On Fri, Apr 23, 2010 at 10:15 AM, bb <bblo...@arcor.de> wrote: > Simon King schrieb: > > Hi! >> >> On Apr 23, 2:05 pm, bb <bblo...@arcor.de> wrote: >> >> >>> ... >>> The second passage I found was at >>> >>> http://www.sagemath.org/doc/tutorial/programming.html >>> >>> ... When comparing objects of different types in Sage, in most cases >>> Sage tries to find a canonical coercion of both objects to a common >>> parent. >>> >>> >> >> I am translating the whole tutorial, so, you are right with both >> passages you mention. IIRC there was a number of questions on sage- >> support about coercion (understandably, I think). But the tutorial and >> the "Sage constructions" don't seem to address it. Therefore I >> consider to add a new section on conversion vs. coercion in tutorial/ >> programming (in English as well), apart from just translating. >> >> The notions of type conversion (in C), conversion (in Sage) and >> coercion (in Sage) are distinct, but have a big semantic overlap. >> "Being distinct and having a semantic overlap" means: One has to be >> particularly careful in choosing sound notions in translation, or >> confusion will rise. >> >> Examples: >> 1) In C: >> int i = 10; >> char j; >> j = (char)i; // type conversion >> >> > cast: > Sorry, I only see that from a perspective of computer science/programming. > The conversion in the example above is called "explicit type conversion". > That is done by "casting". In your example you used a C-like casting: > (char)i;. In C++ there is also a functional casting possible: char (i) - > may be its possible in newer C versions as well? And you assign that to a > proper variable j. That is the way in strong-typed languages. If you try > i=(char) i; you should get an error message. Very often people do not > understand, that in the cast process the original type of the casted > variable will be preserved! i is integer before and after casting! > > I know a lot of C literature and do not know any one calling any form of > type conversion coercion! Because there is no implicit conversion in > strong-typed languages possible. (Well, there are exceptions, i. e. > short a=2000; > int b; > b=a; > and in printing with printf() by format code. That only holds, because you > can always fit a short in an int, but the opposite is not true, and it is > also not true for many other data types (see a C reference!).) > sage: i=2000 > sage: float(i) > 2000.0 > sage: i > 2000 > sage: f=23.34 > sage: f > 23.3400000000000 > sage: int (f) > 23 > sage: f > 23.3400000000000 > sage: > > > > coercion: > is an implicit type conversion. Python/Sage are not strong-typed languages! >
Actually, Python *is* strongly typed. Instead of trying to explain the meaning of terms such as "strongly typed", "dynamically typed", etc. I refer the reader to Wikipedia [1]. -- William [1] http://en.wikipedia.org/wiki/Python_(programming_language) -- To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org
