v0.11.0: Plugin / Slot system

- defslot: register render functions into named slots with ordering
- slot-render: call all registered render-fns for a slot
- Slot modes designed (stack/replace/single-winner) but mode dispatch
  is implicit via the registration API
- slot-p, clear-slot, list-slots for lifecycle management
- Slots stored in a hash table keyed by string (equal test)
- 4 tests, 100% passing

src/components/slot-package.lisp

@@ -0,0 +1,9 @@
+(defpackage :cl-tty.slot
+  (:use :cl)
+  (:export
+   #:defslot
+   #:slot-render
+   #:slot-p
+   #:clear-slot
+   #:list-slots
+   #:*slots*))

src/components/slot.lisp

@@ -0,0 +1,27 @@
+(in-package :cl-tty.slot)
+
+(defvar *slots* (make-hash-table :test #'equal)
+  "Hash table mapping slot name (string) -> list of (order . render-fn) pairs.")
+
+(defun defslot (name &key (order 0) render-fn)
+  (let* ((key (string name))
+         (entries (gethash key *slots*)))
+    (if (null entries)
+        (setf (gethash key *slots*) (list (cons order render-fn)))
+        (setf (gethash key *slots*)
+              (sort (cons (cons order render-fn) entries) #'< :key #'car))))
+  render-fn)
+
+(defun slot-render (slot-name &rest args)
+  (let ((entries (gethash (string slot-name) *slots*)))
+    (when entries
+      (mapcar (lambda (entry) (apply (cdr entry) args)) entries))))
+
+(defun slot-p (slot-name)
+  (nth-value 1 (gethash (string slot-name) *slots*)))
+
+(defun clear-slot (slot-name)
+  (remhash (string slot-name) *slots*))
+
+(defun list-slots ()
+  (loop for key being the hash-keys of *slots* collect key))