I have tried to use an implementation of mini-kanren in clojure. But been struggling to understand the difference between cond-a cond-u and cond-e. I seem to be quite clear about cond-e but understanding of cond-a and cond-u is quiet bad.
cond-e takes a set of goals and then tries each of them... i.e tries all the branches that succeed.
cond-a and cond-u on the contrary commit to the branch whose first predicate succeeds and cond-a returns all the possible successful unifications there after. while cond-u returns only the first successfull unification ... but however it seems like this understanding is not correct when I use it. Can somebody help me clarify this understanding.
cond-e gives every answer from all branches that succeed
cond-i gives every answer but interleaves them.
cond-a only gives the answers from the first successful branch
cond-u only gives the first answer from the first successful branch
I was just trying to get my head around these matters. There's a shortified scheme implementation Sokuza-kanren with a few comments, I'll read it tonight.
来源：https://stackoverflow.com/questions/4112996/mini-kanren-what-is-the-difference-between-cond-a-cond-u-and-cond-e