zellerin / let-alist

Common Lisp macro let-alist modeled by Emacs lisp macro of same name

About

This Common Lisp package provides macros let-alist and let-dolist-alist that simplify access to (even buried) assoc lists.

The let-alist macro is modeled by Emacs lisp macro of same name. The rest of this section quotes Emacs documentation:

Creates a binding for each symbol used as keys the association list ALIST, prefixed with dot. This can be useful when accessing several items in the same association list, and it’s best understood through a simple example:

(let-alist '((:rose . red) (:lily . white) (:buttercup . yellow))
  (if (eq .rose 'red)
      .lily))

⇒ white

The BODY is inspected at compilation time, and only the symbols that appear in BODY with a ‘.’ as the first character in the symbol name will be bound. Finding the keys is done with ‘assoc’, and the ‘cdr’ of the return value of this ‘assoc’ is assigned as the value for the binding.

Nested association lists is supported:

(let-alist '((:rose . red) (:lily (:belladonna . yellow) (:brindisi . pink)))
  (if (eq .rose 'red)
      .lily.belladonna))

⇒ yellow

Nesting ‘let-alist’ inside each other is allowed, but the code in the inner ‘let-alist’ can’t access the variables bound by the outer ‘let-alist’.

Differencies from Emacs version

• The primary package used is KEYWORD - it means that .foo symbol (variable name) looks for :foo keyword in the alist (actually, this is what parsing from json and/or xml often ends up with)

Exported symbols

License

This is modified (translated from emacs lisp to Common Lisp) let-alist.el file from GNU Emacs. As such, it is (and needs to be) under GNU GPL.