Merge branch 'seq-let'

lisp/emacs-lisp/seq.el

@@ -4,7 +4,7 @@
 
 ;; Author: Nicolas Petton <nicolas@petton.fr>
 ;; Keywords: sequences
-;; Version: 1.5
+;; Version: 1.6
 ;; Package: seq
 
 ;; Maintainer: emacs-devel@gnu.org
@@ -40,6 +40,11 @@
 ;;
 ;; All functions are tested in test/automated/seq-tests.el
 
+;;; TODO:
+
+;; - Add a pcase macro named using `pcase-defmacro' that `seq-let'
+;; - could wrap.
+
 ;;; Code:
 
 (defmacro seq-doseq (spec &rest body)
@@ -65,6 +70,14 @@ Evaluate BODY with VAR bound to each element of SEQ, in turn.
                               (pop ,index))))
            ,@body)))))
 
+(defmacro seq-let (args seq &rest body)
+  "Bind the variables in ARGS to the elements of SEQ then evaluate BODY."
+  (declare (indent 2) (debug t))
+  (let ((seq-var (make-symbol "seq")))
+    `(let* ((,seq-var ,seq)
+           ,@(seq--make-bindings args seq-var))
+       ,@body)))
+
 (defun seq-drop (seq n)
   "Return a subsequence of SEQ without its first N elements.
 The result is a sequence of the same type as SEQ.
@@ -336,7 +349,38 @@ This is an optimization for lists in `seq-take-while'."
 (defun seq--activate-font-lock-keywords ()
   "Activate font-lock keywords for some symbols defined in seq."
   (font-lock-add-keywords 'emacs-lisp-mode
-                          '("\\<seq-doseq\\>")))
+                          '("\\<seq-doseq\\>" "\\<seq-let\\>")))
+
+(defun seq--make-bindings (args seq &optional bindings)
+  "Return a list of bindings of the variables in ARGS to the elements of SEQ.
+if BINDINGS is non-nil, append new bindings to it, and
+return BINDINGS."
+  (let ((index 0)
+        (rest-bound nil))
+    (seq-doseq (name args)
+      (unless rest-bound
+        (pcase name
+          ((pred seq-p)
+           (setq bindings (seq--make-bindings (seq--elt-safe args index)
+                                              `(seq--elt-safe ,seq ,index)
+                                              bindings)))
+          (`&rest
+           (progn (push `(,(seq--elt-safe args (1+ index))
+                          (seq-drop ,seq ,index))
+                        bindings)
+                  (setq rest-bound t)))
+          (t
+           (push `(,name (seq--elt-safe ,seq ,index)) bindings))))
+      (setq index (1+ index)))
+    bindings))
+
+(defun seq--elt-safe (seq n)
+  "Return element of SEQ at the index N.
+If no element is found, return nil."
+  (when (or (listp seq)
+            (and (sequencep seq)
+                 (> (seq-length seq) n)))
+    (seq-elt seq n)))
 
 (defalias 'seq-copy #'copy-sequence)
 (defalias 'seq-elt #'elt)