a list.
(hook-run hook . args)Apply all procedures from HOOK to the arguments
ARGS. The order of the procedure application is not
specified. The return value is not specified. It is an error if
the length of ARGS is not equal to the arity of the
HOOK object.
In a Scheme with invokable objects, hooks can invoked directly.
A portable sample implementation is provided.
This specification is based on the GNU Guile module called hook.
Copyright © Amirouche Boubekki (2019).
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The above copyright notice and this permission notice (including the next paragraph) shall be included in all copies or substantial portions of the Software.
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