10 Jun
2015
10 Jun
'15
2:55 p.m.
On Wed, Jun 10, 2015 at 11:15 AM Marcin Mrotek
That's why, this is not a pure function because every time you call it, it may return a different string.
This is a common source of confusion. A value of type IO a for some a is not an impure function because it is not a function. Its *evaluation* is completely pure and referentially transparent: every time you evaluate `getLine`, you get the same IO String value. The only observable difference is under execution, but *we don't expect execution to be pure*: we only expect evaluation to be pure.