BTW, Knuth did something else which typifies APL thinking. In a note or paper (I can not find it now), he argued strongly that 1=0^0, not undefined, not 0, not anything else. The common conventional statement of a polynomial, p(x)=sigma(k=0;k<=n) a[k]*x^k, requires that x^0 be 1. Some writers are aware of this dependency and, being careful, write instead the ugly p(x)=a[0]+sigma(k=1;k<=n)a[k]*x^k.
Attention to edge cases is typical of APL thinking. It's another way to stay in the world of expressions and away from the world of statements. You know: if k=0 then a[0] else a[k]*x^k endif On Wed, Jan 15, 2014 at 6:20 PM, Roger Hui <rogerhui.can...@gmail.com>wrote: > One aspect: J/APL programmers tend to stay in the nice world of > expressions and avoid the nastier world of statements. This tendency > pushes you towards array thinking and away from scalar thinking. > > For example, if b is a boolean array, and you want 4 where b is 0 and 17 > where b is 1, write: > > (4*0=b)+(17*1=b) > > And of course the signs of real numbers x are: > > (x>0)-(x<0) > > Even Knuth, an eminent mathematician and computer scientist but not an APL > programmer, knows to <strike>steal</strike> adopt this idea. See: Knuth, *Two > Notes on Notation* <http://arxiv.org/PS_cache/math/pdf/9205/9205211v1.pdf>, > 1992-05-01. In the first half of the paper he describes how "Iverson's > convention" can be used to simplify the statement and manipulation of sums. > > See also: > > http://www.jsoftware.com/papers/perlis77.htm > http://www.jsoftware.com/papers/perlis78.htm > http://www.jsoftware.com/papers/APLQA.htm#Perlis-foreword > > > > > > On Wed, Jan 15, 2014 at 5:32 PM, Joe Bogner <joebog...@gmail.com> wrote: > >> I went googling for some deeper material on how to think like an APL >> programmer. I have read/skimmed through a good set of the material on >> http://jsoftware.com/papers/ and have skimmed through many of the >> books listed on http://www.jsoftware.com/jwiki/Books. >> >> Are there any specific recommendations, free or for purchase? Or, >> perhaps I should spend more time with the list above. >> >> I found this, The APL Idiom List by Perlis and Rugaber, which looks >> similar to what I'm looking for: >> http://archive.vector.org.uk/resource/yaleidioms.pdf. >> >> The review of this book looks like what I'm after, >> >> http://www.amazon.com/Handbook-APL-programming-Clark-Wiedmann/dp/0884050262 >> , >> constructing useful programs and going into more depth. >> >> Or something of the style of The Little Schemer, >> http://scottn.us/downloads/The_Little_Schemer.pdf >> >> I searched the forum and had trouble finding a relevant post >> ---------------------------------------------------------------------- >> For information about J forums see http://www.jsoftware.com/forums.htm >> > > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
