lazyio: Run IO actions lazily while respecting their order

[ bsd3, control, library, monads ] [ Propose Tags ]

Run IO actions lazily while respecting their order. Running a value of the LazyIO monad in the IO monad is like starting a thread which is however driven by its output. That is, the LazyIO action is only executed as far as necessary in order to provide the required data.

The package may help you to avoid stack overflows in mapM. Say you have

mapM f xs

where xs is a long list. When run, you may encounter a stack overflow. To prevent it, write instead:

import qualified System.IO.Lazy as LazyIO $ mapM (LazyIO.interleave . f) xs

The stack overflow is gone.




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Versions [RSS] 0.0.1, 0.0.2, 0.0.3,,,, 0.1,,,,
Change log CHANGES
Dependencies base (>=1.0 && <5), special-functors (>=1.0 && <1.1), transformers (>=0.2 && <0.7), unsafe (>=0.0 && <0.1) [details]
License BSD-3-Clause
Author Henning Thielemann <>
Maintainer Henning Thielemann <>
Revised Revision 1 made by HenningThielemann at 2023-02-16T12:04:34Z
Category Monads, Control
Home page
Source repo head: darcs get
this: darcs get --tag
Uploaded by HenningThielemann at 2016-12-14T21:16:25Z
Distributions LTSHaskell:, NixOS:, Stackage:
Reverse Dependencies 4 direct, 4 indirect [details]
Executables test
Downloads 8907 total (36 in the last 30 days)
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Status Docs available [build log]
Last success reported on 2016-12-14 [all 1 reports]