Infix operator

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1 Overview

Functions in Haskell are usually called using prefix notation, or the function name followed by its arguments. However, some functions, like +, are called with infix notation, or putting the function name between its two arguments.

2 Using infix functions with prefix notation

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

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

3 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

4 See also

• section of an infix operator
• use of infix operators

Categories: Syntax | Glossary