[Haskell-cafe] Strictness in do block

John Goerzen jgoerzen at complete.org
Wed Jul 5 07:04:22 EDT 2006


One thing that seems to keep biting me is strictness in do blocks.

What I want to know is the generic way to force an entire String (or
other list, perhaps from hGetContents) to be evaluated (read into RAM, I
guess) so the underlying file can be closed.... and do it right now.

One quick hack that works is hPutStrLn on it, right where I want it to
be evaluated.  But ugly and not always appropriate.  Passing it to some
other IO-based functions also works, but again, that doesn't "feel"

I can always stumble upon things that work, but I'm never sure if I've
got 'em right.  So, what is the idiomatic way to do this?

Most of the documents I see out there on this topic are for usage
outside the I/O monad, and I'm not seeing how they apply here.


-- John

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