I had a very short look at Roger's Sudoku solver http://www.jsoftware.com/jwiki/Essays/Sudoku
I made a sudoku solver some years ago, in Pascal, before I knew J. The sudoku was represented by an array of shape 3 3 3 3 rather than of shape 9 9. This has the advantage that not only rows and columns, but also the boxes, are represented as sub-arrays. >________________________________ > Fra: Graham Parkhouse <graham.parkho...@ntlworld.com> >Til: programm...@jsoftware.com >Sendt: 0:49 torsdag den 31. januar 2013 >Emne: [Jprogramming] Explicit v tacit > >Kip Murray wrote: > >Message: 6 >Date: Fri, 25 Jan 2013 20:31:56 -0600 >From: km <k...@math.uh.edu> >To: "programm...@jsoftware.com" <programm...@jsoftware.com> >Subject: Re: [Jprogramming] applying >1 gerunds to a set of items >Message-ID: <eb35aa7d-a7d9-4f51-b885-624b78c52...@math.uh.edu> >Content-Type: text/plain; charset=utf-8 > >Dan, most of the code in the z locale is explicit. What is the fundamental >value of explicit code? > >------------------------------- > >I have been studying Roger's Sudoku solver > >http://www.jsoftware.com/jwiki/Essays/Sudoku > >after attempting my own solver. Mine was going OK, on the very easy >problems, but, even with guessing, it ground to a standstill on a supposedly >not very difficult one. So, rather than soldier on I studied Roger's code, >and learned a lot. His use of nub sieve (~:) to check the uniqueness of >numbers within regions was beautiful. Now that I'm impressed by the >usefulness of this primitive, I hope I shall use it appropriately in the >future. > >It seems to me that Roger used tacit code where practicable. He used the >rank conjunction judiciously. The 'main' function, sudoku, is a one-liner of >immense beauty, embodying two mighty loops and comprehensive stack >management in 11 words. By adding @ , to the end of the sentence he blocks >the possibility of solving any number of Sudoku puzzles at once! Had he left >them off, the right argument could have been a matrix of n problems, with >shape n by 81. > >I have gleaned from this forum that it is generally better, efficiency-wise, >for explicit verbs to have large rank. If the arguments have much higher >rank than the verb, the frame is big, and the verb has to be interpreted >many times each single time it is called. Am I right in thinking that this >is not the case for tacit code? Doesn't the tacit code get interpreted once, >when the script is loaded? If this is so there are many situations where >tacit code is considerably quicker in execution than the equivalent explicit >code. > >I was severely challenged by tacit code when I first moved to J from APL. I >used to think in terms of nouns, visualising the characteristics of the data >as it was transformed by each step of the calculation. I was happy to >'write' functions and give them names, but to have one-liner assignments to >verbs instead of nouns as my preferred way of thinking, has taken years. >Roger has a one-liner for the verb ok. My old mindset would reserve ok as >the name for a noun, and it would be either 0 or 1! Notice how much more >content there is in a verb ok that returns 0 or 1, content that doesn't vary >with the data. > >Thank you, all, for the experience. > >Graham > > >---------------------------------------------------------------------- >For information about J forums see http://www.jsoftware.com/forums.htm > > > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
