The Ring programming language version 1.5.3 book - Part 31 of 184

Ring Documentation, Release 1.5.3
Func main
e1 = new Employee {
Name = "test"
age = 20
job = "programmer"
salary = 20000000
print()
}
Class Human
Name Age
func print
see "Name : " + name + nl + "Age : " + age + nl
Class Employee from Human
Job Salary
func print
super.print()
see "Job : " + job + nl + "Salary : " + salary + nl
Output:
Name : test
Age : 20
Job : programmer
Salary : 20000000
39.8 Dynamic Attributes
We can write instructions after the class name to be executed when we create new objects
Example:
o1 = new dynamicClass
see o1.var5 + nl # output 5
Class DynamicClass
for x = 1 to 10
cStr = "var" + x + " = " + x
eval(cStr)
next
Tip: in the previous example var1, var2, ..., var10 will be defined as attributes.
Tip: The problem with the previous example is that x and cStr will be defined as attributes too!
Note: we can write class definitions inside a string then using eval() we can execute the string to define the classes
39.9 Packages
We can create a package (a group of classes under a common name) using the next syntax
39.8. Dynamic Attributes 275

package PackageName
Class Class1
...
Class Class2
...
Class Class3
...
...
Example
o1 = new System.output.console
o1.print("Hello World")
Package System.Output
Class Console
Func Print cText
see cText + nl
Note: we can use the dot operator as part of the package name
Instead of typing the long name PackageName.ClassName we can use the import command
When we import a package, we can use any class inside this package directly.
Example
import system.output
o1 = new console {
print("Hello World")
}
Package System.Output
Class Console
Func Print cText
see cText + nl
39.10 Printing Objects
We can print the object state (attributes and values) using the see command.
Example:
see new point { x=10 y=20 z=30 }
class point x y z
Output:
x: 10.000000
y: 20.000000
z: 30.000000
39.11 Find() and List of Objects
We can use the ﬁnd() function to search inside a list of objects.
Syntax:
39.10. Printing Objects 276

Find(List,ItemValue,nColumn,cAttribute) ---> Item Index
Example:
myList1 = [new Company {position=3 name="Mahmoud" symbol="MHD"},
new Company {position=2 name="Bert" symbol="BRT"},
new Company {position=1 name="Ring" symbol="RNG"}
]
see find(mylist1,"Bert",1,"name") + nl
see find(mylist1,"Ring",1,"name") + nl
see find(mylist1,"Mahmoud",1,"name") + nl
see find(mylist1,"RNG",1,"symbol") + nl
see find(mylist1,"MHD",1,"symbol") + nl
see find(mylist1,"BRT",1,"symbol") + nl
see find(mylist1,3,1,"position") + nl
see find(mylist1,1,1,"position") + nl
see "Other" + nl
see find(mylist1,"test",1,"name") + nl
class company position name symbol
Output:
2
3
1
3
1
2
1
3
Other
0
0
0
39.12 Sort() and list of objects
We can sort a list of objects based on an object attribute using the Sort() function.
Syntax:
Sort(List,nColumn,cAttribute) ---> Sorted List based on Object Attribute
Example:
myList1 = [
new Company {position=3 name="Mahmoud" symbol="MHD"},
new Company {position=2 name="Bert" symbol="BRT"},
new Company {position=8 name="Charlie" symbol="CHR"},
new Company {position=6 name="Easy" symbol="FEAS"},
new Company {position=7 name="Fox" symbol="EFOX"},
new Company {position=5 name="Dog" symbol="GDOG"},
new Company {position=4 name="George" symbol="DGRG"},
39.12. Sort() and list of objects 277

new Company {position=1 name="Ring" symbol="RNG"}
]
see sort(mylist1,1,"name")
see copy("*",70) + nl
see sort(mylist1,1,"symbol")
see copy("*",70) + nl
see sort(mylist1,1,"position")
class company position name symbol
Output:
position: 2.000000
name: Bert
symbol: BRT
position: 8.000000
name: Charlie
symbol: CHR
position: 5.000000
name: Dog
symbol: GDOG
position: 6.000000
name: Easy
symbol: FEAS
position: 7.000000
name: Fox
symbol: EFOX
position: 4.000000
name: George
symbol: DGRG
position: 3.000000
name: Mahmoud
symbol: MHD
position: 1.000000
name: Ring
symbol: RNG
**********************************************************************
position: 2.000000
name: Bert
symbol: BRT
position: 8.000000
name: Charlie
symbol: CHR
position: 4.000000
name: George
symbol: DGRG
position: 7.000000
name: Fox
symbol: EFOX
position: 6.000000
name: Easy
symbol: FEAS
position: 5.000000
name: Dog
symbol: GDOG
position: 3.000000
name: Mahmoud
39.12. Sort() and list of objects 278

