Re: (format ... "~A" (apply #'format nil errorstring arguments))

[Bruno H. <br...@cl...>]

Hi Sam,

> In clos-method2.lisp and many other places you have this pattern:
> 
> --8<---------------cut here---------------start------------->8---
> (defmacro program-error-reporter (caller)
>   `#'(lambda (form detail errorstring &rest arguments)
>        (apply #'sys::lambda-list-error form detail
>               "~S: ~A" ,caller (apply #'format nil errorstring arguments))))
> --8<---------------cut here---------------end--------------->8---
> 
> Why not
> 
> --8<---------------cut here---------------start------------->8---
> (defmacro program-error-reporter (caller)
>   `#'(lambda (form detail errorstring &rest arguments)
>        (apply #'sys::lambda-list-error form detail
>               "~S: ~?" ,caller errorstring arguments)))
> --8<---------------cut here---------------end--------------->8---

Both are equivalent. I find the first one easier to understand,
because ~S, ~A, and APPLY are very familiar to everyone, whereas I wouldn't
remember how ~? works exactly - there are two cases - without looking up
CLHS 22.3.7.6.

The other possible explanation is that FORMATTER of ~? was not completely
implemented when I wrote clos-method2.lisp, and I dared to use ~? only after
it was efficient enough.

Bruno