ClassCastException on second pass of loop, works fine during the first.

[Sean Chalmers]

Greetings ! 

I'm attempting to implement Othello in Clojure and I've run into a problem when actually running my game loop. On the first run through, everything works as expected, the black player can make their move, the board is updated and everything is awesome. However when the program loops and it is the white players turn, after they have entered their move the program crashes with the stacktrace at the bottom of this message.. 

I seem to be having a brain fuzz moment because I can't see how much application would complete happily the first time through without error, then when the nearly identical steps are taken for turn two, I seem to have a type error. The code is here: https://github.com/mankyKitty/clojure-othello/blob/master/src/othello/core.clj . I know it's not great, work in progress! :)

From what I can tell from the ST the error is from my "squares-to-flip" function but I'm unable to reproduce the results in the repl, and I've yet to reach the point where I'm adding a print on every second line (though I'm close). 

I had originally deduced it was the 'merge' call on the times I would have an empty second argument, hence the 'if' in there but that doesn't appear to have helped at all.

I assume it's something I've not anticipated or accounted for with respect to my loop, but I'm not quite sure.. 

Thanks in advance !

--- STACKTRACE ---

Exception in thread "main" java.lang.ClassCastException: clojure.lang.PersistentHashMap cannot be cast to java.util.Map$Entry

at clojure.lang.APersistentMap.cons(APersistentMap.java:42)

at clojure.lang.RT.conj(RT.java:562)

at clojure.core$conj.invoke(core.clj:83)

at clojure.core$merge$fn__4275.invoke(core.clj:2684)

at clojure.core$reduce1.invoke(core.clj:896)

at clojure.core$reduce1.invoke(core.clj:887)

at clojure.core$merge.doInvoke(core.clj:2684)

at clojure.lang.RestFn.invoke(RestFn.java:421)

at othello.core$squares_to_flip.invoke(core.clj:186)

at othello.core$game_loop.invoke(core.clj:213)

at othello.core$_main.doInvoke(core.clj:225)

at clojure.lang.RestFn.invoke(RestFn.java:397)

at clojure.lang.Var.invoke(Var.java:411)

at user$eval5$fn__7.invoke(form-init5981136443637675542.clj:1)

at user$eval5.invoke(form-init5981136443637675542.clj:1)

at clojure.lang.Compiler.eval(Compiler.java:6619)

at clojure.lang.Compiler.eval(Compiler.java:6609)

at clojure.lang.Compiler.load(Compiler.java:7064)

at clojure.lang.Compiler.loadFile(Compiler.java:7020)

at clojure.main$load_script.invoke(main.clj:294)

at clojure.main$init_opt.invoke(main.clj:299)

at clojure.main$initialize.invoke(main.clj:327)

at clojure.main$null_opt.invoke(main.clj:362)

at clojure.main$main.doInvoke(main.clj:440)

at clojure.lang.RestFn.invoke(RestFn.java:421)

at clojure.lang.Var.invoke(Var.java:419)

at clojure.lang.AFn.applyToHelper(AFn.java:163)

at clojure.lang.Var.applyTo(Var.java:532)

at clojure.main.main(main.java:37)

[Alex Miller]

I would expect others to be either nil or a non-empty seq (never empty) but empty? will return true on a nil, so that still works. I would have swapped the cases and used seq as the test.

However, without really reading this too closely, I'd guess the real problem is that you want to (apply merge fst others) since others is a seq of maps.

[Sean Chalmers]

Hrmm, I'll give that a try and see what I come up with. Thanks for the pointer about others, that makes sense. ><!

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