The Ring programming language version 1.8 book - Part 37 of 202

CHAPTER
FORTYTHREE
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
43.1 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
331

Ring Documentation, Release 1.8
aList2
1
4
9
16
25
43.2 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!
43.3 Higher-order Functions
Higher-order functions are the functions that takes other functions as parameters.
Example:
Func Main
times(5,:test)
43.2. First-class Functions 332

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!
43.4 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
43.4. Anonymous and Nested Functions 333

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
43.5 Equality of functions
We can test if function = function or not using the ‘=’ or ‘!=’ operators
43.5. Equality of functions 334

Example:
f1 = func { see "hello" + nl }
f2 = func { see "how are you?" + nl }
f3 = f1
call f1()
call f2()
call f3()
see (f1 = f2) + nl
see (f2 = f3) + nl
see (f1 = f3) + nl
Output:
hello
how are you?
hello
0
0
1
43.5. Equality of functions 335

CHAPTER
FORTYFOUR
REFLECTION AND META-PROGRAMMING
Since the Ring programming language is a dynamic language, we can get answers about the program code and we can
modify our code during the runtime.
In this chapter we will learn about this and the available functions to use.
• locals()
• globals()
• functions()
• cfunctions()
• islocal()
• isglobal()
• isfunction()
• iscfunction()
• packages()
• ispackage()
• classes()
• isclass()
• packageclasses()
• ispackageclass()
• classname()
• objectid()
• isobject()
• attributes()
• methods()
• isattribute()
• isprivateattribute()
• ismethod()
• isprivatemethod()
• addattribute()
• addmethod()
336

• getattribute()
• setattribute()
• mergemethods()
• packagename()
44.1 locals() Function
We can get a list of variables names in the current scope using the locals() function.
Syntax:
locals() --> a list contains the variables names in the current scope
Example:
test("hello")
func test cMsg
see cMsg + nl
x = 10
y = 20
z = 30
see locals()
Output:
hello
cmsg
x
y
z
44.2 globals() Function
We can get a list of variables names in the global scope using the globals() function.
Syntax:
globals() --> a list contains variables names in the global scope
Example:
x=10 y=20 z=30
test()
func test
see "message from test()" + nl +
"Global Variables:" + nl
see globals()
Output:
44.1. locals() Function 337

message from test()
Global Variables:
x
y
z
44.3 functions() Function
We can get a list of functions names written in the Ring language using the functions() function.
Syntax:
functions() --> a list contains functions names
Example:
see functions()
func f1
see "f1" + nl
func f2
see "f2" + nl
func f3
see "f3" + nl
Output:
f1
f2
f3
44.4 cfunctions() Function
We can get a list of functions names written in the C language using the cfunctions() function.
Syntax:
cfunctions() --> a list contains functions names
Example:
aList = cfunctions()
See "Count : " + len(aList) + nl
for x in aList
see x + "()" + nl
next
Output:
Count : 205
len()
add()
del()
get()
44.3. functions() Function 338

clock()
...
Note: The complete list is removed from the previous output.
44.5 islocal() Function
We can check if a variable is deﬁned in the local scope or not using the islocal() function.
Syntax:
islocal(cVariableName) --> returns 1 if the variable is defined in the local scope
returns 0 if the variable is not defined in the local scope
Example:
test()
func test
x=10 y=20
see islocal("x") + nl +
islocal("y") + nl +
islocal("z") + nl
Output:
1
1
0
44.6 isglobal() Function
We can check if a variable is deﬁned in the global scope or not using the isglobal() function.
Syntax:
isglobal(cVariableName) --> returns 1 if the variable is defined in the global scope
returns 0 if the variable is not defined in the global scope
Example:
x=10 y=20
test()
func test
see isglobal("x") + nl +
isglobal("y") + nl +
isglobal("z") + nl
Output:
1
1
0
44.5. islocal() Function 339

44.7 isfunction() Function
We can check if a Ring function is deﬁned or not using the isfunction() function.
Syntax:
isfunction(cFunctionName) --> returns 1 if the Ring function is defined
returns 0 if the Ring function is not defined
Example:
see isfunction("f1") + nl +
isfunction("f2") + nl +
isfunction("f3") + nl
func f1
see "message from f1()" + nl
func f2
see "message from f2()" + nl
Output:
1
1
0
44.8 iscfunction() Function
We can check if a C function is deﬁned or not using the iscfunction() function.
Syntax:
iscfunction(cFunctionName) --> returns 1 if the C function is defined
returns 0 if the C function is not defined
Example:
see iscfunction("len") + nl +
iscfunction("add") + nl +
iscfunction("test") + nl
Output:
1
1
0
44.9 packages() Function
We can get a list of packages names using the packages() function.
Syntax:
packages() --> a list contains packages names
44.7. isfunction() Function 340

The Ring programming language version 1.8 book - Part 37 of 202

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The Ring programming language version 1.8 book - Part 37 of 202