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Re: How to prepare a regexp as arg for a funcall?


From: Barry Margolin
Subject: Re: How to prepare a regexp as arg for a funcall?
Date: Fri, 22 Feb 2013 15:01:15 -0500
User-agent: MT-NewsWatcher/3.5.3b3 (Intel Mac OS X)

In article <address@hidden>,
 Thorsten Jolitz <address@hidden> wrote:

> Hi List, 
> 
> I want to use (funcall `(occur ,REGEXP)) in a program, but encounter
> unexpected problems in preparing the regexp with the right numbers of
> '\'. 

Forgetting the regexp problem, what do you expect that to do? The first 
argument to funcall should be a function, not a list like (occur 
whatever).  

> 
> I have a string that contains one or several "*" which must be escaped
> with '\' before using it as regexp. I would think that
> 'replace-regexp-in-string' is the right tool for this - but no matter
> how many '\' I use, either 'occur or 'replace-regexp-in-string gives me
> an error.

The error in Backtrace 1 has nothing to do with how you fix up the 
regexp. It's complaining about what I wrote above: (occur ";; \\* ") is 
not a function, so you can't use it as the first argument to funcall.

> 
> The attachment below demonstrates the problem, I hope it speaks for
> itself (assume the following is the content of the *scratch* buffer): 
> 
> ;; * Function
> 
> (defun call-occur ()
>   (let ((rgxp
>          (replace-regexp-in-string
>           "*"                           ;REGEXP
>           "\\\\*"                       ;REP
>           ";; * ")))                    ;STRING
>   (funcall `(occur ,rgxp))))
> 
> (call-occur)

(defun call-occur ()
  (let ((rgxp (regexp-quote ";; * ")))
    (occur rgxp)))

> 
> 
> 
> ;; * Backtrace 1 (REP = "\\\\*")
> 
> ,-------------------------------------------------------------------
> | Debugger entered--Lisp error: (invalid-function (occur ";; \\* "))
> |   (occur ";; \\* ")()
> |   funcall((occur ";; \\* "))
> |   (let ((rgxp (replace-regexp-in-string "*" "\\\\*" ";;
> |   * "))) (funcall (\` (occur (\, rgxp)))))
> |   call-occur()
> |   [...]
> `-------------------------------------------------------------------
> 
> 
> ;; * Backtrace 2 (REP = "\\*)
> 
> ,-----------------------------------------------------------------------------
> ---
> | Debugger entered--Lisp error: (error "Invalid use of `\\' in replacement 
> text")
> |   replace-match("\\*" nil nil "*" nil)
> |   replace-regexp-in-string("*" "\\*" ";; * ")
> |   (let ((rgxp (replace-regexp-in-string "*" "\\*" ";;
> |   * "))) (funcall (\` (occur (\, rgxp)))))
> |   call-occur()
> |   [...]
> `-----------------------------------------------------------------------------
> --
> 
> ;; * M-: (occur REGEXP)
> 
> in this buffer with REGEXP:
>  
> 1. ";; \\\\* "
> 
> ,--
> | t
> `--
> 
> 2. ";; \\* "
> 
> ,--------------------------------------------------------
> | 6 matches for ";; \* " in buffer: *scratch*
> |       1:;; * Function
> |       8:          ";; * ")))                    ;STRING
> |      15:;; * Backtrace 1 (REP = "\\\\*")
> |      28:;; * Backtrace 2 (REP = "\\*)
> |      33:|   replace-regexp-in-string("*" "\\*" ";; * ")
> |      40:;; * M-: (occur REGEXP)
> `--------------------------------------------------------
> 
> [This is what I want. Why doesn't it work with '(funcall '(occur ..))?]

-- 
Barry Margolin, address@hidden
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***


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