Difference between revisions of "Infix operator"

From HaskellWiki
Jump to: navigation, search
(Correct a claim: backticks work even for functions with more than two arguments)
m (Various minor changes)
 
Line 2: Line 2:
 
== Overview ==
 
== 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.
+
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 ==
 
== Using infix functions with prefix notation ==
  
Putting parenthesis around an infix operator converts it into a prefix function:
+
Putting parentheses around an infix operator converts it into a prefix function:
  
 
   Prelude> (+) 1 2
 
   Prelude> (+) 1 2
Line 15: Line 18:
 
== Using prefix functions with infix notation ==
 
== Using prefix functions with infix notation ==
  
Putting ` marks around a prefix function allows us to use it like an infix function:
+
Putting <code>`</code>-marks around a prefix function allows us to use it like an infix function:
  
 
   Prelude> let concatPrint x y = putStrLn $ (++) x y
 
   Prelude> let concatPrint x y = putStrLn $ (++) x y

Latest revision as of 23:45, 25 June 2021

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