Re: (doseq/lazy/interop)? problem, different behaviour when adding a println

[Leon Grapenthin]

Hi Lucas,
 lazy sequences, as the one produced by the map/filter construct, aren't 
realized at once. I. e. they are returned as a sequence, but your map and 
filter lambdas are only invoked once somebody looks at whats in the 
sequence. Usually, steps are evaluated in chunks of size 32.

Your filter lambda is depending on mutable Java map.

When you count a lazy sequence, all elements are realized. 

So depending on whether you invoke count, the lambda will be invoked with a 
different version of the Java map.

You should solve this by eliminating the mutable state Java map - it makes 
your filter lambda impure. Lazy evaluation does not work with impure 
functions.

I'd recommend to learn about reduce, which will help you to write this much 
more concisely.

Kind regards, 
 Leon.

On Saturday, April 22, 2017 at 2:41:09 PM UTC+2, Lucas Wiener wrote:
>
> Hi all,
>
> I'm working on solving the problem http://adventofcode.com/2016/day/11 , 
> and ran into some weird behaviour. I have solved the actual problem, so 
> let's not focus on it.
>
> Here's my code:
>
> (defn compute3
>   {:test (fn []
>(is= (compute3 (create-state "F4 .  .  .  .  .  "
> "F3 .  .  .  LG .  "
> "F2 .  HG .  .  .  "
> "F1 E  .  HM .  LM "))
> 11))}
>   [state]
>   (let [done-simple-state (state->simple-state (construct-finished-state 
> state))
> inner-fn (fn [states steps java-memory-map]
>(println "On step" steps)
>(println "Number of states" (count states))
>(let [next-states (->> states
>   (map (fn [state]
>  (->> (get-next-states 
> state)
>   (filter (fn [s] 
> (nil? (.get java-memory-map (state->simple-state s
>   (flatten))]
>  ;; (println (count next-states)) <- Uncomment this 
> line to change the behavior
>  (if (.get java-memory-map done-simple-state)
>steps
>(do (doseq [next-state next-states]
>  (.put java-memory-map (state->simple-state 
> next-state) steps))
>(recur next-states (inc steps) 
> java-memory-map)]
> (inner-fn [state] 0 (java.util.HashMap.
>
> When running this in the repl I get the following output:
>
> On step 0
> Number of states 1
> On step 1
> Number of states 1
> On step 2
> Number of states 3
> On step 3
> Number of states 11
> On step 4
> Number of states 14
> On step 5
> Number of states 22
> On step 6
> Number of states 37
> On step 7
> Number of states 48
> On step 8
> Number of states 35
> On step 9
> Number of states 22
> On step 10
> Number of states 17
> On step 11
> Number of states 7
>
> However, if I uncomment the println statement I get the following output 
> in the REPL:
>
> On step 0
> Number of states 1
> 1
> On step 1
> Number of states 1
> 3
> On step 2
> Number of states 3
> 11
> On step 3
> Number of states 11
> 15
> On step 4
> Number of states 15
> 28
> On step 5
> Number of states 28
> 63
> On step 6
> Number of states 63
> 107
> On step 7
> Number of states 107
> 90
> On step 8
> Number of states 90
> 82
> On step 9
> Number of states 82
> 115
> On step 10
> Number of states 115
> 81
> On step 11
> Number of states 81
> 110
>
> Please note that "On step 4" prints "Number of states 14" and "Number of 
> states 15"  differently.
>
> Any thoughts?
>

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Re: (doseq/lazy/interop)? problem, different behaviour when adding a println

[Alan Thompson]

Unless prevented by outside considerations, it might also be
cleaner/simpler to copy all inputs from Java -> Clojure, do all the
algorithm work in Clojure, then copy all outputs back from Clojure -> Java.
I'm looking specifically at `java-memory-map`, but would also replace
native java stuff like `java.util.HashMap` with Clojure versions whenever
possible.  Again, the goal is to avoid clashes in the hidden assumptions of
the two models.
Alan

On Mon, Apr 24, 2017 at 1:05 PM, Alan Thompson  wrote:

