Boyko, your impression that 'cm' is an abbreviation for 'centimeter', used to denote the unit of length, is correct. Still it is an expression. Centi is one hundredth, 0.01, and 'meter' is an algebraic entity. Meter can be squared to give a unit of area, square meter, 'm²' . 'cm²' means square centimeter, (cm)². According to standard convention the square should be evaluated before the multiplication, so cm² should mean centi square meter, c(m²). School children has to accept that teachers don't adhere to their own rules.
Q. 'How exactly is it better'? A. It is without the above exception, and it is easily generalized to more operations than addition, multiplication, and exponentiation. Q. 'how does J convention lead to omitting parentheses'? A. The J convention allows a*(b+c) to be written a*b+c. The parentheses are omitted. Q. 'the precedences hardly present a problem'. A. Precedences present problems to the pupils even if it is no problem to you. - Bo >________________________________ > Fra: Boyko Bantchev <boyk...@gmail.com> >Til: programm...@jsoftware.com >Sendt: 16:21 søndag den 9. december 2012 >Emne: Re: [Jprogramming] J v Python > >On 9 December 2012 08:41, Bo Jacoby <bojac...@yahoo.dk> wrote: >> Well, 'cm' is a product, c*m, where c=.0.01 and m is a meter. > >All my life I have been under the impression that 'cm' is an >abbreviation for 'centimeter', used to denote the unit of length, >and not an arithmetic expression. And that, similarly, 'cm²' is >a denotation for a unit derived from 'cm', and does not include >operations. > >> The J convention is that expressions are evaluated from right to left: >> a*b+c means a*(b+c). > >How is J related to your treatment of 'cm' and 'cm²', and how does >J convention lead to 'omitting parentheses'? > >> It is better because is is simpler and more general. > >How exactly? >I agree that if you have many operations, not having precedences >between them is a plus. But in school algebra there are no many >operations, so the precedences hardly present a problem. And, let >us not forget that in J the evaluation does not occur in strictly >one direction. As for whether right-to-left is better than >left-to-right, I am not sure. I see advantages in both systems. >---------------------------------------------------------------------- >For information about J forums see http://www.jsoftware.com/forums.htm > > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
