# Using unsafePerformIO safely?

**URL:** <https://discourse.haskell.org/t/using-unsafeperformio-safely/4146>\
**Category:** Uncategorized\
**Created:** [February 28, 2022, 2:41pm UTC](https://discourse.haskell.org/t/using-unsafeperformio-safely/4146 "2022-02-28T14:41:23Z")\
**Posts on this page:** 1\
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**Author:** ![tomjaguarpaw](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/tomjaguarpaw/32/1230_2.png) [@tomjaguarpaw](https://discourse.haskell.org/u/tomjaguarpaw)\
**Post date:** [March 1, 2022, 6:51pm UTC](https://discourse.haskell.org/t/using-unsafeperformio-safely/4146/16 "2022-03-01T18:51:52Z")

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Here’s a concrete example of why I don’t like pretending that anything that interacts with the OS is “pure”:

At work we have a Nix-based build system. It “should be” pure, since Nix is reproducible. However, it sometimes calls out to external hardware which is transiently broken, caching “hardware did not respond” into our build results, and with no way of purging it. There’s no _direct_ analogue of that in Haskell, but it really makes me cautious of “pure” APIs that call out to the OS, and I wouldn’t use one myself, in practice. (I think it’s a worthy academic exercise though.)

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