> Having not gone through your code in detail, I would suggest replacing
> `map` -> `mapv` to make it an eager operation so that state updates (i.e. `
> next-states`) occur right away.  The presence of laziness where it is not
> needed or expected (especially in Java interop code) can cause problems
> with the (implicit) assumptions of other code.
> Alan
>
> On Sat, Apr 22, 2017 at 2:59 AM, Lucas Wiener  wrote:
>
>> Hi all,
>>
>> I'm working on solving the problem http://adventofcode.com/2016/day/11 ,
>> and ran into some weird behaviour. I have solved the actual problem, so
>> let's not focus on it.
>>
>> Here's my code:
>>
>> (defn compute3
>>   {:test (fn []
>>(is= (compute3 (create-state "F4 .  .  .  .  .  "
>> "F3 .  .  .  LG .  "
>> "F2 .  HG .  .  .  "
>> "F1 E  .  HM .  LM "))
>> 11))}
>>   [state]
>>   (let [done-simple-state (state->simple-state (construct-finished-state
>> state))
>> inner-fn (fn [states steps java-memory-map]
>>(println "On step" steps)
>>(println "Number of states" (count states))
>>(let [next-states (->> states
>>   (map (fn [state]
>>  (->> (get-next-states
>> state)
>>   (filter (fn [s]
>> (nil? (.get java-memory-map (state->simple-state s
>>   (flatten))]
>>  ;; (println (count next-states)) <- Uncomment this
>> line to change the behavior
>>  (if (.get java-memory-map done-simple-state)
>>steps
>>(do (doseq [next-state next-states]
>>  (.put java-memory-map (state->simple-state
>> next-state) steps))
>>(recur next-states (inc steps)
>> java-memory-map)]
>> (inner-fn [state] 0 (java.util.HashMap.
>>
>> When running this in the repl I get the following output:
>>
>> On step 0
>> Number of states 1
>> On step 1
>> Number of states 1
>> On step 2
>> Number of states 3
>> On step 3
>> Number of states 11
>> On step 4
>> Number of states 14
>> On step 5
>> Number of states 22
>> On step 6
>> Number of states 37
>> On step 7
>> Number of states 48
>> On step 8
>> Number of states 35
>> On step 9
>> Number of states 22
>> On step 10
>> Number of states 17
>> On step 11
>> Number of states 7
>>
>> However, if I uncomment the println statement I get the following output
>> in the REPL:
>>
>> On step 0
>> Number of states 1
>> 1
>> On step 1
>> Number of states 1
>> 3
>> On step 2
>> Number of states 3
>> 11
>> On step 3
>> Number of states 11
>> 15
>> On step 4
>> Number of states 15
>> 28
>> On step 5
>> Number of states 28
>> 63
>> On step 6
>> Number of states 63
>> 107
>> On step 7
>> Number of states 107
>> 90
>> On step 8
>> Number of states 90
>> 82
>> On step 9
>> Number of states 82
>> 115
>> On step 10
>> Number of states 115
>> 81
>> On step 11
>> Number of states 81
>> 110
>>
>> Please note that "On step 4" prints "Number of states 14" and "Number of
>> states 15"  differently.
>>
>> Any thoughts?
>>
>> --
>> 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.
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>>
>
>

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Re: (doseq/lazy/interop)? problem, different behaviour when adding a println

[Alan Thompson]

Having not gone through your code in detail, I would suggest replacing
`map` -> `mapv` to make it an eager operation so that state updates (i.e. `
next-states`) occur right away.  The presence of laziness where it is not
needed or expected (especially in Java interop code) can cause problems
with the (implicit) assumptions of other code.
Alan

On Sat, Apr 22, 2017 at 2:59 AM, Lucas Wiener  wrote:

