CODEWITHSUNDEEP
haskelloperator-precedence
t0ma5
t0ma5

Reputation: 155

rules of operator's $ usage in haskell

I tried the $ operator and came to a weird point where I don't understand what is happening. 

f = double $ 3+4

but this does not 

f xs = xs !! $ length xs - 1

Can the operator $ only appear after function names and not after operators? If so is there a way to write the following function without the parenthesis

f xs = xs !! (length xs - 1)

Upvotes: 1

Views: 114

Answers (2)

randomusername
randomusername

Reputation: 8105

Haskell infix notation is problematic, avoid it like this

f xs = (!!) xs $ length xs - 1

The brackets turn an infix operator into a prefix function.

Upvotes: 0

bheklilr
bheklilr

Reputation: 54068

You can't have two operators next to each other, it's invalid syntax. This holds true for all operators. So xs !! $ length xs - 1 just will not work. There isn't really a good way to get rid of the parens in that statement without resorting to some tricks that aren't worth it and make the code less readable.

The $ operator does not have to appear after function names, though, you can do

> let add x y = x + y
> add 1 $ add 2 $ add 3 4

Upvotes: 2

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