The lazyio package

[ Tags: 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.


Versions 0.0.1, 0.0.2, 0.0.3,,,, 0.1,,,,
Change log CHANGES
Dependencies base (>=1.0 && <5), special-functors (==1.0.*), transformers (>=0.2 && <0.6), unsafe (==0.0.*) [details]
License BSD3
Author Henning Thielemann <>
Maintainer Henning Thielemann <>
Category Monads, Control
Home page
Source repository head: darcs get
this: darcs get --tag
Uploaded Wed Dec 14 21:16:25 UTC 2016 by HenningThielemann
Distributions LTSHaskell:, NixOS:, Stackage:, Tumbleweed:
Executables test
Downloads 1931 total (16 in the last 30 days)
Rating 0.0 (0 ratings) [clear rating]
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Status Docs available [build log]
Last success reported on 2016-12-14 [all 1 reports]
Hackage Matrix CI





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