The Ring programming language version 1.5.2 book - Part 31 of 181
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This document summarizes various functional programming concepts in Ring including pure functions, first-class functions, higher-order functions, anonymous and nested functions, and equality of functions. It also covers reflection and meta-programming capabilities in Ring such as using locals(), globals(), functions(), cfunctions(), islocal(), isglobal(), isfunction(), iscfunction(), packages(), and ispackage() to retrieve and check information about variables, functions, and packages at runtime.
![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
275](https://image.slidesharecdn.com/301pdfsamfayedringdoc1-180227021812/85/The-Ring-programming-language-version-1-5-2-book-Part-31-of-181-1-320.jpg)
![Ring Documentation, Release 1.5.2
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 276](https://image.slidesharecdn.com/301pdfsamfayedringdoc1-180227021812/85/The-Ring-programming-language-version-1-5-2-book-Part-31-of-181-2-320.jpg)
![Ring Documentation, Release 1.5.2
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!
Message from the test function!
Message from the test function!
Message from the test function!
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 277](https://image.slidesharecdn.com/301pdfsamfayedringdoc1-180227021812/85/The-Ring-programming-language-version-1-5-2-book-Part-31-of-181-3-320.jpg)
![Ring Documentation, Release 1.5.2
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 278](https://image.slidesharecdn.com/301pdfsamfayedringdoc1-180227021812/85/The-Ring-programming-language-version-1-5-2-book-Part-31-of-181-4-320.jpg)
The Ring programming language version 1.5.2 book - Part 31 of 181
- 1. 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 5 275
- 2. Ring Documentation, Release 1.5.2 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 276
- 3. Ring Documentation, Release 1.5.2 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! Message from the test function! Message from the test function! Message from the test function! 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 277
- 4. Ring Documentation, Release 1.5.2 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 278
- 5. Ring Documentation, Release 1.5.2 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 40.5. Equality of functions 279
- 6. CHAPTER FORTYONE 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. 41.1 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 41.2 globals() Function We can get a list of variables names in the global scope using the globals() function. Syntax: 280
- 7. Ring Documentation, Release 1.5.2 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: message from test() Global Variables: x y z 41.3 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 41.4 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: 41.3. functions() Function 281
- 8. Ring Documentation, Release 1.5.2 aList = cfunctions() See "Count : " + len(aList) + nl for x in aList see x + "()" + nl next Output: Count : 197 len() add() del() get() clock() ... Note: The complete list is removed from the previous output. 41.5 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 41.6 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: 41.5. islocal() Function 282
- 9. Ring Documentation, Release 1.5.2 x=10 y=20 test() func test see isglobal("x") + nl + isglobal("y") + nl + isglobal("z") + nl Output: 1 1 0 41.7 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 41.8 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 41.7. isfunction() Function 283
- 10. Ring Documentation, Release 1.5.2 Output: 1 1 0 41.9 packages() Function We can get a list of packages names using the packages() function. Syntax: packages() --> a list contains packages names Example: See packages() Package Package1 Class class1 Func f1 Package Package2 Class class1 Func f1 Package Package3 Class class1 Func f1 Package Package4 Class class1 Func f1 Output: package1 package2 package3 package4 41.10 ispackage() Function We can check if a package is defined or not using the ispackage() function. Syntax: ispackage(cPackageName) --> returns 1 if the Package is defined returns 0 if the Package is not defined Example: See ispackage("package1") + nl + ispackage("package4") + nl + ispackage("package5") + nl + ispackage("package3") + nl 41.9. packages() Function 284