A binding binds a name or even several names with a function definition.

In Haskell, a binding is defined by symbol “=” whereas

1. on the left hand side
   1. the function name and its parameters
   2. or a pattern is given,
2. and on the right had side the definition of the function.

• examples
  • compile, error and warning free, with compiler: GHC 8.10.4, using compiler option -Wall

• function name an parameter (half x), on the left hand side of the equal sign (=)
  • half is the function that can take parameter x
  • half can be evaluated by name with a parameter just right behind the function name (e.g. half 5)
• function definition (x / 2), on the right hand side
  • if half is demanded to be evaluated then the result is delegated to function (/) with parameter x and 2
• example
  • code line:

    half x = x / 2

  • works in:

    main :: IO ()
    main = 
            do
                    print $ half 5
     
    default (Double)
     
    half x = x / 2

  • with compiler warning, which we ignore for didactic reasons
  • executes, with output:

    2.5

(x1, x2, x3) = (42, "Hello", "World")

…works in…

module Main where
 
main :: IO ()
main = 
        do
                print x1
                print x2
                print x3
 
(x1, x2, x3) = (42, "Hello", "World")

Person name number = Person "Lutz" 1243

…works in…

module Main where
 
main :: IO ()
main = 
        do
                print name
                print number
 
data Person = Person { sName :: String, iNumber :: Integer }
 
Person name number = Person "Lutz" 1243

(x1, Person x2 x3, x4) = ("...", Person "Lutz" 1243, '#')

…works in…

module Main where
 
main :: IO ()
main = 
        do
                print x1
                print x2
                print x3
                print x4
 
data Person = Person { sName :: String, iNumber :: Integer }
 
(x1, Person x2 x3, x4) = ("...", Person "Lutz" 1243, '#')