Re: [Factor-talk] ndrop
Feel free to ask more questions on the mailing list, or through a Github Issue if you'd like some help. On Wed, Jan 28, 2015 at 7:48 AM, Alexander Iljin wrote: > Hello, Jon! > > Thank you, you've explained a lot! > > It's funny that I stumbled into this on my second day of > experimentation. Turns out there's an important characteristic of the > language, and thanks to you I'm now aware of it. Unfortunately, the > documentation is too terse for me to understand at this time, but I'll keep > trying. > > You've been very helpful! > > ---=--- > Александр > > > -- > Dive into the World of Parallel Programming. The Go Parallel Website, > sponsored by Intel and developed in partnership with Slashdot Media, is > your > hub for all things parallel software development, from weekly thought > leadership blogs to news, videos, case studies, tutorials and more. Take a > look and join the conversation now. http://goparallel.sourceforge.net/ > ___ > Factor-talk mailing list > Factor-talk@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/factor-talk > -- Dive into the World of Parallel Programming. The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/___ Factor-talk mailing list Factor-talk@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/factor-talk
Re: [Factor-talk] ndrop
Hello, Jon! Thank you, you've explained a lot! It's funny that I stumbled into this on my second day of experimentation. Turns out there's an important characteristic of the language, and thanks to you I'm now aware of it. Unfortunately, the documentation is too terse for me to understand at this time, but I'll keep trying. You've been very helpful! ---=--- Александр -- Dive into the World of Parallel Programming. The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/ ___ Factor-talk mailing list Factor-talk@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/factor-talk
Re: [Factor-talk] ndrop
Hi Alexander, The input quotations to “while” don't match their expected effects > Input Expected Got > [ dup 0 > ] ( ..a -- ..b ? ) ( x -- x x ) > [ 1 - swap drop ] ( ..b -- ..a ) ( x x -- x ) > > Regarding the first line: > These two lines can not be interpreted separately, as you'll se below. Input Expected Got > [ dup 0 > ] ( ..a -- ..b ? ) ( x -- x x ) > > I read it as "a boolean is expected at the stack top, but some other > value was found". The first line means "starting from a number of elements on the stack (represented as "..a"), there should be "..b" elements and a boolean on the stack. In your case, based on the "Got" column, it means ..a is 1 element, and ..b and the boolean are 2 elements (so ..b is 1 element). It doesn't say anything about the types of the elements. > How can that be if the last function is ">", and it does return a > boolean. > The error is not about the types of the elements (using '?' does mean the type should be a boolean, but it is just a convention). The two lines can't be read separately: quoting from the docs ( http://docs.factorcode.org/content/article-effects-variables.html) : "the number of inputs or outputs represented by a particular .. name must match among all of the quotations". So the error is about the fact that the second line forces "..b" to represent 2 elements, which contradicts the first line where ..b must represent 1 element. > I read it as "you can't reduce the stack size inside the loop body". > Why not? > Words must have a known fixed stack effect. This is a design decision. The number of inputs and outputs is fixed, must be declared and must match the result inferred from the body of the word. This is explained in http://docs.factorcode.org/content/article-cookbook.html and its linked articles (for example http://docs.factorcode.org/content/article-effects.html). However, there is some more advanced stuff to this: - Some flexibilty is allowed for inline words (see http://docs.factorcode.org/content/article-effects-variables.html) which allows them to have a stack effect depending on their inputs. Still the resulting stack effect must be fixed at each call site. - Also, ndrop already exists in the library: http://docs.factorcode.org/content/word-ndrop,generalizations.html The key to make it work is to use macros ( http://docs.factorcode.org/content/article-macros.html). "1 ndrop" is changed into "[ drop ] [ call ] keep drop", "2 ndrop" is changed into "[ drop ] [ call ] keep [ call ] keep drop", etc. You can see it by entering "[ drop ] 2 call-n" in the graphical listener and pressing CTRL-m. But this means the argument to ndrop must be a known at compile time so that the macro expansion succeeds. For example: : foo ( x x -- ) 1 1 + ndrop ; ! error, Cannot apply “call-n” to a run-time computed value : bar ( x x -- ) 2 ndrop ; ! OK Hope that helps, cheers, Jon -- Dive into the World of Parallel Programming. The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/___ Factor-talk mailing list Factor-talk@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/factor-talk
[Factor-talk] ndrop
Hi, all! I'm a newbie trying to understand Factor. Today I wrote a function called ndrop. The idea is that if you have nine pieces of junk on the stack you could write "9 ndrop" to get rid of them. Here's my attempted solution: USING: kernel math ; IN: ndrop ! Drop n items from the stack (plus the "n" itself). : ndrop ( ..n -- ) [ dup 0 > ] [ 1 - swap drop ] while drop ; When I try to run it I get some error messages that I need your help understanding: The word ndrop cannot be executed because it failed to compile The input quotations to “while” don't match their expected effects Input Expected Got [ dup 0 > ] ( ..a -- ..b ? ) ( x -- x x ) [ 1 - swap drop ] ( ..b -- ..a ) ( x x -- x ) Regarding the first line: Input Expected Got [ dup 0 > ] ( ..a -- ..b ? ) ( x -- x x ) I read it as "a boolean is expected at the stack top, but some other value was found". How can that be if the last function is ">", and it does return a boolean. Regarding the second line: Input Expected Got [ 1 - swap drop ] ( ..b -- ..a ) ( x x -- x ) I read it as "you can't reduce the stack size inside the loop body". Why not? Any general advice would be highly welcome as well. ---=--- Александр -- Dive into the World of Parallel Programming. The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/ ___ Factor-talk mailing list Factor-talk@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/factor-talk
