https://github.com/ks/X.LET-STAR.git
git clone 'https://github.com/ks/X.LET-STAR.git'
(ql:quickload :x.let-star)
X.LET-STAR is a binding/destructuring utility for Common Lisp which currently combines:
a) let* b) destructuring-bind c) :mval - multiple-value-bind d) :slot - with-slots e) :slotval - “projection” of slot values of structure/object to local variables, avoiding slot lookup every time the slot value is used in the scope of let* f) :accessor - with-accessors g) :accessorval - “projection” of values retrieved by accessor function to local variables (same concept as e) ) h) :all - binding of a group of variables to one initialization value i) destructuring of arrays j) :complex - destructuring of complex numbers
Destructuring of lists, arrays and multiple values can contain nested other binders, and also recognizes “don't care” variable _.
A small example of nested sequences destructuring:
(defstruct xxx a b)
(let* (((:mval #(x (y (:complex r i) &rest rest) (:slotval a b)) (f g)) (values (vector 10 (list 20 (complex 30 40) 50 60) (make-xxx :a 70 :b 80)) (list 90 100)))) (values x y r i rest a b f g))
It's trivially extendible with DEFINE-BINDER macro, and supports adding of customized declarations via DEFINE-DECLARATION-PROCESSING macro.
It's designed as drop-in replacement of common-list:let* (without any changes in sources needed) and as almost drop-in replacement for metabang-bind.
X.LET-START shadows common-lisp:let* (since it's completely compatible with common-lisp:let*) To use the X.LET-STAR library, your defpackage should roughly look as:
(defpackage :your-lib (:use :common-lisp :x.let-star …) (:shadowing-import-from x.let-star let*) ;; the important line …)
Example of other features:
(defstruct xxx a b c)
(let* (((_ (e . _) &key (g :xxx)) '(:sdfg (:wert :dfg :tyu) :g 100)) ;; b ((:mval h _) (rem 1234 34)) ;; c ((:slot a (b-first b)) (make-xxx :a 123)) ;; d ((:slotval (b-second b) c) (make-xxx :b 3245 :c 3456)) ;; e ((:all x y z) :init)) ;; f (values e g h a b-first b-second c x y z))
=⇒
:WERT 100 10 123 NIL 3245 3456 :INIT :INIT :INIT
expansion:
(DESTRUCTURING-BIND ;; b (#:IGNORE-1021 (E . #:IGNORE-1022) &KEY (G :XXX)) ;; b '(:SDFG (:WERT :DFG :TYU) :G 100) ;; b (DECLARE (IGNORE #:IGNORE-1021) (IGNORE #:IGNORE-1022)) ;; b (MULTIPLE-VALUE-BIND ;; c (H #:IGNORE-1020) ;; c (REM 1234 34) ;; c (DECLARE (IGNORE #:IGNORE-1020)) ;; c (WITH-SLOTS (A (B-FIRST B)) (MAKE-XXX :A 123) ;; d (LET ((#:VAL1019 (MAKE-XXX :B 3245 :C 3456))) ;; e (LET ((B-SECOND (SLOT-VALUE #:VAL1019 'B))) ;; e (LET ((C (SLOT-VALUE #:VAL1019 'C))) ;; e (LET ((#:VAL1139 :INIT)) ;; f (LET ((X #:VAL1139) (Y #:VAL1139) (Z #:VAL1139)) ;; f (VALUES E G H A B-FIRST B-SECOND C X Y Z)))))))))
More binders will be added in future as the need arises.