accumulator

Should I avoid tail recursion in Prolog and in general?

寵の児 提交于 2019-11-27 09:40:46
I'm working through "Learn Prolog now" online book for fun. I'm trying to write a predicate that goes through each member of a list and adds one to it, using accumulators. I have already done it easily without tail recursion. addone([],[]). addone([X|Xs],[Y|Ys]) :- Y is X+1, addone(Xs,Ys). But I have read that it is better to avoid this type of recursion for performance reasons. Is this true? Is it considered 'good practice' to use tail recursion always? Will it be worth the effort to use accumulators to get into a good habit? I have tried to change this example into using accumulators, but it

Should I avoid tail recursion in Prolog and in general?

回眸只為那壹抹淺笑 提交于 2019-11-26 14:48:37
问题 I'm working through "Learn Prolog now" online book for fun. I'm trying to write a predicate that goes through each member of a list and adds one to it, using accumulators. I have already done it easily without tail recursion. addone([],[]). addone([X|Xs],[Y|Ys]) :- Y is X+1, addone(Xs,Ys). But I have read that it is better to avoid this type of recursion for performance reasons. Is this true? Is it considered 'good practice' to use tail recursion always? Will it be worth the effort to use

Spark losing println() on stdout

假如想象 提交于 2019-11-26 06:44:57
问题 I have the following code: val blueCount = sc.accumulator[Long](0) val output = input.map { data => for (value <- data.getValues()) { if (record.getEnum() == DataEnum.BLUE) { blueCount += 1 println(\"Enum = BLUE : \" + value.toString() } } data }.persist(StorageLevel.MEMORY_ONLY_SER) output.saveAsTextFile(\"myOutput\") Then the blueCount is not zero, but I got no println() output! Am I missing anything here? Thanks! 回答1: This is a conceptual question... Imagine You have a big cluster,

Prolog Accumulators. Are they really a “different” concept?

橙三吉。 提交于 2019-11-26 00:55:53
问题 I am learning Prolog under my Artificial Intelligence Lab, from the source Learn Prolog Now!. In the 5th Chapter we come to learn about Accumulators . And as an example, these two code snippets are given. To Find the Length of a List without accumulators : len([],0). len([_|T],N) :- len(T,X), N is X+1. with accumulators : accLen([_|T],A,L) :- Anew is A+1, accLen(T,Anew,L). accLen([],A,A). I am unable to understand, how the two snippets are conceptually different? What exactly an accumulator