Haskell programs side effect all the time, there's no prohibition or even cultural aversion to effects. The only "effect"-related thing we really avoid is the way in many languages one uses the stack, the heap, and static memory as a myriad of little ad hoc in-process databases.
A lot of languages I look at as essentially DSLs for creating multitudes of ad hoc databases. The simplest form of a database is an IORef, which haskell has and haskellers use, but a lot of languages have dedicated syntax for IORefs (e.g. when every variable implicitly is one).
Haskellers approach a task like "map a function over a list" in a way that doesn't require instantiating a database to track the progress, and that would seem like a very convoluted rube goldberg way to solve the problem, but that doesn't come from a general aversion to effects.
Both kinds of list operations are there...
fmap :: (a -> b) -> [a] -> [b]
traverse :: (a -> IO b) -> [a] -> IO [b]
'traverse' isn't a pariah. You use it to do I/O when you want to do I/O.
fmap :: (a -> b) -> [a] -> [b]
traverse :: (a -> IO b) -> [a] -> IO [b]
'traverse' isn't a pariah. You use it to do I/O when you want to do I/O.
The difference from other langs is that Haskell has *some things* that don't involve I/O. In many langs *everything* is I/O, and in haskell *some* things are I/O, and for merely that it gets this "haskellers hate I/O!" reputation.
It's like when a videogame puts one woman in it and the boys are like "this is excessive, they hate men!"
no, you're just already so excessively steeped in I/O that any touch of something that isn't I/O feels radical
Haskell isn't an extreme; it represents moderation.
A function without I/O:
f x = x + 1
A function with I/O:
g x = print x $> x + 1
f produces its input plus one.
g does the same but prints the input first.
if you like your I/O you can keep your I/O
f x = x + 1
A function with I/O:
g x = print x $> x + 1
f produces its input plus one.
g does the same but prints the input first.
if you like your I/O you can keep your I/O
nobody's coming to take away your I/O
