From e46dea130e2eb36cb0cc1956a100a0497981dc42 Mon Sep 17 00:00:00 2001
From: Colin Okay <colin@cicadas.surf>
Date: Tue, 1 Nov 2022 09:58:17 -0500
Subject: Add: pluck-nested and get-nested

---
 derrida.lisp | 16 ++++++++++++++++
 package.lisp |  4 +++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/derrida.lisp b/derrida.lisp
index c9bd495..442c890 100644
--- a/derrida.lisp
+++ b/derrida.lisp
@@ -86,3 +86,19 @@ And would return
                  else
                    collect `(,term (getf ,plist-var ',term)))))
     `(let ((,plist-var ,plist)) (symbol-macrolet ,macrolet-bindings ,@body))))
+
+
+(defun get-nested (plist-tree &rest indicators)
+  "PLIST-TREE is plist some of whose values are also
+   PLISTS. INDICATORS are keyes to the plists."
+  (if (or (null plist-tree) (null indicators))
+      plist-tree
+      (apply #'get-nested (getf plist-tree (car indicators)) (cdr indicators))))
+
+(defmacro pluck-nested (keypaths plist &body body)
+  "Pluck nested binds variables to paths into a plist tree."
+  (let ((tmp-plist (gensym "plist")))
+    `(let ((,tmp-plist ,plist)) 
+       (let ,(loop for (var . path) in keypaths
+                    collect `(,var (get-nested ,tmp-plist ,@path)))
+         ,@body))))
diff --git a/package.lisp b/package.lisp
index 62377cb..8484a30 100644
--- a/package.lisp
+++ b/package.lisp
@@ -3,4 +3,6 @@
 (defpackage #:derrida
   (:use #:cl)
   (:export #:with-plist
-           #:with-alist))
+           #:with-alist
+           #:get-nested
+           #:pluck-nested))
-- 
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