let and flet in emacs lisp

Question

I don\'t know if you would call it the canonical formulation, but to bind a local function I am advised by the GNU manual to use \'flet\':

(defun adder-with-flet         


        

Answer 1

You don't have to use flet if you do not want to. You place a function in the function cell of a local symbol defined using let as in the following example:

(let ((ALocalSymbol))
  (fset 'ALocalSymbol (lambda (x) (* 2 x)))
  (ALocalSymbol 4)
  )

Evaluating this will return 8. Do notice the quote in front of ALocalSymbol in (let ((ALocalSymbol))...). While setq quotes symbols, fset does not.

flet is a syntactic sugar of sorts. Using a plain-old let to define nil-valued symbols, allows you to choose which "cell" of a symbol to set. You could use setq to set the symbol's value cell or fset to set the function cell.

Hope this helps,

Pablo