identity function with an echo side effect
in [Lisp]
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From: bolega on 10 Aug 2010 16:56 After searching google groups and emacs apropos extensively, I could not find a function, perhaps I am missing one that can return identically return its argument and has a small side effect of echoing the argument in some place such as for example the mini buffer or the point at which C-x C-e is typed. For example, calling this function "echo" , usage would look like this : (cdr ( echo (cdr (echo (cdr (echo '(a b c d))))))) echo: '(a b c d) or (a b c d) (I am not sure which would be appropriate) (b c d) (c d) result: (d) Is there a need for quotes to prevent evaluation of alphabets at any phase ? Thanks.
From: Pascal J. Bourguignon on 10 Aug 2010 19:03 bolega <gnuist006(a)gmail.com> writes: > After searching google groups and emacs apropos extensively, I could > not find a function, perhaps I am missing one that can return > identically return its argument and has a small side effect of echoing > the argument in some place such as for example > > the mini buffer or the point at which C-x C-e is typed. > > For example, calling this function "echo" , usage would look like > this : > > (cdr ( echo (cdr (echo (cdr (echo '(a b c d))))))) > > echo: > '(a b c d) or (a b c d) (I am not sure which would be appropriate) > (b c d) > (c d) > > result: > (d) > > Is there a need for quotes to prevent evaluation of alphabets at any > phase ? In Common Lisp, you can use PRINT for this. CL-USER> (cdr (print (cdr (print (cdr (print '(a b c d))))))) (A B C D) (B C D) (C D) (D) CL-USER> In emacs lisp too, but the output of print goes to the *Message* buffer. M-x ielm RET ELISP> (cdr (print (cdr (print (cdr (print '(a b c d))))))) (d) and you get: (a b c d) (b c d) (c d) in the minibuffer and in *Message*. Or, in an emacs lisp buffer: (cdr (print (cdr (print (cdr (print '(a b c d))))))) C-u C-x C-e inserts: (a b c d) (b c d) (c d) (d) -- __Pascal Bourguignon__ http://www.informatimago.com/
From: bolega on 11 Aug 2010 01:01 On Aug 10, 4:03 pm, p...(a)informatimago.com (Pascal J. Bourguignon) wrote: > bolega <gnuist...(a)gmail.com> writes: > > After searching google groups and emacs apropos extensively, I could > > not find a function, perhaps I am missing one that can return > > identically return its argument and has a small side effect of echoing > > the argument in some place such as for example > > > the mini buffer or the point at which C-x C-e is typed. > > > For example, calling this function "echo" , usage would look like > > this : > > > (cdr ( echo (cdr (echo (cdr (echo '(a b c d))))))) > > > echo: > > '(a b c d) or (a b c d) (I am not sure which would be appropriate) > > (b c d) > > (c d) > > > result: > > (d) > > > Is there a need for quotes to prevent evaluation of alphabets at any > > phase ? > > In Common Lisp, you can use PRINT for this. > > CL-USER> (cdr (print (cdr (print (cdr (print '(a b c d))))))) > > (A B C D) > (B C D) > (C D) > (D) > CL-USER> > > In emacs lisp too, but the output of print goes to the *Message* buffer. > > M-x ielm RET > ELISP> (cdr (print (cdr (print (cdr (print '(a b c d))))))) > (d) > > and you get: > > (a b c d) > > (b c d) > > (c d) > > in the minibuffer and in *Message*. > > Or, in an emacs lisp buffer: > > (cdr (print (cdr (print (cdr (print '(a b c d))))))) C-u C-x C-e > > inserts: > > (a b c d) > > (b c d) > > (c d) > (d) > > -- > __Pascal Bourguignon__ http://www.informatimago.com/ THANKS A LOT !!! If you dont mind, how many years have you spent on learning emacs/ lisp ? Can you kindly give a reading syllabus, books list and possibly time for completion from your perspective and what to get out of each book since they have some common repetition. Are there any implicit quotations taking place in the above sequence of cdr, print ... ? Bolega
From: Pascal J. Bourguignon on 11 Aug 2010 10:19 bolega <gnuist006(a)gmail.com> writes: > On Aug 10, 4:03�pm, p...(a)informatimago.com (Pascal J. Bourguignon) > wrote: >> bolega <gnuist...(a)gmail.com> writes: >> > After searching google groups and emacs apropos extensively, I could >> > not find a function, perhaps I am missing one that can return >> > identically return its argument and has a small side effect of echoing >> > the argument in some place such as for example >> >> > the mini buffer or the point at which C-x C-e is typed. >> >> > For example, calling this function "echo" , usage would look like >> > this : >> >> > (cdr ( echo (cdr (echo (cdr (echo '(a b c d))))))) >> >> > echo: >> > '(a b c d) or (a b c d) �(I am not sure which would be appropriate) >> > (b c d) >> > (c d) >> >> > result: >> > (d) >> >> > Is there a need for quotes to prevent evaluation of alphabets at any >> > phase ? No. Expressions are evaluated only by EVAL or LOAD (and at compilation time, compilation time expressions by COMPILE and COMPILE-FILE). Otherwise, values are just values, they don't get evaluated magically (for what reason should they?) >> In Common Lisp, you can use PRINT for this. >> >> CL-USER> (cdr (print (cdr (print (cdr (print '(a b c d))))))) >> >> (A B C D) >> (B C D) >> (C D) >> (D) >> CL-USER> >> [...] > > If you dont mind, how many years have you spent on learning emacs/ > lisp ? 20 years. > Can you kindly give a reading syllabus, books list and possibly time > for completion from your perspective and what to get out of each book > since they have some common repetition. http://www.cliki.net/admin/search?words=books In particular, I like to advise: Common Lisp: A Gentle Introduction to Symbolic Computation http://www-cgi.cs.cmu.edu/afs/cs.cmu.edu/user/dst/www/LispBook/index.html http://www.cs.cmu.edu/~dst/LispBook/ > Are there any implicit quotations taking place in the above sequence > of cdr, print ... ? Since CDR and PRINT are function, no implicit quotation occurs: the result values are directly passed as argument to the next function. Only macros receive their arguments un-evaluated, which could be characterized as an "implicit quotation". -- __Pascal Bourguignon__ http://www.informatimago.com/
From: Captain Obvious on 11 Aug 2010 10:42 b> If you dont mind, how many years have you spent on learning emacs/ b> lisp ? I think I've learned about PRINT function on my first day learning CL. It is not terribly hard to understand what it does without even reading documentation: * (print "foobar") "foobar" "foobar" You see two foobars -- one is printed and another is returned. If you're using SLIME they will be in different colors.
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