() {Functional Programming}

Closure#

Lexical Scoping#

To understand closure let's first take a look at Lexical scoping using example below:

func testScope() {  
    var test = “In Lexical Scope”;  
    func insideScope() {        
        cmd.println(test);
    }
}

testScope creates local variable test and instance of function insideScope .

insideScope() displays value of test variable,which is declared in its parent function.

Variable test is not declared in insideScope , still it is accessible.. which is referred as Lexical Scope.

Closer to `Closure`#

Closure is a function enclosed within another function having some variable(state). Example:

func outerFunction() {  
    var a = 10; 
    func innerFunction() {      
        cmd.println(“A Inside: “+a);
    }
    return innerFunction;
}
var useClosure = outerFunction();
useClosure(); # A Inside: 10

Call to outerFunction is returning innerFunction (‘closure’ ) which captures the variable a.

Variable a can be accessed only by innerFunction (in read-only mode) outside its Lexical Scope so it can be referred as variable private to innerFunctionHigher-Order Functions

`function are first-class objects!`#

In cafe, functions are first-class objects. Thus, a function can be assigned to a variable, can be passed as an argument & can be returned inside a function.

When a function is declared, internally a Function object is created and is assigned to variable.

func Hello(){
}
# Is internally interpreted as
# var Hello = `Function` Object                                    

Thus, it becomes possible to use functions as any other variables.

func A(fn){
    fn();
}
func B(){
    cmd.print(“I’m B”);
}
func Z(){
    return B;
}
var obj = {
    Foo: A,
};

var b = obj.Foo(Z);
b(); # I’m B

Anonymous Function#

In cafe anonymous function can be implemented using syntax below: Syntax

func ([params]) {   
    # statements
}

Example:

var acc = {  
    init: func(){    
        this.amount = 0;  
    },  
    updateBal: func(amt){    
        this.amount = this.amount+amt;  
    },  
    checkBalance: func(){    
        cmd.println(this.amount);  
    },  
    deposit: func(b){    
        this.updateBal(b);  
    },  
    withdraw: func(b){    
        if(this.amount < b){      
            cmd.println("Insufficient Balance");    
        } else {      
            updateBal(-b);    
        }  
    }
};
acc.init();
acc.checkBalance();
acc.deposit(1000);
acc.withdraw(2000);
acc.checkBalance();

Closure#

Lexical Scoping#

Closer to Closure#

function are first-class objects!#

Anonymous Function#

Closer to `Closure`#

`function are first-class objects!`#