symbol: MHD
position: 1.000000
name: Ring
symbol: RNG
**********************************************************************
position: 1.000000
name: Ring
symbol: RNG
position: 2.000000
name: Bert
symbol: BRT
position: 3.000000
name: Mahmoud
symbol: MHD
position: 4.000000
name: George
symbol: DGRG
position: 5.000000
name: Dog
symbol: GDOG
position: 6.000000
name: Easy
symbol: FEAS
position: 7.000000
name: Fox
symbol: EFOX
position: 8.000000
name: Charlie
symbol: CHR
39.13 Using Self.Attribute and Self.Method()
Inside the class region (After the class name and before any method) and the class methods we can use self.attribute
and self.method()
Class Point
self.x = 10
self.y = 20
self.z = 30
func print
see self.x + nl + self.y + nl + self.z + nl
Note: using self.attribute in the class region to define the class attribute protect the class attributes from conflict with
global variables.
Tip: if you typed the class attributes with self.attribute and there are a global variable with the same name it will be
used and the attribute will not be defined.
Check the “Scope Rules” chapter to know about the conflict between the global variable name and the attribute name
Whay this may happens?
Because
• Because in the class region we can access global variables.
39.13. Using Self.Attribute and Self.Method() 279

• Before defining any variable, Ring try to find the variable and use it if it’s found.
Note: Try to avoid the global variables, use the main function and start their names with $
Tip: In large programs protect your classes and define their members using self.attribute
39.14 Using This.Attribute and This.Method()
Inside class methods we have access to the object scope directly. we don’t need to use Self.attribute or Self.method to
read/write attribute and call methods.
But we can use braces {} while we are inside methods to access another object, In this case the current object scope
will be changed while we are inside the brace.
How we can get access to our class attributes and methods while we are inside braces?
This can be done using This.Attribute and This.Method()
Example:
new point
class point
x=10 y=20 z=30
print()
func print
new UI {
display(this.x,this.y,this.z)
}
Class UI
func display x,y,z
see x + nl + y + nl + z + nl
39.14. Using This.Attribute and This.Method() 280

CHAPTER
FORTY
FUNCTIONAL PROGRAMMING
In previous chapters we learned about Functions and Recursion.
In this chapter we are going to learn about more Functional Programming (FP) concepts like
• Pure Functions
• First-class functions
• Higher-order functions
• Anonymous and nested functions.
• Equality of functions
40.1 Pure Functions
We can create pure functions (functions that doesn’t change the state) by the help of the assignment operator to copy
variables (Lists & Objects) by value to create new variables instead of working on the original data that are passed to
the function by reference.
Example:
Func Main
aList = [1,2,3,4,5]
aList2 = square(aList)
see "aList" + nl
see aList
see "aList2" + nl
see aList2
Func Square aPara
a1 = aPara # copy the list
for x in a1
x *= x
next
return a1 # return new list
Output:
aList
1
2
3
4
5
281

aList2
1
4
9
16
25
40.2 First-class Functions
Functions inside the Ring programming language are ﬁrst-class citizens, you can pass functions as parameters, return
them as value or store them in variables.
We can pass/return the function by typing the function name as literal like “FunctionName” or :FunctionName for
example.
We can pass/return functions using the variable that contains the function name.
We can call function from variables contains the function name using the Call command
Syntax:
Call Variable([Parameters])
Example:
Func Main
see "before test2()" + nl
f = Test2(:Test)
see "after test2()" + nl
call f()
Func Test
see "Message from test!" + nl
Func Test2 f1
call f1()
See "Message from test2!" + nl
return f1
Output:
before test2()
Message from test!
Message from test2!
after test2()
Message from test!
40.3 Higher-order Functions
Higher-order functions are the functions that takes other functions as parameters.
Example:
Func Main
times(5,:test)
40.2. First-class Functions 282

Func Test
see "Message from the test function!" + nl
Func Times nCount,F
for x = 1 to nCount
Call F()
next
Output:
Message from the test function!
40.4 Anonymous and Nested Functions
Anonymous Functions are functions without names that can be passed as parameters to other functions or stored in
variables.
Syntax:
Func [Parameters] { [statements] }
Example:
test( func x,y {
see "hello" + nl
see "Sum : " + (x+y) + nl
} )
new great { f1() }
times(3, func { see "hello world" + nl } )
func test x
call x(3,3)
see "wow!" + nl
func times n,x
for t=1 to n
call x()
next
Class great
func f1
f2( func { see "Message from f1" + nl } )
func f2 x
call x()
Output:
hello
Sum : 6
40.4. Anonymous and Nested Functions 283

wow!
Message from f1
hello world
hello world
hello world
Example:
Func Main
aList = [1,2,3,4]
Map (aList , func x {
return x*x
} )
see aList
aList = [4,9,14,25]
Map(aList, :myfilter )
see aList
aList = [11,12,13,14]
Map (aList , func x {
if x%2=0
return "even"
else
return "odd"
ok
})
see aList
Func myfilter x
if x = 9
return "True"
else
return "False"
ok
Func Map aList,cFunc
for x in aList
x = call cFunc(x)
next
Output:
1
4
9
16
False
True
False
False
odd
even
odd
even
40.5 Equality of functions
We can test if function = function or not using the ‘=’ or ‘!=’ operators
40.5. Equality of functions 284

The Ring programming language version 1.5.3 book - Part 31 of 184

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The Ring programming language version 1.5.3 book - Part 31 of 184