Terse Hashes Miscellany

This is part 4 in my terse hashes in emacs lisp series

• Terse Hashes in Emacs Lisp
• Data::Dumper in Emacs Lisp
• Terse Hash Dereferencing
• Terse Hashes Miscellany

Okay, time to wrap up with the terse hashes.

The built-in hash tables have equivalents to the perl exists and delete, but again, the argument order does not feel right to me.

Having looked at ruby a bit over the past few months, I’ve decided I like predicates ending with a question mark¹ rather than a p.

(defsubst exists? (hash key)
  (not (eq (gethash key hash 'missing-key) 'missing-key)))

(defsubst del-hash! (hash key) (remhash key hash))

And the other thing I rely on a lot in perl is keys so I can choose the traversal order with sort.

(defun keys (hash)
  (let (keys)
    (maphash (lambda (k v) (push k keys)) hash)
    keys))

I need a decent less than method

(defun generic/less (val1 val2)
  (if (and (numberp val1) (numberp val2))
      (< val1 val2)
    (let ((v1 (prin1-to-string val1))
          (v2 (prin1-to-string val2)))
      (string< v1 v2))))

and then this sort of thing just works

(defvar %hash (_h { 1 2 'a 'x 5 6 10 "lemon" }))
(sort (keys %hash) #'generic/less) ;; --> (1 5 10 a)

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1. Was this first in scheme?

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