[Haskell-cafe] How can we detect and fix memory leak due to lazyness?

Thomas Conway drtomc at gmail.com
Mon Aug 7 21:35:01 EDT 2006

> Perhaps your instances will work correctly with this data declaration?

Perhaps it might.  But that misses an important point.

The biggest impediment to developing large robust applications with
Haskell is the opacity of its performance model.  Haskell is fantastic
in very many ways, but this is a really serious difficulty.  I can
make a seemingly slight change to my program and the performance
changes dramatically.  What's worse, the connection between the cause
of the blowup and place where it is observed can often be quite

There's a classic example of two one line haskell programs, one of
which uses O(1) stack space and the other O(n) stack space, even
though they compute the same result, and which are so similar, you
have to stare at them for five minutes before you can spot the

Hughes' "Why functional programming matters" argues [rightly] that
lazy FP provides a better "glue", to allow greater abstraction at the
semantic level.  The flip side, which IIRC, he doesn't mention is the
opacity of the performance model.

Here's a question for the experts.  What generalizations can I make
about the performance of lazy functions under composition? In
particular, if all my individual functions are well behaved, will the
program as a whole be well behaved?

[*] Gosh, this is beginning to sound like a diatribe on the evils of
pointers and manual memory management in C. Interesting....

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