feat(utils): add generic FUNCTIONALIZE to turn values into functions

lens.lisp

@@ -7,6 +7,23 @@
          data-lens:compress-runs data-lens:combine-matching-lists
          data-lens:juxt data-lens:element data-lens:sorted))
 
+(defgeneric functionalize (it)
+  (:method ((it hash-table))
+    (lambda (key &optional default)
+      (gethash key it default)))
+  (:method ((it vector))
+    (lambda (idx &optional default)
+      (let ((present-p (and (>= idx 0)
+                            (< idx (length it)))))
+        (values (if present-p
+                    (aref it idx)
+                    default)
+                present-p))))
+  (:method ((it symbol))
+    (fdefinition it))
+  (:method ((it function))
+    it))
+
 ;;; TODO: consider making this wrap defalias?
 (defmacro shortcut (name function &body bound-args)
   `(eval-when (:load-toplevel :compile-toplevel :execute)

package.lisp

@@ -18,8 +18,7 @@
            #:compress-runs #:combine-matching-lists #:sorted #:applicable-when
            #:of-length #:of-min-length #:of-max-length #:transform-head
            #:maximizing #:zipping #:applying #:splice-elt #:transform-elt #:denest
-           #:op #:defalias #:<> #:<>1 #:== #:•
-           ))
+           #:op #:defalias #:<> #:<>1 #:== #:• #:suffixp #:functionalize))
 
 (defpackage :data-lens.transducers.internals
   (:use :cl)

transducers.lisp

@@ -11,7 +11,9 @@
   (:method ((seq sequence) (func symbol) init)
     (reduce func seq :initial-value init))
   (:method (seq (func symbol) init)
-    (reduce-generic seq (symbol-function func) init))
+    (reduce-generic seq
+                    (symbol-function func)
+                    init))
   (:method ((seq hash-table) (func function) init)
     (let ((acc init))
       (maphash (lambda (k v)