Infix operator

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Overview

Functions in Haskell are usually called using prefix notation, or the function name followed by its arguments. However, some functions e.g. addition are called using infix notation - putting the function name between its two arguments:

 Prelude> 17 + 25
 42

Using infix functions with prefix notation

Putting parentheses around an infix operator converts it into a prefix function:

 Prelude> (+) 1 2
 3
 Prelude> (*) 3 4
 12

Using prefix functions with infix notation

Putting `-marks around a prefix function allows us to use it like an infix function:

 Prelude> let concatPrint x y = putStrLn $ (++) x y
 Prelude> concatPrint "a" "b"
 ab
 Prelude> "a" `concatPrint` "b"
 ab

Note that you can only normally do this with a function that takes two arguments. Actually, for a function taking more than two arguments, you can do it but it's not nearly as nice (note the need for extra parentheses):

Prelude> foldl (+) 0 [1..5]
15
Prelude> ((+) `foldl` 0) [1..5]
15

See also