function factory in elisp

1. example
Backlinks
- reference retrivial time counts in critical recall time
- emacs-lisp

1. example

return a predicate function taking 1 argument. if it is in [left,right], it will return true, otherwise fallse For example, (setq in2-3 (in-region-p-c 2 3)), then (in2-3 2.5) returns ture. [2023-05-26 Fri 13:45]

(defun hermanhel-in-region-p-c (left right)
  `(lambda (val) (< ,left val ,right))
                )
(setq in2-3 (hermanhel-in-region-p-c 2 3))
(fset 'in2-3 (hermanhel-in-region-p-c 2 3))


;; ((lambda (val) (< 2 val 3)) 2.5)
;; this works

(in2-3 2.5)
;; this won't work if not using fset

(funcall 'in2-3 2.5)
;; this would work either way(setq or fset)

note - to plug values in lambda, make a function generator, use ` and , as lambda is macro and every symbol is treated as symbol only, without evaluation note - to use function produced by factory:

if used with (funcall in2-3 2.5), define with (setq in2-3 (in-region 2 3))
if used with (in2-3 2.5), define with (fset in2-3 (in-region 2 3))

note - defmacro if you don’t want some part of argument to be evaluated¹, defun if it does not matter when the calculation is done

Backlinks

reference retrivial time counts in critical recall time

Say your critical recall time is 3 minutes, and you want to use a specific programming pattern, like function factory in elisp. It is possible that you can’t recall all critical points for writing function factory in elisp(using fest, using ` and ,, when to use defmacro, when to use defun), but if you can retrieve the reference and finish reading it in 3 minutes, you should be able to use that piece of knowledge with no friction

emacs-lisp

Footnotes:

or evaluated as lisp symbols: this is the case with loop, when there’s bunch of symbols like for and to that if interpretated as lisp symbols will produce symbol-not-defined error.