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Comment by cubefox | Hacker News Reader

Problem specifically in Haskell is that you have to worry about implementing tail recursion to get efficient stack usage. That's not necessary for loops, which Haskell doesn't support. Though other functional languages do support them.

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Haskell most definitely supports loops:

    ghci> :{
    ghci| for_ [1 .. 10] $ \i ->
    ghci|   print i
    ghci| :}
    1
    2
    3
    4
    5
    6
    7
    8
    9
    10

It doesn't require loops to be implemented at the language level, however. The language is rich enough to support user-defined loop constructs.

Loop constructs like whileM_ require extra IORef effort to the point where people actually recommend recursion (with tail recursion) instead, which is still harder to implement than conventional while loops.

Digging through the current Haskell standard library - for_ calls traverse_, which calls foldr, which calls foldMap, which calls… foldr. Found the recursion! The person you’re replying to is correct - you can mimic the style of a for loop, but under the hood all of this stuff is going to be implemented with recursion (and tail recursion, if you don’t want to hate your life).

I also may have gotten some detail slightly wrong, the code in Data.Foldable is kinda weird and I haven’t Haskell’d in a while

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