Haskell – Function

Haskell

Preface

You may not know it, but since the first part up until now we’ve been using functions (Function). For example, the * sign is a function to multiply 2 numbers, and we put the 2 numbers to be multiplied on the left and right of the *. However, most functions that do not take integer arguments are called by placing the parameters to the right of the function name.

How to call the function

Usually in imperative languages ​​we call a function by calling its name, followed by a pair of signs (), inside are parameters, separated by commas.

In Haskell, we call the function by naming the function, followed by the parameters, separated by a space mark. For example:

ghci> succ 8
9

The succ function returns the next value of the passed value, such as succ 8 = 9, succ 'a' = 'b', succ 1.1 = 2.1

Passing multiple parameters, we just write the parameters separated by 1 space mark. For example:

ghci> min 9 10
9
ghci> min 3.4 3.2
3.2
ghci> max 101 101
101

Jaw min get the smallest number between 2 numbers, function max get the largest number between 2 numbers.

Function calls always have a higher priority than regular statements, that is, in a statement with many statements, the function calls will be executed first. For example:

ghci> succ 9 + max 5 4 + 1
16
ghci> (succ 9) + (max 5 4) + 1
16

In the above code then succ 9 and max 5 4 will be called first and then add the results of these two functions together and + 1. Both statements are used () and do not use () all have the same priority.

If we want to execute the following commands first then we have to wrap them in parentheses (). For example:

ghci> max 5 3 * 2
10
ghci> max 5 (3 * 2)
6

If a function accepts 2 Parameters then we can write these 2 parameters on the left and right sides of the function name. However, with this call, we must enclose the function’s name in pairs of signs `` Because Haskell does not know what parameters to pass first and which parameters to pass later. For example:

ghci> 5 `max` 3
5
ghci> max 5 3
5

Function definition

To define a function, we first write it like a function call, then add an = sign and start writing statements inside the function. For example:

ghci> doubleMe x = x + x

In the above code we define the function doubleMe, accept 1 parameter named x. This function will x2 this parameter. Then we can use it as usual:

ghci> doubleMe 9
18
ghci> doubleMe 8.3
16.6

We can use the above function within the definition of another function. For example:

ghci> tripleMe x = doubleMe x + x
ghci> tripleMe 3
9

Hope this helps! 

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