maxima-discuss

[Maxima-discuss] How to break out of a loop with a block?

[Helmut J. <jar...@ig...>]

The documentation says:
   Note however that a return within a do that occurs in a block
   will exit only the do and not the block.

The following do does not occur within a block, so why does


RetVal:for k in [1,2,3] do block(
    if k=2 then return(7))$

print(RetVal)$

print 'done' instead of 7 ?

Thanks for an explanation and a work around,
Helmut

Re: [Maxima-discuss] How to break out of a loop with a block?

[Adam <ada...@o2...>]

W dniu 27.04.2014 11:49, Helmut Jarausch pisze:
>
> The documentation says:
>     Note however that a return within a do that occurs in a block
>     will exit only the do and not the block.
>
> The following do does not occur within a block, so why does
>
>
> RetVal:for k in [1,2,3] do block(
>      if k=2 then return(7))$
>
> print(RetVal)$
>
> print 'done' instead of 7 ?
>
> Thanks for an explanation and a work around,
> Helmut
> ------------------------------------------------------------------------------
> Start Your Social Network Today - Download eXo Platform
> Build your Enterprise Intranet with eXo Platform Software
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>


1.
"The value normally returned by a do statement is the atom done. 
However, the function return may be used inside the body to exit the do 
prematurely and give it any desired value.
Note however that a return within a do that occurs in a block will exit 
only the do and not the block. Note also that the go function may not be 
used to exit from a do into a surrounding block. " ( from do doc )


2.
It is not the answer, but result is 7 not done.
(%i1)  for k in [1,2,3] do

     if k=2 then RetValue:7 ;
(%o1) done
(%i2) RetValue;
(%o2) 7

HTH

Adam

http://commons.wikimedia.org/wiki/Category:Images_with_Maxima_CAS_source_code

Re: [Maxima-discuss] How to break out of a loop with a block?

[Stavros M. <mac...@al...>]

"return" exits from the innermost (dynamic) block surrounding it. This may
be a 'block' or a 'do'. Note that a function body is *not* a block:

block( return(3)) => 3
do return(3) => 3


​​
​In your example​, 'return' returns from the block, not from the for/do:
​​

​for k thru 3 do block( print(k), if k=2 then return(23), print(k*10) )


prints 1,10,2,3,30 and returns 'done'.

                  -s​

​​​

On Sun, Apr 27, 2014 at 5:49 AM, Helmut Jarausch <
jar...@ig...> wrote:

>
> The documentation says:
>    Note however that a return within a do that occurs in a block
>    will exit only the do and not the block.
>
> The following do does not occur within a block, so why does
>
>
> RetVal:for k in [1,2,3] do block(
>     if k=2 then return(7))$
>
> print(RetVal)$
>
> print 'done' instead of 7 ?
>
> Thanks for an explanation and a work around,
> Helmut
>
> ------------------------------------------------------------------------------
> Start Your Social Network Today - Download eXo Platform
> Build your Enterprise Intranet with eXo Platform Software
> Java Based Open Source Intranet - Social, Extensible, Cloud Ready
> Get Started Now And Turn Your Intranet Into A Collaboration Platform
> http://p.sf.net/sfu/ExoPlatform
> _______________________________________________
> Maxima-discuss mailing list
> Max...@li...
> https://lists.sourceforge.net/lists/listinfo/maxima-discuss
>

Re: [Maxima-discuss] How to break out of a loop with a block?

[Barton W. <wi...@un...>]

For a workaround, see user documentation for  "catch" and "throw."

Re: [Maxima-discuss] How to break out of a loop with a block?

[Stavros M. <mac...@al...>]

I wouldn't call "catch" and "throw" *workarounds* for "return", which
implies that return is not functioning properly. I'd say that they are
complementary control operations.

              -s


On Sun, Apr 27, 2014 at 5:50 PM, Barton Willis <wi...@un...> wrote:

> For a workaround, see user documentation for  "catch" and "throw."
>
>
> ------------------------------------------------------------------------------
> Start Your Social Network Today - Download eXo Platform
> Build your Enterprise Intranet with eXo Platform Software
> Java Based Open Source Intranet - Social, Extensible, Cloud Ready
> Get Started Now And Turn Your Intranet Into A Collaboration Platform
> http://p.sf.net/sfu/ExoPlatform
> _______________________________________________
> Maxima-discuss mailing list
> Max...@li...
> https://lists.sourceforge.net/lists/listinfo/maxima-discuss
>

Re: [Maxima-discuss] How to break out of a loop with a block?

[Robert D. <rob...@gm...>]

On 2014-04-27, Barton Willis <wi...@un...> wrote:

> For a workaround, see user documentation for  "catch" and "throw."

Expanding on this suggestion, how about:

  foo (j) := catch (for i thru 10 do block (blah, blah, blah, if i=j then throw(i)));

  foo (5);
   => 5

  foo (20);
   => done

Note that throw/catch is a "nonlocal" mechanism -- 'throw' could be
buried within nested blocks or functions calls.

best

Robert Dodier