ipc - Interactive Process Communication in Haskell -

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i trying write haskell program executes interactive program (also written in haskell), sending , receiving lines of text. interactive program reads stdin , writes stdout using standard haskell library.

however, proved more complicated anticipated, due haskell lazyness or other misterious thing happening on background. program apparently goes deadlock, , not receive line of text expected receive. receive text fine if interactive program terminates result of sending line of text, need program keep running , receive more data (it's called interactive reason). prints expected output after kill program receiving message. code looks this:

main =     (hin,hout,herr,pl) <- (runinteractivecommand "./playermain")     hsetbinarymode hin false     hsetbinarymode hout false     hsetbuffering hin linebuffering     hsetbuffering hout nobuffering     hputstr hin "start\n"     out <- hgetline hout     putstrln out

i tried replacing lazy strings strict data.text, behaviour same. light?

maybe reason output of ./playermain being buffered. ./playermain writes doesn't flushed right away, , hangs because keeps expecting more input.

that explain why do message when program terminates.

so maybe work if modify ./playermain , set stdout nobuffering.


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