MaplePrimes - answers and comments on Question, Mission: Impossible

what is meant by "prints itself"?

acer — Tue, 01 Mar 2011 09:24:16 Z

What precisely do you mean by "prints itself"? Do you mean that calling it will produce as output the same result as would evaluating (or printing) it?

I have set interface(prettyprint=1) for these examples below.

> f:=proc() print(eval(procname)); end proc;
                 f := proc() print(eval(procname)) end proc;

> f();
proc() print(eval(procname)) end proc;

Note that the above does not work when the procedure is anonymous. But for that case, one can use the new (as of Maple 14, see here) `thisproc`,

> f:=proc() print(eval(procname)); end proc:

> %(); # NULL output, ie. it didn't succeed

> proc() print(eval(thisproc)); end proc;
proc() print(eval(thisproc)) end proc;

> %();
proc() print(eval(thisproc)) end proc;

It occurs to me that perhaps you instead mean that you want the result of calling `f` to simply be the name of f.

> f:=proc(x)
>    debugopts('callstack')[2];
> end proc:

> f();
                               f

> g:=proc() f(); end proc:
> g();
                               f

I found that callstack useful when coding a redefined version of (the protected) `userinfo` which would display results to a Text Component. This worked even when the code was run in a Maplet or other "hidden" facility, and it worked without having (access) to change or edit the original routine sources. The task was harder still -- to find out how the current parent procedure had been called. I'd meant to blog it...

Another way to get this simpler effect of printing only the current procedure's own name might be,

> f:=proc() op(1,''procname''); end proc:

> f();
                               f

Do either of those two interpretations of "prints itself" come close to your intended meaning?

acer

Explanation

hirnyk — Tue, 01 Mar 2011 10:13:38 Z

I have in mind the following: the output of

Code;

which language

acer — Tue, 01 Mar 2011 10:53:29 Z

@hirnyk Which language did you have in mind, 1D or 2D?

In the 2D Math, where a trailing semicolon is not required, here are two examples (rendered here as plaintext, but can be keyed in as seen here),

proc() Typesetting:-Typeset(thisproc()) end proc()

proc() 'thisproc'() end proc()

And for 1D Maple Notation (keeping interface(prettyprint) at its default value of 3, and operating in a Worksheet in the Standard GUI),

> proc () printf("%a;\n",('thisproc')()) end proc();
proc () printf("%a;\n",('thisproc')()) end proc();

At interface(prettyprint=1) in a Worksheet, or in the commandline interface, one of the earlier 1D notation examples works,

> proc() print(eval(thisproc)); end proc;
proc() print(eval(thisproc)); end proc;

Older versions

hirnyk — Tue, 01 Mar 2011 11:55:24 Z

@acer Thanks for your attention to my question. The answer is sure unexpected for me. Is it possible in the older versions of Maple? I use Maple 13 and your code doesn't work there.

Maple 13

acer — Tue, 01 Mar 2011 12:17:44 Z

@hirnyk This seems to work in 1D notation in Maple 13.02, 12.02, or 11.02 using the default interface(prettyprint) level of 3 in a Standard Worksheet,

> proc () local t; t := proc () debugopts('callstack')[9] end proc; printf("%s;\n",eval(t)()) end proc();
proc () local t; t := proc () debugopts('callstack')[9] end proc; printf("%s;\n",eval(t)()) end proc();

I wonder if these are suitable for inclusion here? By coincidence, a work colleague recently wrote a paradox using the term quine on my whiteboard, when I was expressing my liking of some works of the late philosopher W.V.Quine.

It works well

hirnyk — Tue, 01 Mar 2011 19:09:37 Z

@acer The code

interface(prettyprint=1):

proc() print(eval(thisproc)); end proc;

works well in Maple 13. I was hurrying in the morning so I didn't pay attention to interface(prettyprint=1): . It is my fault and I am sorry for that. Many thanks for the reference. I haven't known about W. V. Quine. The positive answer to the question means that the Maple language is a language of high level. My question was inspired by this circumstance. Thanks are made one time. Because of this I simply vote up .