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I found this code snipped on the internet:
digits 0 = [0] digits n = digits' n [] where digits' 0 ds = ds digits' n ds = let (q,r) = quotRem n 10 in digits' q (r:ds) sumOfDigits = sum . digits Can someone quickly explain what the " ' " sign ( digits n = digits' n [] ) after the recursive function call is for? I've seen some other code examples in Haskell (tutorials), but im not understandig this one. A quick explanation is appreciated.
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It is indeed convention to use a "tick" at the end of a function name to denote a slightly modified version of a previously defined function, but this is nothing other than convention - the apostrophe character has no intrinsic meaning in the Haskell language.
Single quotes means single character, double quotes means character array (string). In Haskell, 'c' is a single character ( Char ), and "c" is a list of characters ( [Char] ).
No, it's not possible, because Haskell variables are immutable, therefore, the creators of Haskell must have reasoned there's no point of passing a reference that cannot be changed.
The apostrophe is just part of the name. It is a naming convention (idiom) adopted in Haskell.
The convention in Haskell is that, like in math, the apostrophe on a variable name represents a variable that is somehow related, or similar, to a prior variable.
An example:
let x = 1 x' = x * 2 in x' x' is related to x, and we indicate that with the apostrophe.
You can run this in GHCi, by the way,
Prelude> :{ Prelude| let x = 1 Prelude| x' = x * 2 Prelude| in x' Prelude| :} 2 It's just another character allowed in identifiers. Think of it as another letter.
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