Re: Real-life examples of lexical binding in Emacs Lisp

[Pascal J. Bourguignon]

Tassilo Horn <tsdh@gnu.org> writes:

> The emacs paper has a section explaining why emacs used dynamic binding
> from the start: http://www.gnu.org/software/emacs/emacs-paper.html#SEC17
>
> However, to me the two example use-cases only motivate why you want to
> be able to use dynamic scoping for special variables (defvar), not
> really for local variables (let) or function parameters, although the
> first Edit Picture example explicitly speaks of binding command
> arguments but I don't understand it.

Indeed, in general, you want lexical binding for local variables.

However, I would argue that for global variables, lexical binding would
be useful too, even by default.

In Common Lisp, we can implement global lexical variables, using
eg. symbol macros, but in emacs lisp, we're missing operators for the
global lexical case:

            dynamic   lexical
  global    defvar    -
  local     let(1)    let(2)

  (1) when lexical-binding is nil or the variable has been defvar'ed.
  (2) when lexical-binding is t and the variable has not been defvar'ed.


> But there are good use-cases for dynamic variables also in "normal"
> programs.  One example is to be able to bind some *error-handler*
> dynamically in order to customize how to cope with errors that happen
> far below the call stack.

Definitely.

https://groups.google.com/forum/#!original/comp.lang.lisp/oC5gDvn42pM/IudCXzCtxowJ

-- 
__Pascal Bourguignon__                 http://www.informatimago.com/
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