The Ring programming language version 1.9 book - Part 39 of 210

Ring Documentation, Release 1.9
The “len” operator is used with (for in) control structure.
The “[]” operator is used when we try to access the list items, In this case we use the & operator to return the item
values like strings an numbers by reference, so we can update it when we access the items.
Another Example
func main
See "----1"+nl
a1 = new BigNumber( "123" )
See nl+"----2"+nl
a1.print()
a2.print()
a3.print()
See nl+"----3"+nl
a2 = a1 + "45"
See nl+"----4"+nl
a2.print()
See nl+"----5"+nl
a3 = a1 + a2
See nl+"----6"+nl
a3.print()
See nl+"----7"+nl
###==================================
Func FuncAdd( num1, num2)
Sum = 0 + num1 + num2 ### Para.aData isNumber
Sum = "" +Sum ### Para.adata isString
return Sum ### return to Class
###===================================
class BigNumber
### Variables
aData = "468"
### Functions INIT default values
func init aPara
? "INIT aPara: " ? aPara
if isString(aPara)
aData = aPara
else
aData = "" + aPara
ok
### Other Functions
func operator cOperator, Para
whatType = Type(Para)
? nl+"WhatType-PARA: "+ whatType ? Para
? nl+"Operator: " ? cOperator ? nl+"PARA: " ? Para ? " ______" ? nl
if whatType = "STRING"
dataInfo = Para
? "dataInfo String: " ? dataInfo
but whatType = "NUMBER"
datinfo = "" + Para
? "dataInfo Number: " ? dataInfo
44.6. Operator Overloading 349

else whatType = "OBJECT"
dataInfo = "" + para.aData
? "dataInfo OBJECT: " ? dataInfo
ok
? "dataInfo USING: " ? dataInfo
### Para.aData does NOT exist on first pass ( Object with member)
### Result isObject when assigned "self"
result = self
switch cOperator
on "+"
answer = FuncAdd( aData, dataInfo )
? nl+"AnswerString - FunAdd aData, dataInfo: " ? answer
### result = self, is Object, populate Object with aData member
result.aData = answer
off
### Result = Self is Object
return result
func print
? nl+"ClassPrint aData: " ? aData
44.7 Inheritance
We can create class from another class in the class deﬁnition using the keyword from.
Syntax:
Class <Class Name> [From <Parent Class Name>]
We can call a method in the parent class from the child class using the super object.
Syntax:
func methodname
...
super.methodname()
...
Example:
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
44.7. Inheritance 350

super.print()
see "Job : " + job + nl + "Salary : " + salary + nl
Output:
Name : test
Age : 20
Job : programmer
Salary : 20000000
44.8 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
44.9 Packages
We can create a package (a group of classes under a common name) using the next syntax
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
44.8. Dynamic Attributes 351

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
44.10 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
44.11 Find() and List of Objects
We can use the ﬁnd() function to search inside a list of objects.
Syntax:
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
44.10. Printing Objects 352

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
44.12 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"},
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
44.12. Sort() and List of Objects 353

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
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
44.12. Sort() and List of Objects 354

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
44.13 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.
• 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
44.14 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.
44.13. Using Self.Attribute and Self.Method() 355

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
44.15 Using This in the class region as Self
The class region is the region that comes after the class name and before any method.
We can use This in the class region as Self.
Example:
func main
o1 = new program {
test()
}
? o1
class program
this.name = "My Application"
this.version = "1.0"
? name ? version
func test
? "Name = " + name
? "Version = " + version
Output
My Application
1.0
Name = My Application
Version = 1.0
name: My Application
version: 1.0
Note: When we use braces to change the current active object, Using This we can still point to the class.
44.15. Using This in the class region as Self 356

Tip: The difference between This and Self is that Self point to the current active object that we can change using
braces.
Remember that in most cases we don’t need to use This or Self in the class region
We can write
class program name version
Or
class program name="My Application" version="1.0"
Note: We use This or Self in the class region just to avoid conﬂict with global variables that are deﬁned with the same
name.
44.16 Default value for object attributes
The default value for object attributes is NULL
In Ring, the NULL value is just an empty string or a string that contains “NULL”
We can check for NULL values using the isNULL() function
Example:
oProgram = new Program
? oProgram.name
? oProgram.version
? isNULL(oProgram.name)
? isNULL(oProgram.version)
oProgram { name="My Application" version="1.0" }
? isNULL(oProgram.name)
? isNULL(oProgram.version)
? oProgram
class program
name
version
Output:
NULL
NULL
1
1
0
0
name: My Application
version: 1.0
44.16. Default value for object attributes 357

CHAPTER
FORTYFIVE
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
45.1 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
358

The Ring programming language version 1.9 book - Part 39 of 210

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The Ring programming language version 1.9 book - Part 39 of 210