lazyio

Run IO actions lazily while respecting their order

http://www.haskell.org/haskellwiki/Lazy_IO

LTS Haskell 24.43:	0.1.0.4@rev:1
Stackage Nightly 2026-06-04:	0.1.0.6
Latest on Hackage:	0.1.0.6

See all snapshots lazyio appears in

BSD-3-Clause licensed and maintained by Henning Thielemann

This version can be pinned in stack with:lazyio-0.1.0.6@sha256:5107b645a118df275df8a1896dc443efae3b8bbe48093541217bd1711f3eee39,1925

Module documentation for 0.1.0.6

System
- System.IO
  - System.IO.Lazy

Depends on 3 packages(full list with versions):

base, transformers, unsafe

Used by 1 package in nightly-2026-06-04(full list with versions):

lapack

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

LazyIO.run $ mapM (LazyIO.interleave . f) xs

The stack overflow is gone.