> Hi all,
>
> I'm working on solving the problem http://adventofcode.com/2016/day/11 ,
> and ran into some weird behaviour. I have solved the actual problem, so
> let's not focus on it.
>
> Here's my code:
>
> (defn compute3
>   {:test (fn []
>(is= (compute3 (create-state "F4 .  .  .  .  .  "
> "F3 .  .  .  LG .  "
> "F2 .  HG .  .  .  "
> "F1 E  .  HM .  LM "))
> 11))}
>   [state]
>   (let [done-simple-state (state->simple-state (construct-finished-state
> state))
> inner-fn (fn [states steps java-memory-map]
>(println "On step" steps)
>(println "Number of states" (count states))
>(let [next-states (->> states
>   (map (fn [state]
>  (->> (get-next-states
> state)
>   (filter (fn [s]
> (nil? (.get java-memory-map (state->simple-state s
>   (flatten))]
>  ;; (println (count next-states)) <- Uncomment this
> line to change the behavior
>  (if (.get java-memory-map done-simple-state)
>steps
>(do (doseq [next-state next-states]
>  (.put java-memory-map (state->simple-state
> next-state) steps))
>(recur next-states (inc steps)
> java-memory-map)]
> (inner-fn [state] 0 (java.util.HashMap.
>
> When running this in the repl I get the following output:
>
> On step 0
> Number of states 1
> On step 1
> Number of states 1
> On step 2
> Number of states 3
> On step 3
> Number of states 11
> On step 4
> Number of states 14
> On step 5
> Number of states 22
> On step 6
> Number of states 37
> On step 7
> Number of states 48
> On step 8
> Number of states 35
> On step 9
> Number of states 22
> On step 10
> Number of states 17
> On step 11
> Number of states 7
>
> However, if I uncomment the println statement I get the following output
> in the REPL:
>
> On step 0
> Number of states 1
> 1
> On step 1
> Number of states 1
> 3
> On step 2
> Number of states 3
> 11
> On step 3
> Number of states 11
> 15
> On step 4
> Number of states 15
> 28
> On step 5
> Number of states 28
> 63
> On step 6
> Number of states 63
> 107
> On step 7
> Number of states 107
> 90
> On step 8
> Number of states 90
> 82
> On step 9
> Number of states 82
> 115
> On step 10
> Number of states 115
> 81
> On step 11
> Number of states 81
> 110
>
> Please note that "On step 4" prints "Number of states 14" and "Number of
> states 15"  differently.
>
> Any thoughts?
>
> --
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(doseq/lazy/interop)? problem, different behaviour when adding a println

[Lucas Wiener]

Hi all,

I'm working on solving the problem http://adventofcode.com/2016/day/11 , 
and ran into some weird behaviour. I have solved the actual problem, so 
let's not focus on it.

Here's my code:

(defn compute3
  {:test (fn []
   (is= (compute3 (create-state "F4 .  .  .  .  .  "
"F3 .  .  .  LG .  "
"F2 .  HG .  .  .  "
"F1 E  .  HM .  LM "))
11))}
  [state]
  (let [done-simple-state (state->simple-state (construct-finished-state 
state))
inner-fn (fn [states steps java-memory-map]
   (println "On step" steps)
   (println "Number of states" (count states))
   (let [next-states (->> states
  (map (fn [state]
 (->> (get-next-states 
state)
  (filter (fn [s] (nil? 
(.get java-memory-map (state->simple-state s
  (flatten))]
 ;; (println (count next-states)) <- Uncomment this 
line to change the behavior
 (if (.get java-memory-map done-simple-state)
   steps
   (do (doseq [next-state next-states]
 (.put java-memory-map (state->simple-state 
next-state) steps))
   (recur next-states (inc steps) 
java-memory-map)]
(inner-fn [state] 0 (java.util.HashMap.

When running this in the repl I get the following output:

On step 0
Number of states 1
On step 1
Number of states 1
On step 2
Number of states 3
On step 3
Number of states 11
On step 4
Number of states 14
On step 5
Number of states 22
On step 6
Number of states 37
On step 7
Number of states 48
On step 8
Number of states 35
On step 9
Number of states 22
On step 10
Number of states 17
On step 11
Number of states 7

However, if I uncomment the println statement I get the following output in 
the REPL:

On step 0
Number of states 1
1
On step 1
Number of states 1
3
On step 2
Number of states 3
11
On step 3
Number of states 11
15
On step 4
Number of states 15
28
On step 5
Number of states 28
63
On step 6
Number of states 63
107
On step 7
Number of states 107
90
On step 8
Number of states 90
82
On step 9
Number of states 82
115
On step 10
Number of states 115
81
On step 11
Number of states 81
110

Please note that "On step 4" prints "Number of states 14" and "Number of 
states 15"  differently.

Any thoughts?

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