Space leak

From	Paul Rubin <no.email@nospam.invalid>
Newsgroups	comp.lang.haskell
Subject	Space leak
Date	2012-12-12 14:36 -0800
Organization	Nightsong/Fort GNOX
Message-ID	<7x1ueuhp8k.fsf@ruckus.brouhaha.com> (permalink)

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I had a space leak in a program that I distilled down to the following:

   main = print $ length (replicateM 15 "012")

This should generate all the 15-digit ternary numbers (with leading 0's)
so the length of the list is 3**15=14348907.  It gets that result
correctly, but uses almost a gigabyte of ram in computing it.

As an exercise I wrote my own version of the List datatype and the monad
instance for it doing the obvious things, and the same behavior
happened.  Writing a strict version of the length function using foldl1'
didn't help either.

It's not real obvious to me what's going on.  Is there a simple
explanation why replicateM doesn't generate values lazily that are
consumed by length?

Thanks.

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Thread

Space leak Paul Rubin <no.email@nospam.invalid> - 2012-12-12 14:36 -0800
  Re: Space leak Piotr Kalinowski <pitkali@gmail.com> - 2012-12-13 13:58 +0100
    Re: Space leak Paul Rubin <no.email@nospam.invalid> - 2012-12-13 08:40 -0800
      Re: Space leak Piotr Kalinowski <pitkali@gmail.com> - 2012-12-17 14:18 +0100
      Re: Space leak Wolfgang Ehrlich <wolfgang.ehrlich@googlemail.com> - 2013-01-08 06:15 -0800
        Re: Space leak Wolfgang Ehrlich <wolfgang.ehrlich@googlemail.com> - 2013-01-09 00:15 -0800
  Re: Space leak Dirk Thierbach <dthierbach@usenet.arcornews.de> - 2012-12-14 00:07 +0100
  Re: Space leak "Albert Y. C. Lai" <trebla@vex.net> - 2012-12-24 18:51 -0500

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