What it means is that the value returned by gen/return can't be shrunk. Shrinking is done by constructing a (lazily evaluated) tree of "smaller" forms of the same thing. So a number, let's say 4, contains a tree of smaller numbers (0, 1, 2, and 3) which specify how to shrink it. (The tree is constructed in an intelligent way to make shrinking more efficient than "try everything".) When you use gen/return you don't have any of that context, so the returned value cannot be shrunk.
This situation is a bit more complex when you use gen/bind, though, because the result of the gen/bind call "inherits" a shrink tree from the generator given to gen/bind. That's why my function can shrink despite using gen/return for its final value. The gen/return isn't shrinking, but the gen/bind is. Carlo On 15 August 2015 at 02:49, Mayank Jain <firesof...@gmail.com> wrote: > Ah right! I knew I had to use gen/choose for this, > I am still grokking bind :) > > Thanks for your help! > That indeed did the trick for me :) > > One thing I am clear about is, > If I use gen/return it says it'll not shrink. > Does that mean when a test fails for a certain order, it won't try to > shrink that order of collection? > Because I have used a gen/return at the end of the generator? > > Thanks again for your help! :) > > On Fri, Aug 14, 2015 at 8:13 PM, Carlo Zancanaro <carlozancan...@gmail.com > > wrote: > >> Hey Mayank! >> >> Similarly to your attempt last time, you need to use gen/bind to get the >> result of a generator which you can then use to make a new generator. >> >> (defn- rand-interleave* [coll acc] >> (if (seq coll) >> (gen/bind (gen/choose 0 (dec (count coll))) >> (fn [index] >> (let [value (first (get coll index)) >> coll (->> (update-in coll [index] next) >> (remove empty?) >> vec)] >> (rand-interleave* coll (conj acc value))))) >> (gen/return acc))) >> >> (defn rand-interleave [& colls] >> (rand-interleave* (vec colls) [])) >> >> The (gen/choose 0 (dec (count coll))) is similar to your rand-count >> function, then the generated number is passed to the function as result. >> Writing it this way will shrink towards the (apply concat args) (ie. as >> it shrinks it will move towards just concatenating the arguments). >> >> In terms of the recursion: this will eventually overflow the stack. I >> don't know of a way to trampoline generators, so I don't know how to avoid >> that. (This is a bit of a recurring problem with monadic code in Clojure, I >> feel, as algo.monads had a similar problem last time I checked.) For the >> moment I'm just ignoring this theoretical problem until it becomes a >> practical problem. >> >> I hope that helps! >> >> Carlo >> >> On 14 August 2015 at 23:39, Mayank Jain <firesof...@gmail.com> wrote: >> >>> Hi Everyone, >>> >>> Here's the problem I am facing, >>> I need to write a generator which takes any number of sequences, >>> interleaves them but maintains the order within each sequence. >>> Assume each sequence has at least one element. >>> >>> For example: >>> >>> (rand-interleave [1 2 3 4] [:a :b] [:A :B :C :D :E]) >>>> => [:a 1 2 :b :A :B :C 3 :D 4 :E] >>> >>> >>> (rand-interleave [1 2 3 4]) >>>> => [1 2 3 4] >>> >>> >>> (rand-interleave [1]) >>>> => [1] >>> >>> >>> (rand-interleave [1] [:a] [:A]) >>>> => [:a 1 :A] >>> >>> >>> I have been able to write this down as clojure functions. >>> But I am unable to convert this into a test.check generator. >>> >>> Specifically: >>> >>> - How to pass random index count without using rand-int i.e. use >>> gen/choose >>> - How do I write recursive functions which play well with test.check >>> >>> Here's my take on it (without the generators). >>> >>> (defn- first-nth >>>> "(first-nth [[1 2 3 4] [:a :b :c :d]] >>>> 1) >>>> => :a" >>>> [coll n] >>>> (first (nth coll n))) >>> >>> >>> >>> (defn- next-nth >>>> "(next-nth [[1 2 3 4] [:a :b :c :d]] >>>> 1) >>>> => [[1 2 3 4] (:b :c :d)]" >>>> [coll n] >>>> (->> n >>>> (nth coll) >>>> next >>>> (assoc coll n) >>>> (remove nil?) >>>> vec)) >>> >>> >>> >>> (defn- rand-count >>>> [coll] >>>> (rand-int (count coll))) >>> >>> >>> >>> (defn- rand-interleave* >>>> [coll acc] >>>> (let [n (rand-count coll)] >>>> (if (not-empty coll) >>>> (rand-interleave* (next-nth coll n) >>>> (conj acc >>>> (first-nth coll n))) >>>> acc))) >>> >>> >>> >>> (defn rand-interleave >>>> [& args] >>>> ;; Make args a vector as I would like to >>>> ;; look up elements by their index values. >>>> (rand-interleave* (vec args) [])) >>> >>> >>> Looking forward to any suggestions on how to solve it :) >>> >>> Thanks, >>> Mayank. >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "Clojure" group. >>> To post to this group, send email to clojure@googlegroups.com >>> Note that posts from new members are moderated - please be patient with >>> your first post. >>> To unsubscribe from this group, send email to >>> clojure+unsubscr...@googlegroups.com >>> For more options, visit this group at >>> http://groups.google.com/group/clojure?hl=en >>> --- >>> You received this message because you are subscribed to the Google >>> Groups "Clojure" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to clojure+unsubscr...@googlegroups.com. >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> -- >> You received this message because you are subscribed to the Google >> Groups "Clojure" group. >> To post to this group, send email to clojure@googlegroups.com >> Note that posts from new members are moderated - please be patient with >> your first post. >> To unsubscribe from this group, send email to >> clojure+unsubscr...@googlegroups.com >> For more options, visit this group at >> http://groups.google.com/group/clojure?hl=en >> --- >> You received this message because you are subscribed to the Google Groups >> "Clojure" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to clojure+unsubscr...@googlegroups.com. >> For more options, visit https://groups.google.com/d/optout. >> > > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clojure@googlegroups.com > Note that posts from new members are moderated - please be patient with > your first post. > To unsubscribe from this group, send email to > clojure+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en > --- > You received this message because you are subscribed to the Google Groups > "Clojure" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to clojure+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Clojure" group. 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