[icebraining]

I believe the whole fuss of monads is because they allow you to write pure functional programming while still doing I/O and similar things.

http://chris-taylor.github.io/blog/2013/02/09/io-is-not-a-si...

[davidw]

Ok, but if we're being picky about things, you can use all the monads you want, but if you read a file and display its output two different times, you may well get completely different results. The contents could have changed, someone may have removed the file, and so on.

[yvdriess]

Mathematically, you have two different inputs in that case, the environment changed since.